SCHOOL OF MECHANICAL
DEPARTMENT OF MECHANICAL ENGINEERING
LESSON NOTES
U4MEA15 MANUFACTURING TECHNOLOGY-II
VELTECH Dr.RR & Dr.SR TECHNICAL UNIVERSITY
1
U4MEA15
MANUFACTURING TECHNOLOGY – II
LTPC
3003
OBJECTIVE:
To Understand The Concept And Basic Mechanics Of Metal Cutting, Working Of Standard
Machine Tools Such As Lathe, Shaping And Allied Machines, Milling, Drilling And Allied
Machines, Grinding And Allied Machines And Broaching. To Understand The Basic
Concepts Of (CNC) Computer Numerical Control Of Machine Tools And CNC
Programming.
UNIT I: THEORY OF METAL CUTTING
9
Introduction: Material Removal Processes, Types Of Machine Tools – Theory Of Metal
Cutting: Chip Formation, Orthogonal Cutting, Cutting Tool Materials, Tool Wear, Tool Life,
Surface Finish, Cutting Fluids.
UNIT II: CENTRE LATHE AND SPECIAL PURPOSE LATHES
9
Centre Lathe, Constructional Features, Cutting Tool Geometry, Various Operations, Taper
Turning Methods, Thread Cutting Methods, Special Attachments, Machining Time And
Power Estimation. Capstan And Turret Lathes – Automats – Single Spindle, Swiss Type,
Automatic Screw Type, Multi Spindle - Turret Indexing Mechanism, Bar Feed Mechanism.
UNIT III: MACHINE TOOLS
9
Shaper, Planer, Slotter, Milling- Types And Operations. Drilling – Types And Operations Broaching Machines-Push, Pull Broaching Machines. Gear Cutting, Forming, Generation
And Gear Finishing Process.
Abrasive Processes: Grinding Wheel – Specifications And Selection, Types Of Grinding
Process – Cylindrical Grinding, Surface Grinding, Centreless Grinding– Honing, Lapping,
Super Finishing, Polishing And Buffing
UNIT IV: UNCONVENTIONAL MACHINING PROCESS
9
Unconventional Machining Process - Classification, Abrasive Jet Machining, Ultrasonic
Machining, Electric Discharge Machining, Electron Beam Machining, Laser Beam
Machining, Ion Beam Machining, Electro Chemical Machining.
UNIT V: CNC MACHINE TOOLS AND PART PROGRAMMING
9
Numerical Control (NC) Machine Tools – CNC: Types, Constructional Details, Special
Features – Design Considerations Of CNC Machines For Improving Machining Accuracy –
Structural Members – Slide Ways –Linear Bearings – Ball Screws – Spindle Drives And
Feed Drives. Part Programming Fundamentals – Manual Programming – Computer Assisted
Part Programming.
TOTAL : 45 Periods
2
TEXT BOOKS
1. Sharma, P.C., A Textbook Of Production Technology - Vol I And II, S. Chand & Company
Ltd., New Delhi, 1996
2. Rao, P.N., Manufacturing Technology, Vol I & II, Tata Mcgraw Hill Publishing Co., New
Delhi, 1998
REFERENCE BOOKS
1. HMT – “Production Technology”, Tata Mcgraw-Hill, 1998.
2. P.N.Rao, ‘CAD/CAM Principles And Applications’, TATA Mc Craw Hill, 2007
3. P.C. Sharma, “A Text Book Of Production Engineering”, S. Chand And Co. Ltd, IV
Edition, 1993.
4. Shrawat N.S. And Narang J.S, ‘CNC Machines’, Dhanpat Rai & Co., 2002.
5. M.P.Groover And Zimers Jr., ‘CAD/CAM’ Prentice Hall Of India Ltd., 2004.
6. Milton C.Shaw, ‘Metal Cutting Principles’, Oxford University Press, Second Edition,
2005.
7. Philip F.Ostwald And Jairo Munoz, ‘Manufacturing Processes And Systems’, John Wiley
And Sons, 9th Edition,2002.
3
UNIT – I
THEORY OF METAL CUTTING
PART – A
Process Of Metal Shaping.
Process Of Metal Shaping Is Classified Into Two Types Namely.
i.
Non-Cutting Shaping Process
ii.
Cutting Shaping Process
Non-Cutting Shaping Process.
The Metal Is Shaped Under The Action Of Force, Heating Or Both. Since
There Is No Cutting Of Metal, Chip Formation Will Not Be There. So, It Is Called
Non-Cutting Shaping Process.
Cutting Shaping Process.
The Required Shape Of Metal Is Obtained By Removing The Unwanted
Material From The Work Piece In The Form Of Chips Is Called Cutting Shaping
Process. Example: Turning, Drilling, Milling, Boring Etc.
Relative Motion Between Work Piece And Cutting Tool.
i.
ii.
iii.
iv.
Rotation Of Work Against The Tool. Example: Turning
Rotation Of Tool Against Work Piece. Example: Drilling, Milling.
Linear Movement Of The Work Piece Against The Tool Example: Planer.
Linear Movement Of The Tool Against The Work. Example – Shaper
The Different Types Of Cutting Tool
a. Single Point Cutting Tool.
b. Multiple Point Cutting Tool.
4
The Various Parts Single Point Cutting Tool.
1. Shank
4. Base
2. Face
5. Nose
3. Flank
6. Cutting Edge
The Various Angles In Cutting Tool.
1. Back Rake Angle
3. End Relief Angle
5. Side Cutting Angle
2. Side Rake Angle
4. Side Relief Angle
6. End Cutting Angle.
Tool Signature
The Various Angles Of Tools Are Mentioned In A Numerical Number In
Particular Order. That Order Is Known As Tool Signature.
The Effect Of Back Rake Angle And Mention The Types
Back Rake Angle Of Tool Increases The Strength Of Cutting Tool And Cutting
Action.
It Is Classified Into Two Types:
1. Positive Rake Angle
2. Negative Rake Angle
Side Rake Angle And Mention Its Effects
The Angle Between The Tool Face And The Line Parallel To The Base Of The
Tool Is Known As Side Rake Angle. It Is Used To Control Chip Flow.
Clearance Angle And Mention The Types
These Are The Slopes Ground Downwards From The Cutting Edges. The
Clearance Angle Can Be Classified Into Two Types.
i.
Side Relief Angle.
5
ii.
End Relief Angle.
The Nose Radius.
It Is The Joining Of Side And End Cutting Edges By Means Of Small Radius
In Order To Increase The Tool Life And Better Surface Finish On The Work Piece.
All Conditions For Using Positive Rake Angle
a.
b.
c.
d.
e.
To Machine The Work Hardened Materials.
To Machine Low Strength Ferrous And Non-Ferrous Metals.
To Turn The Long Shaft Of Small Diameters.
To Machine The Metal Below Recommended Cutting Speeds.
To Machine The Workpiece Using Small Machine Tools With Low
Horsepower.
The Negative Rake Angles
a. To Machine High Strength Alloys.
b. The Machine Tools Are More Rigid.
c. The Feed Rates Are High.
d. To Give Heavy And Interrupted Cuts.
Types Of Metal Cutting Process.
The Metal Cutting Processes Are Mainly Classified Into Two Types.
a. Orthogonal Cutting Process(Two Dimensional Cutting)
b. Oblique Cutting Process (Three Dimensional Cutting)
Orthogonal And Oblique Cutting.
Orthogonal Cutting: The Cutting Edge Of Tool Is Perpendicular To The Workpiece
Axis.
Oblique Cutting: The Cutting Edge Is Inclined At An Acute Angle With Normal To
The Cutting Velocity Vector Is Called Oblique Cutting Process.
6
Shear Plane
The Material Of Work Piece Is Stressed Beyond Its Yield Point Under The
Compressive Force. This Causes The Material To Deform Plastically And Shear Off.
The Plastic Flow Takes Place In A Localized Region Called Shear Plane.
Cutting Force
The Sheared Material Begins To Flow Along The Cutting Tool Face In The
Form Of Small Pieces. The Compressive Force Applied To Form The Chip Is Called
Cutting Force.
Chip And Its Different Types
The Sheared Material Begins To Flow Along The Cutting Tool Face In The Form Of
Small Pieces Is Called Chip. Chips Are Mainly Classified Into Three Types:
a. Continuous Chip
b. Discontinuous Chip
c. Continuous Chip With Built Up Edge.
Continuous Chip Formed
The Following Factors Favour The Formation Of Continuous Chip.
I. Ductile Material
Ii. Smaller Depth Of Cut
Iii. High Cutting Speed
Iv. Large Rake Angle
V. Sharp Cutting Edge
Vi. Proper Cutting Fluid
Vii. Low Friction Between Tool Face And Chips.
The Favourable Factors For Discontinuous Chip Formation
a.
b.
c.
d.
e.
f.
Machining Of Brittle Material
Small Rake Angle
Higher Depth Of Cut
Low Cutting Speeds
Excess Cutting Fluid
Cutting Ductile Material With Low Speed And Small Rake Angle Of The Tool
7
The Favourable Factors For Continuous Chip With Built Up Edge
a.
b.
c.
d.
e.
f.
Low Cutting Speed
Small Rake Angle
Coarse Feed
Strong Adhesion Between Chip And Tool Face.
Insufficient Cutting Fluid
Large Uncut Thickness
Chip Thickness Ratio
The Ratio Of Chip Thickness Before Cutting To Chip Thickness After Cutting
Is Called Chip Thickness Ratio.
t
l
Chip thickness ratio, r = 1  2
t 2 l1
Chip Reduction Co-Efficient
The Reciprocal Of Chip Thickness Ratio Is Called Chip Reduction CoEfficient.
1
k
r
The Purposes Of Chip Breakers
The Chip Breakers Are Used To Break The Chips Into Small Pieces For
Removal, Safety And To Prevent Both The Machine And Work Damage.
The Difficulties Involved Due To Long And Continuous Chip
During Machining, Long And Continuous Chip That Are Formed At High
Cutting Speed Will Affect Machining. It Will Spoil Tool, Work And Machine. These
Chips Are Hard, Sharp And Hot. It Will Be Difficult To Remove Metal And Also
Dangerous To Safety.
8
The Different Types Of Chip Breakers.
The Chip Breakers Are Classified Into Three Types.
a. Step Type
b. Groove Type
c. Clamp Type
Cutting Forces Acting On The Cutting Tool
During The Cutting Process, The Following Three Components Of Cutting Forces
Are Acting Mutually Right Angles.
a. Feed Force Fx Acts In A Horizontal Plane But In The Direction Opposite To
Feed.
b. Thrust Force Fy Acts In A Direction Perpendicular To The Generated Surface.
c. Cutting Force Fz Acts In The Direction Of The Main Cutting Motion.
The Assumption Made In Merchant Circle
a. The Chip Formation Will Be Continuous Without Built Up Edge.
b. During Cutting Process, Cutting Velocity Remains Constant.
c. The Cutting Tool Has A Sharp Cutting Edge So That It Does Not Make Flank
Contact To The Work Piece.
Metal Removal Rate
It Is Defined As The Volume Of Metal Removed In Unit Time. It Is Used To
Calculate Time Required To Remove Specified Quantity Of Material From The Work
Piece.
The Assumptions Made In Lee And Shaffer’s Theory
a. The Work Ahead Of The Tool Behaves As Ideal Plastic Mass.
b. There Exists A Shear Plane Which Separates The Chip And Work Piece.
9
c. No Hardening In Chip Occurs.
The Tool Energy Of The Cutting Process.
Total Energy Per Unit Volume Is Approximate Equal To The Sum Of Following Four
Energies.
a. Shear Energy Per Unit Volume In Shear Plane.
b. Friction Energy Per Unit Volume In Tool Face.
c. Surface Energy Per Unit Volume Due To The Formation Of A New Surface
Area Is Cutting.
d. Momentum Energy Per Unit Volume Due To The Change In Momentum
Associated With The Metal As It Crosses The Shear Plane.
Machinability Of Metal.
Machinability Is Defined As The Ease With Which A Material Can Be
Satisfactorily Machined.
The Factors Affecting The Machinability
a.
b.
c.
d.
e.
Chemical Composition Of Work Piece Material.
Microstructure Of Work Piece Material
Mechanical Properties Like Ductility, Toughness Etc.
Physical Properties Of Work Materials.
Method Of Production Of The Work Materials.
The Tool Variables Affecting The Machinability
a. Tool Geometry And Tool Material
b. Nature Of Engagement Of Toll With The Work
c. Rigidity Of Tool
The Machine Variables Affecting The Machinability
a. Rigidity Of Machine
b. Power And Accuracy Of The Machine Tool
10
Machinability Evaluated
The Following Criteria Are Suggested For Evaluating Machinability:
a.
b.
c.
d.
e.
f.
g.
h.
Tool Life Per Grind
Rate Of Removal Per Tool Grind
Magnitude Of Cutting Forces And Power Consumption
Surface Finish
Dimensional Stability Of Finished Work
Heat Generated During Cutting
Ease Of Chip Disposal
Chip Hardness, Shape And Size
Advantage Of High Machinability.
a.
b.
c.
d.
e.
Good Surface Finish Can Be Produced.
High Cutting Speed Can Be Used
Less Power Consumption
Metal Removal Rate Is High
Less Tool Wear.
Machinability Index
It Is A Composition Of Machinability Of Different Material To Standard
Materials. US Material Standard For 100% Machinability Is SAE 1112 Hot Rolled
Steel.
Machinability index, I =
Cutting speed of material investigated for 20 minutes tool life
Cutting speed of s tan dard steel for 20 minutes tool life
The Tool Wear.
The Tool Wear Is Generally Classified As Follows.
i. Flank Wear Or Crater Wear
Ii. Face Wear
iii.
Nose Wear
11
Tool Life Is Defined
Tool Life Is Defined As The Time Elapsed Between Two Consecutive Tool
Resharpening. During This Period The Tool Serves Effectively And Efficiently.
Taylor’s Tool Life Equation.
Taylor’s Tool Life Equation
Vtn = C
Where.
V = Cutting Speed In M/Min
T = Tool Life In Minute
C = Constant
N = Index Depends Upon Tool And Work
The Ways Of Representing Tool Life
The Following Are Some Of The Ways Of Expressing Tool Life.
1. Volume Of Metal Removed O Expressing Tool Life.
2. Number Of Work Piece Machined Per Grind
3. Time Unit
The Factors Affecting Tool Life
I. Cutting Speed
Ii. Feed And Depth Of Cut
Iii. Tool Geometry
Iv. Tool Material
V. Cutting Fluid
Vi. Work Material
Vii. Rigidity Of Work, Tool And Machine
The Factors Considered For The Selection Of Cutting Speed
1.
2.
3.
4.
5.
6.
Tool Life
Properties Of Material Being Machined
Rate Of Feed
Depth Of Cut
Tool Geometry
Cutting Fluid Used
12
7. Type Of Machining Process
8. Surface Finish To Be Obtained
The Factors To Be Considered For The Selection Of Tool Materials
i.
ii.
iii.
iv.
v.
Volume Of Production
Tool Design
Type Of Machining Process
Physical And Chemical Properties
Rigidity And Condition Of Machine
The Important Properties Of Cutting Tool Materials
i.
ii.
iii.
iv.
v.
vi.
Hot Hardness
Wear Resistance
High Thermal Conductivity
Resistance To Thermal Shock
Easy To Grind And Sharpen
Low Mechanical And Chemical Affinity For The Work Material.
Four Tools Material.
i.
ii.
iii.
iv.
v.
Carbon Tool Steel
High Speed Steel
Cemented Carbides
Ceramics
Diamonds
The Function Of Cutting Fluids
i.
ii.
iii.
iv.
v.
vi.
It Is Used To Cool The Cutting Tool And Work Piece
It Lubricates The Cutting Tool And Thus Reduces The Co-Efficient Of Friction
Between Tool And Work.
It Improves The Surface Finish As Stated Earlier.
It Causes The Chips To Break Up Into Small Parts.
It Protects The Finished Surface From Corrosion
It Washes Away The Chips From The Tool. It Prevents The Tool From Fouling.
13
vii.
It Prevents Corrosion Of Work And Machine.
The Properties Of Cutting Fluid
i.
ii.
iii.
iv.
v.
vi.
vii.
It Should Have Good Lubricant Properties
High Heat Absorbing Capacity
It Should Have A High Specific Heat, High Heat Conductivity And High Film
Co-Efficient.
High Flash Point
It Should Be Odorless
It Should Be Non-Corrosive To Work And Tool.
It Should Have Low Viscosity To Permit Free Flow Of The Liquid.
Built Up Edge
During Cutting Process, The Interface Temperature And Pressure Are Quite
High And Also High Friction Between Tool Chip Interface Causes The Chip Material
To Weld Itself To The Tool Face Near The Nose. This Is Called Built Up Edge.
The Various Cutting Fluids.
The Cutting Fluids Are Mainly Classified Into Two Types Namely
I. Water Based Cutting Fluids
Ii. Straight Or Heat Oil Based Cutting Fluids.
Differentiate Between Orthogonal Cutting And Oblique Cutting.
S. No
1
2
3
4
Orthogonal Cutting
The Cutting Edge Of The Tool Is
Perpendicular To The Cutting
Velocity Vector
The Chip Flows Over The Tool Face
And The Direction Of Chip-Flow
Velocity Is Normal To The Cutting
Edge
The Cutting Edge Clears The Width
Of The Work Piece On Either Ends
(I.E.No Side Flows
The Maximum Chip Thickness
14
Oblique Cutting
The Cutting Edge Is Inclined At An Acute
Angle With The Normal To The Cutting
Velocity Vector
The Chip Flows On The Tool Face Making
An Angle With The Normal On The Cutting
Edge
The Cutting Edge May Or May Not Clear
The Width Of The Work Piece.
The Maximum Chip Thickness May Not
Occurs At Its Middle
Occur At The Middle
Relief/Clearance Angles Never Be Zero Or Negative
It Relief/ Clearance Angles Are Zero Or Negative The Tool Will Rub Against
The Job. So, Tool Will Get Overhead And Cutting Is Not Proper. So, You Will Get A
Poor Surface Finish.
Negative Rake Angle
The Slope Given Away From The Cutting Edge Is Called Negative Rake
Angle.
The Diamond Tools Be Used
Diamond Is The Hardest Material. It Is Used For Machining Very Hard
Materials Such As Glass, Plastics, Ceramics Etc.
The Advantages Of Increasing Nose Radius
If The Nose Radius Increases The Strength Of Cutting Tool Is Increased And
It Is Used On Castings And Cast Iron, Where The Cuts Are Interrupted.
The Equations Of Velocity Of Chip And Velocity Of Shear In Terms Of Cutting
Velocity, Rake Angle And Shear Angle.
Velocity of chip, Vc 
V Sin
Cos     
Velocity of shear, Vs 
V Cos
Cos   - 
The Shear Angle In Terms Of Chip Thickness And Rake Angle Of The Tool.
 r Cos 
Shear angle,  =tan -1 
1-rSin 
15
The Composition Of High-Speed Steel
High-Speed Steel Contains Tungsten – 18% And Vanadium – 1%. It Has
About 0.75% Carbon.
The Causes Of Wear
The Tool Is Subjected To Three Important Factors Such As Force, Temperature
And Sliding Action Due To Relative Motion Between Tool And The Work Piece. So,
The Tool Is Wear Easily.
16
PROBLEMS:
1. A Mild Steel Work Piece Of 60mm Diameter Is To Be Turned With An
Orthogonal Tool To A Feed Rate Of 0.92 Mm/Revolution And At 75 Rpm. If The
Chip Thickness Is 2mm, Determine The Chip Thickness Ratio And Length Of
Chip Removed In One Minute. Assume A Condition Of Continuous Chip.
Given Data:
D = 60mm
T1 = 0.92mm
T2 = 2mm
N = 75rpm
To Find:
i.
Chip Thickness Ratio R
ii.
Length Of Chip Removed Per Minute
Solution:
Chip Thickness Ratio,
t 0.92
r 1 
 0.46mm Ans.
t2
2
Length of chip before cutting, l1   DN
=   60  75  14137.16mm
l
We know that, chip thickness ratio = r = 2
l1
0.46 =
l2
 l2  6503mm Ans.
14137.16
Result:
1. Chip thickness ratio, r = 0.46
2. Length of chip removed per minute, l2  6503mm
2. During An Orthogonal Cutting A Chip Length Of 160mm Was Obtained From
An Uncut Length Of 350mm. The Cutting Tool Has 220 Rake Angle And A Depth
Of Cut Is 0.8mm. Determine The Shear Plane Angle And Chip Thickness
17
Given Data:
l2  160mm
l1  350mm
  22o
t1  0.8mm
To find:
1. Shear plane angle   
2.Chipthickness  t2 
Solution:
Chip thickness ratio, r =
l2 160

 0.457
l1 350
 r cos  
Shear plane angle  = tan -1 
1  r sin  
 0.457  cos 22 
= tan -1 
1  0.457  sin 22 
  270
Ans.
We know that, chip thickness
t
r= 1
t2
0.457=
0.8
t2
t2  1.75mm
Ans.
Result:
1. Shear plane angle, =27 o
2.Chipthicknes, t2  1.75mm
3. In Orthogonal Cutting Process The Following Observations Were Made
Depth Of Cut = 0.25mm
Chip Thickness Ratio = 0.45
Width Of Cut = 4mm
Cutting Velocity = 40m/Min
18
Cutting Force Component Parallel To Cutting Velocity Vector = 1150N
Cutting Force Component Normal To Cutting Velocity Vector = 140N
Rake Angle = 180
Determine Resultant Cutting Force, Power Of Cutting, Shear Plane Angle, Friction
Angle And Force Component Parallel To Shear Plane
Given Data:
t1  0.25mm
r  0.45mm
b  4mm
V  40m / min
Fz  1150 N
Fx  140 N
  18o
To find:
F, power of cutting,  , , and Fs
Solution:
Re sulting cutting forces, F = Fz2  Fx2  1150 2  140 2
F = 1158.49N
Ans.
Power of cutting forces, P = Fx  V  1150  40
= 46000Nm/min
Ans.
 r cos  
Shear angle,   tan  
1  r sin  
 0.45  cos18 
  tan 1 
1  0.45  sin18 
  
Ans.
19
 F  Fz tan  
Friction angle, = tan -1  x

 Fz  Fx tan  
140  1150 tan18 
 = tan -1 
1150  140 tan18 
 = 25o
Ans
Shear force, Fs  Fz cos   Fx sin 
= 1150cos26.5o  140sin 26.5o
Fs  966.7 N
Ans.
Result:
1.Re sul tan t cutting force = 11584.9N
2. Power of cutting force = 46000Nm/min
3. Shear plane angle, =26.5o
4.Friction Angle,   25o
5.Shearforce, Fs  966.7 N
4. A Seamless Tube 32mm Outside Diameter Is Turned On A Lathe. Cutting
Velocity Of The Tool Relative To The Work Piece Is 10m/Min. Rake Angle = 350,
Depth Of Cut = 0.125m, Length Of Chip = 60mm, Horizontal Cutting Force Of The
Tool On The Work Piece = 200N. Cutting Force Required To Hold The Tool
Against The Work Piece = 80N. Calculate
i.
Co-Efficient Of Friction
ii.
Chip Thickness Ratio
iii.
Shear Plane Angle
iv.
Velocity Relative To The Tool, And
v.
Velocity Of Chip Relative To The Work Piece
Given Data:
D = 32mm
V = 10m/Min
 = 350
T1 = 0.125mm
L2 = 60mm
Fz = 200N
Fx = 80N
To Find:
, , R, Vc, And Vs
Solution:
20
 F  Fz tan  
1. Co-efficient of friction,  =  x

 Fz  Fx tan  
 80+200tan35 
= 
 200  80 tan 35 
 = 1.528
Ans.
2.Chip thickness ratio, r =
l2
60
60


l1   D   32
r = 0.5969
Ans.
 r cos  
3. Shear plane angle,  = tan -1 
1  r sin  
 0.5968cos 35 
 = tan -1 
 36.6 o

1

0.5968sin
35


4.Velocity of chip relative to the tool,
Vc  V .r  10  0.5968  5.968m / min
5. Velocity of chip relative to the work piece,
V cos 
10  cos 35
Vs 

cos      cos  36.6  35 
Vs  8.19m / min
Ans
Result:
1.Co  efficient of friction,  =1.528
2. Chip thickness ratio, r = 0.5968
3. Shear plane angle,  =36.60
4.Velocity of chip relative to the tool, Vc  5.968m / min
5.Velocity of chip relative to the work
piece,Vs  8,19m / min
5. The Following Data From The Orthogonal Cutting Test Is Available
Rake Angle = 100
21
Chip Thickness Ratio = 0.35
Uncut Chip Thickness = 0.51mm
Width Of Cut = 3mm
Yield Shear Stress Of Work Material = 285N/Mm2
Mean Friction Coefficient On Tool Face = 0.65
Determine The (I) Cutting Force (Ii) Radial Force
(Iii) Normal Force On The Tool And (Iv) Shear Force On The Tool. [IES–2000]
Given Data:
 = 10o
r  0.35
t1  0.51mm
b  3mm
 = 285N/mm 2
 = 0.65
To Find:
Fz, Fx, N And Fs
Solution:
 r cos  
Shear angle,  =tan -1 
1  r sin  
 0.35cos10 
= tan -1 
1  0.35sin10 
 = 200
 = tan
Friction angle,  = tan -1  tan 1  0.65  33
To find shear stress,  
Fs 
Fs
Sin
A1
  A1 285  0.51 3

sin 
sin 20

Fs  1274.92 N
A1  3  0.51
Ans.
22
Fs  F cos   F cos       
F
Fs
1274.92

cos        cos  20  33  10 
F  1743.23 N
Cutting force, Fs  F cos.     
 1743.23cos 33  10 
Fz  1604.6 N
Ans
F  Fz2  Fx2
 Radial force, Fx  F 2  Fz2  1743.232  1604.62
Fx  681.1N
Ans.
Normal force on the tool,
N = Fz cos   Fx sin 
= 1604.6  cos10-681.1 sin10
N=1461.9N
Ans.
Re sult :
1. Shear force, Fs  1274.92 N
2. Cutting force, Fz  1604.6 N
3. Radial force, Fx  681.1N
4. Normal force on the tool,N = 1461.9N
6. The Following Observations Are Made From A Metal Cutting Test
Cutting Force
=
180kg
Feed
=
5 Cuts/Min
Depth Of Cut
=
5mm
Cutting Speed
=
30mm/Min
If Overall Efficiency Of Machine Is 70% Determine
i.
Normal Pressure On Chip
ii.
Power Required At Motor.
Given Data:
Fz  180kg
t1  5mm
V  30mm / min and  = 70%
To Find:
23
i.
ii.
Normal Pressure On Chip
Power Required
Solution:
Fz
Area of chip
Area of chip = Depth of cut  feed/rev
1
= 5   1mm 2
5
180
Normal pressure =
 180kg / mm 2 Ans.
1
F  V 180  30
ii.Power required, P = z

 1.2 H .P
4500
4500
When efficiency of machine is 70% power required
1.2
at motor =
 1.7 H .P
Ans.
0.7
Result:
i. Normal pressure on chip =
i. Normal pressure on chip = 180kg/mm 2
ii.Power required at motor = 1.7H.P
7. In An Orthogonal Cutting Experiment With A Tool Of Rake Angle  = 70, The
Chip Thickness Was Found To Be 2.5mm When The Uncut Chip Thickness Was
Set To 1mm.
i.
Find The Shear Angle, 
ii.
Find The Friction Angle  Assuming That Merchant’s Formula Holds
Good.
Given Data:
  70
t2  2.5
t1  1mm
To find:
 and 
Solution:
 r cos  
i.Shear angle,   tan 1 

 1  r sin  
24
Where, r - Chip thickness ration =
t1
t2
1
 0.4
2.5
 0.4 cos 7 
= tan -1 
1  0.4sin 7 
=
=  =22.60
Ans.
ii. As per Merchant's theory, 2 +   
2  22.6+ -7=90

2
0
Friction angle,   
Result:
Ans.
i. Shear angle  = 22.6o
ii.Friction angle, = 51.69o
8. If The Relationship For H.S.S Tools Is VT1/8 = C1 And For Tungsten Carbide
Tools Is VT1/5 = C2 And Assuming That At A Speed Of 25m/Min, The Tool Life
Was 3 Hours In
Each Case, Compare Their Cutting Lives At 32m/Min.
Given Data:
VT 1/ 8  C1
...... 1
VT 1/ 5  C2
......  2 
V  25m / min
T  3hrs  180 min
V '  32m / min
To Find:
Compare Cutting Lives At 32m/Min
Solution:
From equation 1
VT 1/8  C1
25  180 
1/8
 C1
C1  47.846
25
From equation  2 
VT 1/ 5  C2
25  180 
1/ 5
 C2
C2  70.63
From equation 1
32  T 1/ 8  47.846

C1  47.846 
T  24.97 min
From equation  2 
32  T 1/ 5  70.63
T  52.38 min
For 32m/min cutting speed, second equation
i.e.VT1/5  C2 gives better life.
Ans.
9. In A Tool Wear Test With High-Speed Steel Cutting Tool, The Following Data
Were Recorded.
Tool Life
30min
2min
Cutting Speed
25m/Min
70m/Min
Compute The Taylor’s Equation
[M.U. Oct ‘97]
Given Data:
T1 = 30min
V1 = 25m/Min
T2 = 2min
V2 = 70m/Min
To Find:
Compute The Taylor’s Equation.
Solution:
Taylor’s Equation Is Vtn = C
V1T1n  V2T2 n
25  30n  2  70n
26
25  70 
n
   n   2.333
2  30 
 25 
n log  2.333  log  
 2 
n  2.98
Taylor ' s equation is 30   25
2.98
 2   70 
2.98
Ans.
10. The Following Data From An Orthogonal Cutting Test Is Available
Rank Angle
= 150
Chip Thickness Ratio
= 0.383
Uncut Chip Thickness
= 0.5mm
Width Of Cut, B
= 3mm
Yield Stress Of Material In Shear
= 280 N/Mm2
Average Coefficient Of Friction On The Tool Face = 0.7
Determine The Normal And Tangential Forces On The Tool Face. [M.U.Oct 95]
Given Data:
 = 15o
r  0.383
t1  0.5mm
b  3mm
  280 N / mm2
  0.7
To Find:
Normal Force And Tangential Force
Solution:
 r cos  
 0.383cos15 
 tan 1 

1  r sin  
1  0.383sin15 
  tan 1 
  22.3o
Shear stress,  =
Fs
As
27
A1
bt
 1
sin  sin 
3  0.5
As 
 3.948mm 2
sin 22.32
Fs
280 
3.948
Fs  1105.63 N
As 
  tan 
  tan 1     tan 1  0.7 
  34.99  35o
Fs
cos 
        22.3  35  15
F
  42.3o
1105.63
 1494.65 N
cos 42.3
Tangential force or cutting force,
F
F2  F cos    
= 1494.65cos  35-15 
F2  1404.5 N
Ans.
Normal force or feed force,
Fx  F 2  Fz2

F= Fz2  Fx2

= 1494.652  1404.52
Fx  511.2 N
Ans.
Result:
1. Normal force, Fx  511.2 N
2.Tangential force Fz  1404.5 N
28
UNIT – II
CENTRE LATHE AND SPECIAL PURPOSE LATHES
PART – A
Lathe
Lathe Is A Machine Which Removes The Metal From A Piece Of Work To The
Required And Size.
Hold A Workpiece In A Centre Lathe
Between The Two Centers Of Head Stock And Tail Stock
Swing Diameter
The Largest Diameter Of Work That Will Revolve Without Touching The Bed
And Is Twice The High Of The Center Measured From The Bed Of The Lathe.
The Specification Of Typical Lathe
1. The Length Of Bed
2. Maximum Distance Between Dead And Live Centers.
3. Type Of Bed I.E. Straight, Semi Gap Or Gap Type.
4. The Height Of Centers From The Bed
5. Swing Over The Bed
6. Swing Over The Cross-Bed
7. Width Of The Bed
8. Spindle Bore
9. Spindle Speed
10. H.P. Of Main Motor And Rpm
11. Number Of Spindle Speeds
12. Spindle Nose Diameter
13. Feeds
14. Floor Space Required.
29
The Tool Moves Perpendicular
Produce_____________
To
The
Axis
Of
The
Work
To
Flat Surface
The Various Operations Can Be Performed On A Lathe
1. Turning
2. Facing
3. Forming
4. Knurling
5. Chamfering
6. Thread Cutting
7. Drilling
8. Boring
9. Recessing
10. Tapping
11. Grooving Etc.
The Principle Parts Of A Lathe
1. Red
2. Headstock
3. Tailstock
4. Carriage
5. Cross-Slide
6. Tool Post
The Main Requisites Of A Lathe Bed
1. Red
4. Carriage
2. Headstock
5. Cross-Slide
3. Tailstock
6. Too, Post
The Main Requisites Of A Lathe Bed
The Lathe Bed Should Be Very Strong To Withstand Cutting Forces And Vibrations
During Machining.
30
Provisions Are Made To Accommodate Other Parts Of A Lathe On The Bed
Guide Ways
The Uses Of Headstock
1. Headstock Carries A Hollow Spindle With Nose To Hold The Work Piece.
2. To Mount The Driving And Speed Changing Mechanisms.
The Types Of Headstock
1. Back Geared Type
2. All Geared Type
The Name Of The Center Mounted On The Tailstock.
Dead Center
The Main Difference Between Live Center And Dead Center
I. Live Center Drives And Rotates Along With The Work Pieces.
Ii. Dead Center Just Supports The Other End Of The Work Piece.
The Names Of Any Four Lathe Accessories.
Lathe Centres, Catch Plates, Carries, Chucks, Mandrels And Rests.
The Taper Is Formed On The Work Piece By Using Tailstock
The Upper Body Of Tailstock Can Be Moved Towards Or Away From The
Operator.
The Position Of A Carriage.
The Carriage Is Mounted In Between Headstock And Tailstock.
The Various Parts Mounted On The Carriage.
31
a.
b.
c.
d.
Saddle
Compound Rest
Cross Slide
Tool Post
The Shape And Position Of Saddle.
H Shaped Component Is Fitted Across The Lathe Bed.
Holes Drilled In A Center Lathe
First, The Dead Center Of The Tailstock Is Replaced By A Drill Bit. The
Longitudinal Movement Of The Tailstock Is Locked After Setting The Approach Of
Drill. Finally, The Hand Wheel Of The Tailstock Is Rotated For Making The Hole On
The Specimen.
Compound Rest
A Member Or Part Which Is Mounted On The Top Of The Cross Slide Having A
Base Graduated In Degrees.
For Making Taper Portion Of Bigger Diameter At The Left End On The Given
Work Piece. How The Tool Post Is Tilted
For Making Taper Portion Of Bigger Diameter At The Left End, The Tool Post
End Should Be Set Towards The Bigger Diameter.
The Four Types Of Tool Post
1. Single Screw Tool Post
3. Four Bolt Tool Post, And
2. Open Side Tool Post
4. Four Way Tool Post
The Cutting Tool Is Fixed On A Single Screw Tool Post And How Can Vary Tool
Height
32
A Single Screw Tool Is Used To Hold Only Single Tool, Which Are Clamped By
Clamping Screw. The Tool Height Can Be Varied By Adjusting A Rocker Placed On
The Tool Post.
The Provision For Adjusting The Tool Height In Open-Side Tool Post.
Parallel Strips Packing Is Used To Adjust The Tool Height.
The Use Of Four-Bolt Tool Post
Two Tools May Be Held In Position By Two Straps And Four Bolts.
Type Tool Post Maximum Number Of Tools Can Be Mounted How Many
In Four Way Tool Post, Maximum Four Tools Can Be Mounted.
Apron
Apron Is An Integral Part Of Several Gears, Levers And Clutches Which Are
Mounted With The Saddle For Moving The Carriage Along With Lead Screw While
Thread Cutting.
Type Of Mechanism Is Used For Giving Automatic Feed To The Tool While
Thread Cutting
Half Or Split Nut Mechanism.
Four Types Of Lathes
1. Engine Lathe
4. Semi-Automatic Lathe
2. Bench Lathe
3. Tool Room Lathe
5. Automatic Lathe.
Bench Lathe
33
A Small Size Lathe Which Has All Parts Similar To A Center Lathe Which Can
Be Mounted On A Bench.
Tool Room Lathe.
A Tool Room Lathe Consists Of All The Necessary Attachments Required For
Accurate And Precision Machining.
Semi-Automatic Lathe
A Lathe In Which All The Machining Operations Are Performed Automatically
But Loading And Unloading Of Work Piece, Coolant On Or Off Are Performed
Manually.
Two Types Of Semiautomatic Lathe
1. Capstan Lathe
2. Turret Lathe
The Semi-Automatic Lathe Differs From Center Lathe
A Hexagonal Turret Head Replaces Tailstock.
The Advantages Semi-Automatic Lathes
1. Production Time Is Minimized
2. Accuracy Will Be High
3. Production Rate Is Increased
Automatic Lathe
In Addition To Automatic Machining Operations Loading And Unloading Are
Also Performed Automatically.
Special Purpose Lathe.
34
The Lathes Which Are Specially Designed For Carrying Out Specific Operations
Only.
Copying Lathe
The Tool Of This Lathe Follows A Template Or Master Through A Stylus Or Tracer.
The Various Types Of Headstock
1. Back Geared
2. All Geared.
Feed.
Feed Is Defined As The Movement Of The Tool Relative To The Work And The
Work Piece By Form Tool.
Various Feed Mechanism Used For Obtaining Automatic Feed.
1.
2.
3.
4.
Tumbler Gear Mechanism
Quick Change Gearbox.
Tumbler Gear-Quick Change Gearbox
Apron Mechanism
Four Work Holding Devices.
1.
2.
3.
4.
Chucks
Centres
Face Plate
Angle Plate.
The Use Of Chucks.
Chucks Are Use To Hold The Work Piece Of Small Length And Large Diameter.
The Various Types Of Chucks
35
5. Three Jaw Chuck (Or) Self Centering Chuck.
6. Four Jaw Chuck Or Independent Chuck
7. Magnetic Chuck
The Application Of Air Operated Chuck
Heavy Work Pieces Are Mounted With The Help Of Air-Operated Chucks.
Because They Will Require More Power To Hold The Work Piece.
The Use Of Mandrels
Mandrels Are Used For Holding Hollow Work Pieces.
Steady And Follower Rest.
Steady Rest: It Is Fixed On Bed Way’s Of The Lathe By Clamping The Bolts.
Followers Rest: It Is Mounted On The Saddle And Moves Together With The Tool.
The Different Operations Performed On A Lathe
1. Centering
3. Rough Turning
5. Shoulder Turning
7. Chamfering
2. Straight Turning
4. Finish Turning
6. Facing
8. Knurling Etc.
Filing Operation.
Filling Is The Process Of Removing Bars, Sharp Corners And Feed Marks On A
Work Piece By Removing Very Small Amount Of Metal.
Forming Operation
Forming Is The Process Of Producing Concave, Convex And Any Irregular
Shape.
The Process “Grooving”.
36
Grooving Is The Process Of Reducing The Diameter Of The Work Piece Over A
Very Narrow Surface.
Parting Off Is An Operation Of _________.
Cutting A Work Piece After Machining
“Eccentric”
The Axis Of One Cylinder Is Off-Set With The Axis Of Other Cylinder.
Drilling Operation
Drilling Is The Operation Of Producing Cylindrical Hole In A Work Piece.
Reaming And Boring Operation
Reaming: It Is The Operation Of Finishing And Sizing Of Already Drilled Hole.
Boring: It Is The Process Of Enlarging A Already Drilled Hole.
Milling Operation
The Operation Of Removing Metal By Using Rotating Cutter Having Multiple
Cutting Edges Is Known As Milling.
Tapping
Tapping Is The Operation Of Forming Internal Thread Of Small Diameter By
Using A Multipoint Tool.
“Taper”.
Taper Is Defined As A Uniform Change In The Diameter Of A Work Piece
Measured Along Its Length.
“Conicity”.
37
The Ratio Of The Difference In Diameters Of The Taper To Its Length.
Dd
K
l
Where, D = Bigger diameter
d = Smaller diameter
l  Length of the work piece
Various Methods For Taper Turning Operation.
a.
b.
c.
d.
Form Tool Method
Tailstock Set Over Method
Compound Rest Method
Taper Turning Attachment Method
Formula For Calculating Tailstock Set Over Distance.
D-d
 L  L tan 
2l
Where, D = Bigger diameter
d = Smaller diameter
l  Length of the work piece
L=Distance between live center to dead center.
Set over, S =
Formula For Calculating Taper Turning Angle By Compound Rest Method.
Dd
2l
Where, D = Bigger diameter
tan  
d = Smaller diameter
l = Length of the work piece
Determine The Angle At Which The Compound Rest Will Be Swiveled When
Cutting A Taper On A Piece Of Work Having The Following Dimensions.
e. Outside Diameter – 60mm
f. Length Of The Tapered Portion 80mm And
g. Smallest Diameter = 20mm
38
Given Data:
D = 60mm
L = 80mm (Length Of Tapered Portion)
D = 20mm
C
Solution:
D-d
In this case, Sin =
2l
60-20
=
 0.3625
2  80
 = 21o 15'
80
20
A

B
Thread Cutting Operation
Thread Cutting Is The Operation Of Producing Continues Helical Groove On A
Cylindrical Work Piece.
The Number Of Teeth On Various Change Gears Be Calculated
Driver teeth
Teeth on spindle gear

Driven teeth Teeth on headscrew gear
Pitch to be cut on work

Pitch of lead screw
“Thread Catching”.
The Process Of Following The Same Path Of The Tool When It Has Traveled In
The Previous Cut Is Called As Thread Catching Or Thread Picking-Up.
Taper Of A Given Work Piece Having ¼ Conicity.
tan  
Dd 1 1 1
  
2l
2 4 8
61. Write Down The Formula To Find The Following Parameters.
39
L
f N
2. Total length of tool travel = l  x  y
1. Machining time =
Total machining allowance
Material removal per cut
Where, L = Total length of work piece,
3. Number of passes or cuts =
x  lengthoftoolapproach
f  Feed ,
N = speed and
y = Over run,
The Important Requires Of Capstan And Turret Lathe.
1. Bed
2. Head Stock
4. Saddle And Cross Slide
3. Turret Head
The Various Types Of Cross-Slide
1. Reach Over Type
2. Side Hung Type.
The Various Types Of Headstock For Turret Lathes
1. Back Geared
2. All Geared
3. Pre-Selective Stock
The Special Provision Made In Pre-Selective Headstock
The Speed Changing For Different Machining Operation Can Be Done By Simply
Pushing A Button Or Pulling A Lever To Select The Speed Of The Next Operation In
Advance.
Type Of Mechanism Is Used For Indexing The Turret Head For The Next
Operation
40
Geneva Or Indexing Mechanism
Two Specification Of Capstan And Turret Lathe.
1. Number Of Spindle Speeds
2. Number Of Feeds For The Turret Of Saddle
The Advantages Of Turret Lathe Over Capstan Lathe.
1. Heavier And Larger Work Piece Chucking Can Be Done
2. More Rigid, Hence It Withstands Heavy Cuts.
Four Work Holding Devices.
1. Collets
3. Fixtures
2. Chucks
4. Power Chucks
Four Tool Holding Devices.
1.
2.
3.
4.
Multiple Cutter Holder.
Offset Cutter Holder
Sliding Cutter Holder.
Knee Tool Holder.
Collapsible Tap
Collapsible Tap Is Used For Making Internal Threads. During Making Threads,
The Cutting Edges Of The Tap Collapses To Reduce Its Overall Diameter.
Bar Stop
Bar Stop Is Nothing But Workshop. It Is Used For Setting The Required Length
Of The Work Piece.
Tooling
Planning Of Operation Sequence And Preparation Of Turret Or Capstan Lathe
Are Termed As Tool-Layout Or Tooling.
41
Three Stages Of A Tool-Layout
1. Planning And Scheduling
2. Detailed Sketching Of Various Machining Operation Sequence
3. Sketching The Plan Showing Various Tools.
Various Types Of Special Purpose Lathes
1. Semi-Automatic Lathes
2. Car Wheel Turning Lathes
3. Camshaft Turing Lathes
Different Drives Used In Copying Lathes
1. Mechanical Drives
2. Air Drives
3. Hydraulic Drives
The Components That Can Be Turned On A Copying Lathe
1. Camshaft
2. Crankshaft
3. Journal Bearings
Automatic Machine
Automatic Machine Or Simply Automats Are Machines Tools In Which All The
Operations Required To Finish Off The Work Piece Are Done Automatically Without
The Attention Of An Operator.
Four Advantages Of Automatic Lathes.
1.
2.
3.
4.
Mass Production Of Identical Parts.
High Accuracy Is Maintained
Time Of Production Is Minimized
The Bar Stock Is Fed Automatically.
Automat.
1. Classification According To The Type Of Work Material Used
42
a. Bar Stock Machine
b. Chucking Machine
2. Classification According To The Number Of Spindles
A. Single Spindle Automats
b. Multi Spindle Automats
3. Classification According To The Arrangements Of Spindles
a. Horizontal Spindle Type
b. Vertical Spindle Type
4. Classification According To The Feed Control
A. Single Cam Shaft Rotating At Constant Speed
B. Single Cam Shaft With Two Speeds
C. Two Cam Shaft
5. Classification According To The Use
A. Single Purpose Machine
B. General Purpose Machine
The Cam Draw Power From Main Spindle
The Cam Draws The Power From The Main Spindle Through A Set Of Gears
Called Cyclic Time Change Gears.
The Tools Used In Turret Of Single Spindle Automatic Lathes
Form Tools, Turning Tools And, Drilling Tools
The Other Names Spindle Automatic Lathes.
Screw Cutting Machines
The Types Of Single Spindle Automatic Lathes
1. Automatic Cutting Off Machine
2. Automatic Screw Cutting Machine
3. Swiss Type Automatic Screw Machine
Threads And Machining Holes Are Cut In Automatic Cutting Off Machine
To Cut Threads And Machining Holes, Special Attachments Are Used.
43
The Purpose Of Providing Lead Can In Single, Spindle Automatic Screw Cutting
Machine
The Turret Slide Travel Is Controlled By A Lead Cam. The Lead Cam Gives A
Slow Forward And Fast Return Movement To The Turret Slide.
The Applications Of Single Spindle Automatic Screw Cutting Machine.
It Is Used For Producing Small Jobs, Screws, Stepped Pins, Taper Pins, Bolts Etc.
The Advantages Of A Sliding Head Automatic Lathes
The Advantages Of A Sliding Head Automatic Lathe Is That Long Slender Work
Pieces Can Be Machined With Very Good Surface Finish, Accuracy And
Concentricity In Sliding Head Automatic Lathes.
The Four Major Parts Of Swiss Type Automatic Lathes
1. The Sliding Headstock Through Which The Bar Stock Is Passed And Gripped
By A Carbide-Lined Guide Bush.
2. The Camshaft, Controlling The Bar Stock And Cutting Tool Movements.
3. The Tool Bracket Supporting Five Tool Slides And A Bush For Stock
4. Auxiliary Attachments For Performing Various Operations Such As Knurling,
Drilling, Tapping, Screwing, Slotting And Recessing Etc.
The Advantages Of Swiss Type Screw Cutting Machine.
1.
2.
3.
4.
5.
6.
7.
8.
It Has Five Tool Slides
Wide Range Of Speeds
Rigid Construction
Micrometer Tool Setting
Interchangeability Of Cams
Simple Design Of Cams
Tolerance Of 0.005 Tom0.0125mm Are Obtained
Numerous Working Stations
44
The Principle Of Multi Spindle Automats.
The Principle Advantage Of The Multi Spindle Automat Is That It Has A Tool
Slide Working On The Jobs On All Spindles Simultaneously
Multi Spindle Automats.
Multi-Spindle Automatic Lathes Are Classified As Follows:
1. According To The Type Of Work Piece (Stock) Used
c. Bar Type Machine
d. Chucking Type Machine
2. According To The Arrangement Of Spindle
a. Bar Type Machine
b. Chucking Type Machine
3. According To The Principle Of Operation
a. Parallel Action Type
b. Progressive Action Type
The Other Name Of Parallel Action Multi Spindle Automats.
Multi-Flow Machine
The Parallel Action And Progressive Action Multi Spindle Automatic Lathes.
Sl.No
1
2
3
4
Parallel Action Machine
Same Operation Is Done On All
Jobs In All The Spindles
In One Cycle, The Number Of
Components
Produced
Simultaneously Is Equal To The
Number Of Spindles
Progressive Action Machine
Different Operation Are Done On Jobs At
Each Station One After Another
It Is Not So, (I.E) The Number Of
Components Produced In One Cycle Is Not
Equal To The Number Of Spindles. For Every
Indexing Of Component (Spindle) One
Component Is Produced
Rate Of Production Is Very High
Rate Of Production Is Moderate
If Anything Goes Wrong In One If Anything Goes Wrong In One Station, The
Station, The Production In That Production Is Completely Affected In All The
45
Particular Station Only Is Affected
Stations.
46
Problem 1.
The Minimum And Maximum Speed Of A Head Stock Spindle Of A Lathe Are 50
Rev/Min And 1500 Rev/Min. The Number Of Speeds Available Is 18. Find The
Intermediate Speeds.
Given Data:
Nmin = 50rev/Min
Nmax = 1500rev/Min
Z = 16
Solution:
Step Ratio Is Given By The Formula
1
1
 N  z 1  1500 161
   max   

 50 
 N min 
=  30 
0.667
  1.2545
The speeds are 50,   50,  2  50,......1500. Ans.
i.e.,50,62,72,78,69,98.7,23.8,155.36,195,....1500.
2. Calculate The Gears For Cutting Metric Threads Of The Following Pitches.
I. 4mm Pitch
Ii. 5.25mm Pitch
The Lead Screw Of The Lathe Contains 6tpi. The Lathe Supplied With 20 To 120
Teeths In Steps Of 5 And An Additional Gear Wheel Of Having 127 Teeth.
Solution:
For metric threads,
Driver teeth 5np

Driventeeth 127
47
where, n = number of threads per inch i.e. TPI
p = Pitch of the thread to be cut
i. 4mm pitch
Driver teeth 5np 5  6  4 120



Ans.
Driven teeth 127
127
127
The Gear Train Will Consist Of 120 Teeth On The Spindle Gear And 127 Teeth On
The Lead Screw.
Ii. 5.25mm Pitch
21
5 6
Driver teeth 5np 5  6  5.25
4



Driven teeth 127
127
127
105  6 105 60
=


Ans.
4 127 40 127
( Numerators And Denominators Are Multiplying By 10)
For 5.25mm Pitch, Compound Gear Train To Be Used With 105 Teeth On
Spindle Gear And 127 Teeth On The Intermediate Gear, 60 Teeth Intermediate Gear
Drives A 40 Teeth Gear On The Lead Screw.
Problem 3
Calculate The Cutting Speed On A Piece Of Mild Steel Of 100mm Diameter
And Rotting At 300rpm.
Given Data:
D = 100mm
N = 300rpm
Solution:
Cutting speed, V =
 DN

 100  300
1000
1000
= 94.25m/min
4. Find The Gear Train For Cutting 2mm Pitch Thread On A Lathe Having Lead
48
Screw Of 10mm Pitch.
Solution:
Driver teeth
Pitch of the work

Driven teeth Pitch of the leadscrew
2
2 10
20
=


10 10 10 100
The Gear Train Consists Of 20 Teeth On The Driver And 100 Teeth On Driven
(Lead Screw Gear) To Be Used Without Intermediate Gear.
Problem 5
Determine The Required Change Gears For Cutting 1.25mm Pitch Thread
On A Lathe Having Lead Screw Of 8mm.
Solution:
Driver teeth
Pitch of the work

Driventeeth Pitch of the leadscrew
1.25 1.25  4 5 5 1
=


 
8
8 4
32 8 4
5 10 1 20 50 20
=

 
8 10 4  20 80 80
The Compound Gear Train Is To Be Used Since 32 Teeth Gear Is Not
Available In The Standard Set Of Gears Which Are Supplied. The Driver Gears Will
Have 50 And 20 Teeth And Driven Gears Of Both 80 Teeth
Problem 6
The Pitch Of The Lead Screw Of A Lathe Is 6mm. If The Pitch Of The
Thread To Be Cut Is 1.5mm, Find The Change Gear Wheels. Available Gear
Wheels Are 20 To 120 In Steps Of 5. Draw A Sketch Showing The Gear
Arrangement.
Given Data:
Pitch Of The Lead Screw = 6mm
Pitch Of The Thread To Be Cut = 1.5mm
Available Gear Wheels Are 20 To 120 In Steps Of 5
Solution:
49
Dirver teeth Pitch of the thread to be cut

Driven teeth
Pitch of the leadscrew
1.5 1.5  4 6 6 1



 
6
6  4 24 4 6
6  5 1 20 30 20

 
4  5 6  20 20 120
Compound Gear Train To Be Used For Making The Above Thread. The
Driver Gears Will Have 30 And 20 Teeth. The Driven Gears Will Have 20 And 120
Teeth.
Problem 7
Calculate The Time Taken To Turn A Brass Component 75mm Diameter
And 125mm Long If The Cutting Speed Is 52m/Min And The Feed Is 0.8mm/Rev.
Only One Cut Is To Be Considered.
Given Data:
D = 75mm
L = 125mm
V = 52m/Min
F = 0.8mm/Rev
Solution:
L
 DL
  75 125 
 DN 


 V

fN 1000V f 1000  52  0.8 
1000 
=0.707min=42.42sec
Time, Tm 
Problem 8
Calculate The Time To Face A Work Piece Of 80mm Diameter. The Spindle
Speed Is 115rpm And Cross Feed Is 0.4mm/Rev
Given Data:
D = 80mm
N = 115rpm
F = 0.4mm/Rev
Solution:
50
L
fN
L  D / 2  80 / 2  40mm
40
Tm 
 0.869 min  52sec
0.4  115
Tm 
Problem 9
Calculate The Number Of Teeth On Change Gears To Cut A Mild Start
Thread Of Having 4 Starts And Pitch 1.25mm. The Pitch On The Lead Screw Is
8mm.
Given Data:
N=4
P = 1.25
Pitch Of The Lead Screw = 8mm
Solution:
Pitch on the work = n  P=4 1.25=5mm
Driver teeth
Pitch of the work
5


Driven teeth Pitch of the lead screw 8
5 5 25
=  
8 5 40
Therefore, The Driver Will Have 25 Teeth And Driven Will Have 40teeth.
Problem 10
A Shaft Of Diameter 60mm Is To Be Turned On A Lathe At A Cutting
Speed Of 45m/Min. Find The Required Rpm Of The Shaft.
Given Date:
V = 45m/Min
D = 60mm
To Find:
Speed In Rpm
Solution:
51
V
 DN
1000
1000  45
N
  60
 238.7
 239rpm.
Problem 11
Calculate The Time Required For One Complete Cut On A Piece Of Work
Having 250mm Long And 40 Mm Diameter. The Cutting Speed Is 32m/Min And
The Feed Is 0.4 Mm/Rev.
Given Data:
L = 250 Mm
D = 40mm
V = 32m/Min
F = 0.4mm/Rev
Solution:
 DN
V
1000
1000  32
N
 255rpm
  40
Number of revolution for one complete cut, Y
L 250
Y= 
 625rev
f
0.4
Y 625
Time required for one complete cut,

 2.45 min
N 255
TOOLING
52
1. Simple Tool Layouts
Turret And Capstan Lathes Are Mainly Used For Machining Workpieces On
A Rapid Rate. Before Starting The Production, The Following Works Are Carried
Out
1.
2.
3.
4.
5.
Selection Of Tools
Designing Of Special Tools
Selection Of Speeds
Selection Of Feeds
Setting The Required Length Of Work Piece And Tool Travel Length.
These Planning Of Operation Sequence And Preparation Of Turret Of Capstan
Are Termed As Tool-Layout. The Accuracy And Cost Of Product Are Largely
Dependent On An Efficient Tool Layout. The Tool Layout Mainly Consists Of Three
Stages.
1. Planning And Scheduling Stage: Preparation Of Operation Sheet With Order
Of Operation.
2. Detailed Sketching Of Various Stages Of Machining Operations In Sequence
Of Operations.
3. Sketching The Plan Showing The Various Tools Into The Hexagonal Turret
Face And Cross Slides With Proper Sequence.
2. Step By Step Procedure For Preparing Tool Layout Of Turret And Capstan Lathe
In Detail As Below
1. The Component To Be Machined Is Thoroughly Studied And The Required
Total Length Of The Work Is Calculated.
2. The Number Of Operations Involved In The Component Starting From The
Right End Is Roughly Listed.
3. From The Rough List Of Operations, The Proper Operation Sequence Is
Decided.
4. Various Tools According To The Sequence Of Operations Are Selected.
5. The Selected Tools Are Fitted Either Or Hexagonal Turret Or On Cross-Slide
According To The Operation Sequence.
53
6. The Proper Cutting Speeds, Feeds And Depth Of Cut For Each And Every
Operation Are Selected.
7. The Total Time Required Per Piece Is Determined. The Total Time Includes
The Following Time Terms.
A. Total Machining Time Of Each And Every Operations.
B. Idle Time Between Successive Operations And
C. Time Required For Loading And Unloading The Components.
8. The Detailed Drawing Of The Work Piece Is Drawn Along With The Turret
Tools And Cross-Slide Tools In Position.
The Above Procedure Can Be Recorded Either On A Plain Paper Or On A
Simplified Process Planning Sheet Called Operation Sheet Or Process Layout.
Before Doing The Actual Layout, The Tool Designer Should Be Familiar In
The Filed Of Capstan And Turret Lathes Tools, And Operations.
3. Solved Examples On Tooling.
Problem 12
A Tool Layout Is Prepared For The Manufacture Of Square Headed Bolt
From A Square Bar Stock Using A Turret Lathe As Shown In Figure.
Solution:
Stage I:1. The Component Drawing Is Drawn
2. The Total Length Of The Work Is Calculated And 10mm Is Added To Provide
Clearance.
3. The Number Of Operations Involved Is Roughly Listed.
4. The Sequence Of Operation Is Assigned.
5. The Proper Machine Of 75mm Turret Lathe Is Selected.
6. The Proper Material Of Mild Steel Square Bar Is Selected.
7. All The Tools And Equipments As Per Operation Sequence Are Collected
And Fitted On Turret Faces Or On Cross Slides As Per Out Convenience.
Stage Ii:-
54
1. The Tool Layout Is Drawn As Shown In Figure
[Note: Number Tools Fitted In The Turret Face Are Only Four. So, For Providing
Uniform Balancing Tools Are Arranged Like The First Two Are In Successive Faces
And Other Two Are In Next Successive Faces By Leaving One Face Left To Free]
Stage Iii:Tooling Schedule Chart (To Machine Square Bolt)
Machine : 75mm Turret Lathe
Material: Square Mild Steel Bar
Operation
Sequence
1.
2.
3.
4
5
Description Of Operation
Tool Position
Holding The Square Bar In Collet
And Setting The Required Length
Of 100mm (90+10)
Turn To 20mm Diameter To A
Length 70mm (From The Right
End)
Form The Right End Of The Bolt
Turret Positions
Tools
Bar Stop
Turret Position Roller Steady
–2
Turning Rod
Box
Turret Position Roller Steady Bar
–3
Ending Tool.
Make The External Thread Turret Position Self
Opening Die
Cutting Of 20mm Diameter To A – 4
Head With Chases Of
Length Of 40mm (From The
20mm
Right End)
Chamfering The Bolt Head.
Front
Cross Chamfering Tool
55
Slide Tool Post1
Rear Tool Post
Parting Tool Is Placed
In Inverted Position
(Making The Rotation
Of
Work
Anticlockwise
With
Respective To Tool)
Parting Off The Work Piece
6.
Description Of Operations To Be Performed
I. Setting The Bar Stop:
The Bar Stop (1) Is Set At The Distance Of 100mm From The Collect Face By
Using Slip Gauge. An Extra Length Of 10mm Is Allowed For Parting Off (4mm) And
Clearance Off The Collect Face (6mm). This Clearance Is Allowed To Penetrate The
Parting Tool Deep Into The Work Piece Without Any Interface.
Ii. Setting Of The Roller Steady Box Turning Rod:
This Tool Is Set On Turret Face Of 2. This Tool (2) Is Used For Turning The
Work Piece To 200mm Diameter And 80mm Long From The Right End.
Iii. Setting Of Bar Ending Tool:
This Tool Is Set (3) On Fourth Turret Face But Turret Position-3. This Is Used
To Chamfer The Right End Of The Work Piece.
Iv. Setting Self Opening Die Head:
This Tool (4) Is Set On The Fifth Face Of The Turret. The Proper Blades Of
Chasers Are Selected And Fitted Into The Die Head To Cut A Thread Of 20mm
Diameter.
V. Setting Of Chamfering Tool:
This Tool (5) Is Set On The Cross-Slide Front-End Position-1 Used To Chamfer
The Bolt Head Edges By Giving Cross Feed.
56
Vi. Setting Of Parting Tool:
This Tool Is Set On The Rear End Of Cross-Slide. It Is Used To Part Off The
Work Piece After Completing All Operations.
Note: Distance Of Each Tool Movement Is Set By Positioning The Stop With The
Help Of Slip Gauges]
Problem 13
Draw The Tool Layout For Manufacturing Knurled Screw And Nut As
Shown In Figure On Turret Lathe.
Solution:
Stage I:
1. The Component Drawing Is Drawn.
2. The Total Length Of The Work Is Calculated And 10mm Is Added To Provide
Clearance
3. The Number Of Operations Is Listed
4. The Sequence Of Operation Is Listed
5. The Proper Machine Of 75mm Turret Lathe Is Selected.
6. The Proper Material Of Mild Steel Square Bar Is Selected.
7. All The Tools And Equipments As Per Operation Sequence Are Collected
And Fitted On Turret Faces Or On Cross-Slides As Per Our Convenience.
Stage Ii:1. The Tool Layout Is Drawn As Shown In Figure
57
Note: Number Tools Fitted In The Turret Face Are Only Four. So, For Providing
Uniform Balancing Tools Are Arranged Like The First Two Are In Successive Faces
And Other Two Are In Next Successive Faces By Leaving One Face Left To Free]
Stage Iii:Tooling Schedule Chart (To Machine Given Component)
Machine: 75mm Turret Lathe
Material: Square Mild Steel Bar.
Operation
Sequence
1.
2.
3.
4.
5.
Description Of Operation
Tool Position
Holding The Square Bar In
Collect And Setting The
Required Length Of 47mm
(37+10)
Turn To 10mm Diameter To A
Length 37mm (From The Right
End)
Turn To 5mm Diameter And
Form The Right End Of The
Bolt For A Length Of 25mm
And Form The End
Make The External Thread
Cutting Of 5mm Diameter To
A Length Of 23mm(From The
Right End)
Knurling On The Required
Length
58
Tools
Turret Position. 1
Bar Stop
Turret Position. 2
Roller Steady BoxTurning Rod.
Turret Position. 2
Roller Steady Bar
Ending Tool
Turret Position. 3
Knurling Tool Holder
With Knurls
Turret Position.4
Knurling Tool Holder
With Knurls
6.
Chamfering The Bolt Head On
10mm Diameter
7.
Parting Off The Screw
8.
9.
Drill And Face The Nut
Threading By Tap
Front Cross Slide
Tool Post Position
Rear Cross Slide.
1
Turret Position. 5
Turret Position.6
10.
Parting Off The Nut
Rear Tool Post
Chamfering Tool
Parting Tool
Drill And Facing Tool
Tap
Parting Tool Placed In
Inverted Position (For
Making The Rotation
Of Work Anticlockwise
With Respective To
Tool Movement)
Description Of Operations To Be Performed
I. Setting The Bar Stop:
The Bar Stop (1) Is Set At The Distance Of 47mm From The Collect Face By
Using Slip Gauge. An Extra Length Of 10mm Is Allowed For Parting Off (4mm) And
Clearance Off The Collect Face (6mm). This Clearance Is Allowed To Penetrate The
Parting Tool Depth Into The Work Piece Without Any Inference.
Ii. Setting Of The Roller Steady Box Turning Rod:
This Tool Is Set On Turret Face Of 2. This Tool (2) Is Used For Turning 10mm
Diameter To A Length 37mm (From The Right End)
Iii. Setting Of The Roller Steady Box Turning Rod:
This Tool Is Set On Turret Face Of 2. This Tool (3) Is Used For Turning 5mm
Diameter To A Length 25mm (From The Right End) And The Right End Of The
Work Piece Is Formed.
Iv. Setting Self Opening Die Head:
This Tool (4) Is Set On The Third Face Of The Turret. The Proper Blades Of
Chasers Are Selected And Fitted Into The Die Head To Cut A Thread Of 20mm
Diameter.
59
V. Setting Of Knurling Tool:
This Tool (5) Is Set On The Turret Position – 4 Which Is Used To Knurled
Portion On The Bolt Head.
Vi. Setting Of Chamfering Tool:
This Tool Is Set At The Front End Of The Cross-Slide Position2. It Is Used To
Chamfer 10mm Diameter.
Vii. Setting Of Parting Off Tool:
This Tool Is Set On The Rear End Of Cross-Slide Position 1. It Is Used To Part
Off The Screw.
Viii. Setting Of Drilling And Form Parting Off Tool:
This Tool Is Set On The Turret Position – 5 Used For Drilling And Facing The
Nut.
Ix. Setting Of Thread Chasers:
This Tool Is Set On The Turret Position – 6 Used To Make Internal Threads
Using Chasers.
X. Setting Of Parting Off Tool:
This Tool Is Set On The Rear End Of Cross-Slide Position 2. It Is Used To Part
Off The Nut.
[Note: Distance Of Each Tool Movement Is Set But Positioning The Stop With The
Help Of Slip Gauges]
60
14. Comparison Of Parallel Action And Progressive Action Multi-Spindle
Automatic Lathes
Sl
No.
1.
2.
3.
4.
5.
Parallel Action Machine
Progressive Action Machine
Same Operation Is Done On All
Jobs In All The Spindles
In One Cycle, The Number Of
Components
Produced
Simultaneously Is Equal To The
Number Of Spindles
Different Operations Are Done On Jobs At Each
Station One After Another.
It Is Not So,(I.E.) The Number Of Components
Produced In One Cycle Is Not Equal To The
Number Of Spindles. For Every Indexing Of
Component
(Spindle),One
Component
Is
Produced
Rate Of Production Is Very High Rate Of Production Is Moderate
If Anything Goes Wrong In One If Anything Goes Wrong In One Station, The
Station, The Production In That Production Is Completely Affected In All The
Particular Station Only Is Stations.
Affected.
Small Parts Of Simple Shapes Parts Of Complicated Shapes Can Be Produced.
Are Produced.
15. Comparison Of Single Spindle And Multi Spindle Automatic Lathes
Sl
No
1.
2.
3.
4.
5.
6.
7.
8.
9.
Single Spindle
Multi Spindle
There Is Only One Spindle
Only One Work Piece Is
Machined At A Time
The Rate Of Production Is Low
Machining Accuracy Is Higher.
Tool Setting Time Is Less
Tooling Cost Is Less
It Is More Economical For
Shorter As Well As Longer
Runs.
The
Time
Required
To
Produce One Component Is
The Sum Of All The Turret
Operation Times
Tools In Turret Are Indexed
There Are 2, 4, 5, 6, Or 8 Spindles
A Number Of Work Pieces Are Machined At A Time.
The Rate Of Production Is High
Machining Accuracy Is Lower
Tool Setting Time Is More
Tooling Cost Is More
It Is More Economical For Longer Rungs Only.
Time Required To Produces One Component Is The
Time Of The Longest Cut In Any One Spindle.
Work Pieces Held In Spindles Are Indexed (Progressive
61
Action Machine)
62
UNIT – III
MACHINE TOOLS
PART – A
One Pass Of The Cutting Tool.
The Combination Of One Forward And One Return Stroke Is Known As One Pass.
Number of passes =
Stock to be removed
Depth of cut
Stroke, The Speed Of The Ram Is Faster
Return Stroke.
Cutting Ratio Of A Shaper.
The Ratio Between The Cutting Stroke Time To Return Stroke Time,
Cutting stroke time
in 
Return stroke time
Two Types Of Quick Return Mechanism.
1. Hydraulic Drive Mechanism.
2. Crank And Slotted Lever Mechanism.
The Feed And Depth Of Cut Is Given To The Shaper
Feed Is Given By Rotating The Down Feed Screws Of Tool Head Depth Of
Cut Is Given By Rotating By Raising Or Elevating The Table.
The Various Types Of Flat Surface Produced On A Shaper.
1. Horizontal Surface
2. Vertical Surface
3. Inclined Surface
63
The Various Types Of Shaper According To Various Conditions
Generally, Shapers Are Classified As Follows.
1. According To The Type Of Driving Mechanism.
a. Crank Drive Type
b. Whit Worth Driving Mechanism Type.
c. Hydraulic Drive Type
2. According To The Position Of Ram.
a. Horizontal Shaper.
b. Vertical Shaper
c. Traveling Head Shaper
3. According To The Table Design
a. Standard Or Plain Shaper
b. Universal Shaper
4. According To The Type Of Cutting Stroke
a. Push Out Type
b. Draw Cut Type
The Other Type Of Shaper
1. Standard Or Plain Shaper
2. Universal Shaper
3. Draw Cut Shaper.
Four Shaper-Specifications.
1.
2.
3.
4.
Maximum Length Of Stroke
Type Of Driving Mechanism
Power Of The Motor
Speed And Feed Available
The Apron Is Fitted Away From The Machined Surface During Machining
The Apron Is Fitted Away From The Machined Surface To Avoid Rubbing Of
The Tool On The Work Surface.
64
The Important Part To Control And Divert The Flow Of Oil Into The Cylinder In
Hydraulic Drive.
Four – Way Valve.
Two Advantages Of Hydraulic Drive.
1. Higher Cutting To Return Ratio Can Be Obtained.
2. Infinite Range Of Cutting Speeds Is Available.
The Type Of Mechanism Followed On A Shaper And Have It Works.
Rock And Pinion Mechanism Is Used. The Rotary Motion Of Electric Drive Is
Converted Into Reciprocating Motion Of The Ram By Using Gears And Slotted Link.
The Precautions Of To Be Carried Out Before Machining Any Surfaces
1. Position Adjustment And
2. Stroke Length Adjustment.
Two Reasons For Making The Stroke Length Greater Than Work Length.
1. If The Crank Pin Is Adjusted In Such A Way From The Centre Of The Bull
Gear, The Rocker Arm Reciprocates For A Larger Distance, So, The Stroke
Length Is Increased.
2. The Stroke Length Should Always Be Greater Than The Work Length. I.E.
Some Amount Of Approach And Over Run Should Be Provided To The Tool
Movement.
The Types Of Feed
1) Hand Feed
2) Automatic Feed
Four Types Of Work Holding Devices.
1.
2.
3.
4.
Vice
Table
V-Block
Fixture
65
The Various Types Of Tool
The Tools Are Classified As Below:
1. According To The Shape.
a. Straight Tool.
b. Cranked Tool.
c. Goose Necked Tool.
2. According To The Direction Of Cutting
a. Left Hand Tool.
b. Right Hand Tool.
3. According To The Finish Required
a. Roughing Tool
b. Finishing Tool
4.
a.
b.
c.
d.
According To The Type Of Operation
Down Cutting Tool
Parting Off Tool
Squaring Tool
Side Recessing Tool.
5. According To The Shape Of The Cutting Edge.
a. Round Nose Tool
b. Square Nose Tool.
Any Four Operations Performed By A Shape.
1.
2.
3.
4.
Machining Horizontal Surfaces
Machining Vertical Surfaces
Machining Inclined Surfaces.
Machining Irregular Surfaces
The Tool Is Fitted On The Tool Head For Machining Inclined Surfaces
The Tool Is Set At Required Angle On The Tool Head Position And Stroke
Lengths Are Adjusted And Also Proper Cutting Speed And Feed Are Chosen. The
Apron Is Et Away From The Machining Surface. Depth Of Cut And Feed Are Given
The Same As That The Machining Vertical Surface.
66
The Dovetail Is Machined
To Make Dovetail, The Vertical Slide With Right Hand Tool Is At The
Required Angle On Right Side Of The Work. Just Giving Feed And Depth Of Cut,
The Right Side Dovetail Is Finished. Then The Vertical Slide With Left And Tool Is
Set The Required Angle On Left Side Of The Work. Here Also Just By Giving Feed
And Depth Of Cut. The Left Side Dovetail Is Finished.
The Various Types Of Recessing That Can Be Made By The Shaper
1. Grooves
2. Slots And
3. Key Ways
The Feed And Depth Of Cut Are Given To The Shaper While Machining Irregular
Surfaces
For Machining Irregular Surface, A Round Nose Tool Is Set On The Tool
Head. By Giving Both The Cross Feed And Vertical Feed At The Same Time The
Irregular Surface Is Obtained. The Cross Feed In Given Through The Table And The
Vertical Feed Is Given By The Tool Head, The Apron Is Fitted To Some Angle Away
From The Machined Surface To Avoid Rubbing Of The Tool On The Work During
Return Stroke.
Feed And Depth Of Cut.
1. Feed (F)
The Relative Movement Of Tool With Respect To The Work Piece Axis Is
Known As Feed.
2. Depth Of Cut (T):
Amount Of Metal Removed In One Revolution Or In Cut Is Known As Depth Of
Cut.
Write Down The Formula For Calculating No. Of Strokes And Passes Required In
A Shaper.
No. Of Strokes Required (SN)
67
The Ratio Between The Width Of The Work And Feed Per Stroke.
W
SN
f
Stock to be removed Sr
Number passes, n=

Depth of cut
r
The Metal Removal Rate.
Metal Removal Rate (W):
The Volume Of Metal Removed Per Unit Time.
Mmr (Or) W=Ftls
Planer Differs From A Shaper
In Planner:- The Work Reciprocates While The Tool Is Stationary.
In Shaper:- The Tool Reciprocates While The Work Is Stationary.
The Cross Feed And Vertical Feed Are Given In The Planner
The Cross Feed Is Given By Moving The Tool Head Along The Cross Rail
And The Vertical Feed Is Given By Moving Down The Tool.
The Uses Of Planer.
The Planer Is Used For Machining Heavy And Large Casting. Ex. Lathe Bed Guide
Ways, Machine Guide Ways Etc.
The Various Types Of Planners.
1.
2.
3.
4.
5.
Double Hosing Planer
Open Side Planer
Pit Planer
Edge Planer
Divided Table Planer
68
The Various Parts Of A Double Housing Planner.
1.
2.
3.
4.
5.
Bed
Table
Columns
Cross Rail
Tool Head
The Main Difference In Open Side Planer
The Only Difference In The Type Is Only One Vertical Column Is Provided
On One Side Of The Bed And Other Side Is Left Free.
The Main Advantages Of Using Pit Planer.
Heavy And Large Work Can Be Held And Machined Easily.
Special Provision Made In Edge Planner
Yes. A Platform Is Provided To Stand And Travel Along With It While Machining.
The Main Difference Made In Divided Table Planer
The Working Principle Is Similar To That Of A Standard Planer. But It Has Two
Reciprocating Tables.
Four Specifications Of Planer.
1.
2.
3.
4.
5.
Maximum Length Of The Table.
Total Weight Of The Planer.
Power Of The Motor.
Range Of Speeds And Feed Available
Type Of Drives Required.
The Function Of Clapper Block In A Planer
During Cutting Stroke, The Tool Block Fits Inside The Clapper Block Rigidly.
During The Return Stroke, The Tool Block Lifts Out Of The Clapper Block To Avoid
Rubbing Of The Tool On The Job.
The Various Types Of Quick Return Mechanism
69
1. Open And Cross Belt Drive
2. Electric Drive
3. Hydraulic Drive
The Various Quick Return Motion Mechanism Used In Slotter.
1. Whitworth Quick Return Mechanism.
2. Variable Speed Reversible Electric Motor Drive.
3. Hydraulic Drive.
The Difference Speeds Available In Slotter.
a. Longitudinal Feed
b. Cross Feed
c. Circular Feed
The Operations That Can Be Performed On A Slotter
I. Machining Flat Surface.
II. Machining Grooves, Slots, Key Ways.
III. Machining Irregular Surface.
“Milling Process”.
Milling Is The Process Of Removing Metal By Feeding The Work Past A Rotating
Multipoint Cutter.
The Specifications Of Milling Machine
1.
2.
3.
4.
5.
The Table Length And Width.
Maximum Longitudinal Cross And Vertical Travel Of The Table.
Number Of Spindle Speeds And Feeds.
Power Of Driving Motor.
Floor Space And Net Weight.
Milling Machine.
70
1. Column And Knee Types
a.
b.
c.
d.
e.
Plain Milling Machine
Vertical Milling Machine.
Universal Milling Machine
Ram-Type Milling Machine
Universal Milling Machine.
2.
a.
b.
c.
Bed-Type Milling Machine
Simplex Milling Machine.
Duplex Milling Machine.
Triplex Milling Machine.
3. Plano – Type Milling Machine
4. Special Purpose Milling Machine
a. Rotary Table Milling Machine
b. Drum Milling Machine.
c. Profile Milling Machine.
The Two Types Of Column And Knee Type – Milling Machine
i. Horizontal Type.
ii. Vertical Type.
The Principle Parts Of Horizontal Or Plain Milling Machine.
Base. Column, Knee, Saddle, Table, Over Arm, And Arbor.
The Various Movements Of Universal Milling Machine Table.
1.
2.
3.
4.
Vertical Movement – Through The Knee.
Cross Wise Movement-Through The Saddle.
Longitudinal Movement Of The Table.
Angular Movement Of The Table –By Swiveling The Table The Swivel Base.
Two Comparison Between Plain And Universal Milling Machine.
71
1. In Plain Milling Machine, The Table Is Provided With Three
Movements, Longitudinal, Cross And Vertical. In Universal Milling
Machine In Addition To These Three Movement There Is A Fourth
Movement To The Table. The Table Can Swiveled Horizontally And
Can Be Fed At Angle To The Milling Machine Spindle.
2. The Universal Milling Machine Is Provided With Auxiliaries Such As
Dividing Head, Vertical Milling Attachment, Rotary Table Etc. Hence It
Is Possible To Make Spiral, Bevel Gears Twist Drills, Reamers Etc On
Universal Milling Machine.
Universal Milling Machine Differs From Universal Milling Machine
This Is A Modified From Of Plan (Horizontal) Milling Machine. It Is Provided
With Two Spindles, One Of Which Is In The Horizontal Plane While The Other Is
Carried By A Universal Swiveling Head.
Bed Type Milling Machine.
The Bed Type Milling Machines Are Classified As Simplex, Duplex And Triplex
Machine.
The Different Ways For Machining Workpieces In Plano- Milling
a. By Moving The Table, The Cutters Rotating In Position.
b. By Keeping The Table Stationary And Feeding The Cutters By Moving The
Milling Heads.
c. By Moving The Table And The Milling Heads Simultaneously.
d. By Keeping The Table Stationary Mving The Cross-Rail Down Wards And
The Side Cutters Up And Down.
The Various Types Of Special Purpose Milling Machine
1) Rotary Table Or Continuous Milling Machine
2) Drum Type Milling Machine
3) Profile Or Count On Milling Machine
Four Important Types Of Work Holding Devices.
72
(a) N Blocks
(b) Machine Vises.
(c) Milling Fixture
(d) Dividing Heads
The Cutter Holding Devices
1. Arbors.
2. Adaptors
3. Collets
The Two Types Of Arbor
(i)
(ii)
Standard Arbor.
Stub Arbor.
Various Types Of Milling Attachments.
(i)
(ii)
(iii)
(iv)
(v)
(Vi)
(Vii)
Vertical Milling Attachment
Universal Milling Attachment
High Speed Milling Attachment
Rotary Attachment
Slotting Attachment
Rack Milling Attachment
Universal Spiral Milling Attachment
Milling Cutters.
According To The Shape Of The Tooth, Milling Cutters Are Classified As
(i)
Milled Tooth Cutters
(ii)
Form Relieved Cutters
According To The Types Of Operation.
(i)
(ii)
(iii)
(iv)
Plain Milling Cutters
Side Milling Cutters
End Mill Cutters
Angle Milling Cutters
73
(v)
(vi)
(vii)
(viii)
(ix)
T-Slot Milling Cutters
Slitting Saws
Form Milling Cutters
Flu Cutters
Wood Ruff Key Slot Milling Cutter
According To The Way Of Mounting On The Machine
(i)
(ii)
(iii)
Arbor Cutters
Shank Cutters
Face Cutters
Ten Nomenclature Of Plain Milling Cutter.
Body Of Cutter, Cutting Edge, Face, Filter, Gash, Lead, Land, Outside
Diameter. Roof Diameter, Cutter Angles.
The Two Main Group Of Milling Processes
i.
ii.
End Milling
Face Milling
Peripheral Milling Processes.
i.
ii.
Up Milling Or Conventional Milling And
Down Milling Or Climb Milling
The Rotation Of Cutter With Respect To Workplace Movement In Up Milling
The Cutter Rotates Opposite To The Direction Of Feed Of The Work Piece
The Advantages Of Up Milling Process
1. Safer Operation Due To Separating Forces Between Cutter And Work
2. Less Wear On Feed Screw And Nut Due To The Absence Of Pre-Loaded
74
3. Milled Surface Does Not Have Built Up Edge
Climb Milling Differs From Conventional Milling
The Cutter Rotates In The Same Direction Of Travel Of The Work Piece
The Advantages Of Down Milling Process
(i)
(ii)
(iii)
Cutter With Higher Take Angles Can Be Used. This Reduces Power
Requirements.
Cutter Wear Is Less Because Chip Thickness Is Maximum At The Start
Of The Cut.
Finishing Is Generally Good Because The Rubbing Action With Chip Is
Eliminated.
The Differences Between Up Milling And Down Milling
Sl.No
`Event Of
Operation
Direction Of
Travel
(I)
(II)
Chip Thickness
(Iii)
Cutting Force
Up Milling
Down Milling
Cutter Rotates Against The
Direction Of Travel Of Work
Piece
Minimum At The Beginning
Max When The Cut
Terminates
Increases From Zero To Max
Per Tooth
Cutter Rotates In The Same
Direction Of Travel Of
Workpiece.
Maximum At The Beginning
Greeches Min At Terminates
Decreases From Max To Zero
Per Tooth
Face Milling”.
Face Milling Is The Operation Performed By A Milling Cutter To Produce
Flat-Machined Surfaces Perpendicular To The Axis Of Rotation.
The Various Milling Operations.
1.
2.
3.
4.
Plain Or Slab Milling.
Face Milling
Angular Milling
Straddle Milling
75
5.
6.
7.
8.
9.
Gang Milling
Form Milling.
End Milling.
T-Slot Milling.
Gear Cutting.
Plain Or Slab Milling
Plain Or Slab Milling Is The Operation Of Producing Flat Horizontal Surface
Parallel To The Axis Of The Cutter Using A Plain Or Slab Milling Cutter.
The Following Terms: Straddle Milling And Gang Milling.
Straddle Milling Operation Is The Production Of Two Vertical Flat Surfaces On
The Both Sides Of The Job By Using Two Side Milling Cutters Which Are Separated
By Collars.
Term Indexing
Indexing Is The Process Of Diving The Periphery Of A Job Into Equal Number Of
Divisions.
Three Types Dividing Heads
1. Plain Or Simple Dividing Head.
2. Universal Dividing Head.
3. Optical Dividing Head.
Two Stage In Differential Indexing
Stage 1: The Crank Is Moved In A Certain Direction.
Stage 2: Movement Is Added Or Subtracted By Moving The Plate By Means
Of A Gear Train.
The Rule For Gear Ratio In Differential Indexing,
Rule For Gear Ratio In Differential Indexing:
( A  N )  40
Gear Ratio=
A
76
A Selected No Which Can Be Indexed By Plain Indexing And
Approximately Equal To N.
N Required No Of Divisions To Be Indexed.
Sl.No
(I)
(II)
(Iii)
`Event Of
Up Milling
Operation
Direction
Of Cutter Rotates Against The
Travel
Direction Of Travel Of Work
Piece
Chip Thickness
Minimum At The Beginning
Max
When
The
Cut
Terminates
Cutting Force
Increases From Zero To Max
Per Tooth
Down Milling
Cutter Rotates In The Same
Direction
Of
Travel
Of
Workpiece.
Maximum At The Beginning
Greeches Min At Terminates
Decreases From Max To Zero
Per Tooth
“Face Milling”.
Face Milling Is The Operation Performed By A Milling Cutter To Produce
Flat-Machined Surfaces Perpendicular To The Axis Of Rotation.
The Various Milling Operations.
1.
2.
3.
4.
5.
6.
7.
8.
9.
Plain Or Slab Milling.
Face Milling
Angular Milling
Straddle Milling
Gang Milling
Form Milling.
End Milling.
T-Slot Milling.
Gear Cutting.
Plain Or Slab Milling
Plain Or Slab Milling Is The Operation Of Producing Flat Horizontal Surface
Parallel To The Axis Of The Cutter Using A Plain Or Slab Milling Cutter.
77
Straddle Milling And Gang Milling.
Straddle Milling Operation Is The Production Of Two Vertical Flat Surfaces
On The Both Sides Of The Job By Using Two Side Milling Cutters Which Are
Separated By Collars.
Term Indexing
Indexing Is The Process Of Diving The Periphery Of A Job Into Equal Number
Of Divisions.
Three Types Dividing Heads
1. Plain Or Simple Dividing Head.
2. Universal Dividing Head.
3. Optical Dividing Head.
Two Stage In Differential Indexing
Stage 1: The Crank Is Moved In A Certain Direction.
Stage 2: Movement Is Added Or Subtracted By Moving The Plate By Means Of A
Gear Train.
The Rule For Gear Ratio In Differential Indexing, (Anna Uni Nov ’03)
Rule For Gear Ratio In Differential Indexing:
( A  N )  40
Gear Ratio=
A
A Selected No Which Can Be Indexed By Plain Indexing And
Approximately Equal To N.
N Required No Of Divisions To Be Indexed.
The Combination Of Two Movements Takes Place In Differential Indexing
When The Index Plate Rotates In The Same Direction Of The Crack The
Resulting Movement Of The Crank Will Increase. When The Index Plate Rotates In
The Opposite Direction Of The Crank, The Resulting Actual Movement Is
Decreased.
78
Drilling
Drilling Is The Process Of Producing Hole On The Work Piece By Using A
Rotating Cutter Called Drill.
Drilling Machines.
The Drilling Machines Are Classified As Follows:
1. Portable Drilling Machine.
2. Sensitive Drilling Machine.
a) Bench Type
b) Floor Type
3. Upright Drilling Machines
a. Round Column Type Or Square Section Type.
b. Box Column Type Or Pillar Type
4.
a.
b.
c.
Radial Drilling Machine
Plain Type
Semi-Universal Type
Universal Type
5.
6.
7.
8.
Gang Drilling Machine
Multiple Spindle Drilling Machine
Automatic Drilling Machine
Deep Hole Drilling Machine
The Various Parts Of Sensitive Drilling Machines.
A. Column
B. Table
C. Spindle And Driving Mechanism
Drilling Machine Is A ________
Higher Capacity Version Of Sensitive Drilling Machine.
The Various Parts Of A Upright Drilling Machine.
79
a.
b.
c.
d.
Base
Column
Table And Spindle Head
Driving Mechanism
The Main Components Of A Radial Drilling Machine
A. Base
B Column
C. Radial Arm
D. Drill Head
E. Spindle Head And Feed Mechanism
The Various Types Of Drilling Machines
A. Plain Type
B. Semi-Universal
C. Universal Type
The Main Use Of Multi-Spindle Drilling Machine
This Machine Is Suitable For Mass Production. In This Machine Several Holes
Of Different Sizes Can Be Drilled Simultaneously.
Gang-Drilling Machine
When A Number Of Single Spindles With Essential Speed And Feed Are
Mounted Side By Side On One Base And Have Common Workable, It Is Known As
The Gang-Drilling Machine.
Radial Drilling Machine
A Drilling Machine Is Specified By The Following Items.
1. Maximum Size Of The Drill In Mm That The Machine Can Operate.
2. Table Size Of Maximum Dimensions Of A Job Can Mount On A Table In Square
Meter.
3. Maximum Spindle Travel In Mm.
80
4. Number Of Spindle Speed And Range Of Spindle Speeds In R.P.M.
Four Operations That Can Be Performed In A Drilling Machine.
1. Drilling
2. Counter Sinking
3. Tapping
4. Trepanning
“Sensitive Hand Feed”
In Drilling Machine, Manual Sensing Of The Hand Does Feeding Of The Tool
Towards The Work Piece. It Is Called Sensitive Hand Feed.
Calculate The Tap Drill Size To Cut An Internal Thread For Bolt Of Outside
Diameter 10mm, And Depth Of The Thread 0.61 Pitch
Drill Size = Tap Size – 2 X Depth Of Threads
Depth Of Threads = 0.61 X 1.5 = 0.915mm
So Drill Size = 10-2 X 0.915 = 8.17mm
Reaming
Reaming Is The Process Of Sizing And Finishing The Already Drilled Hole.
The Tool Used For Reaming Is Known As Reamer.
1. Boring
4. Undercutting And
2. Counter Boring
5. Honing
Drilling Tool
1. Body 2.Shank 3.Neck 4. Point 5. Land Or Margin
Different Ways To Mount The Drilling Tool
1. Fitting Directly In The Spindle.
2. By Using A Sleeve
81
3.Spot Facing
3. By Using A Socket
4. By Means Of Chucks
The Reamer Tool Differs From Drilling Tool
A Reamer Is A Multi-Tooth Cutter Which Rotates And Moves Linearly In To
An Already Existing Hole.
The Use Of A Tapping Tool
A Tap Is A Tool Which Used For Making Internal Threads In A Machine
Component.
The Power Is Calculated In Drilling Operations
When A Drill Cuts It Should Overcome The Resistance Offered By The Metal
And A Twisting Effort Is Necessary To Turn It. The Effort Is Called Torque On The
Drill. The Torque Is Depending Upon The Various Factors. The Relation Between
Torques Diameter Of Drill And Feed Is As Follows.
T = C X F0.75 X D18
Where, T = Torque In N-M
F = Feed In Mm/Rev
D = Diameter Of Drill
C = Constant Depending Upon The Material Being
2 NT
watts
Power, P = 60
Where, N – Speed Of Drill In R.P.M.
Boring
Boring Is The Process Of Enlarging And Locating Previously Drilled Holes
With La Single Point Cutting Tool.
The Applications Of Boring
The Boring Machine Is Designed For Machining Large And Heavy Work Piece
In Mass Production Work Of Engine Frame, Cylinder Machine Housing Etc.
82
The Main Difference Between Boring Bar And Boring Tool
Boring Bar: The Tool Which Is Having Single Point Cutting Edge Known As Boring
Bar.
Boring Tool: The Tool Which Is Having Multi Point Cutting Edge Known As Boring
Tool.
The Types Of Boring Machines
The Boring Machines May Be Classified As Follows:
1. Horizontal Boring Machine
a. Table Type
b. Floor Type
c. Planner Type
d. Multiple Head Type
2. Vertical Boring Machine
3. Precision Boring Machine
4. Jig Boring Machine
The Work Is Clamped On The Table
The Work Piece Is Mounted On The Table And Clamped With Ordinary Strap
Clamps T-Slot Bolts And Nuts Or It Is Held In A Special Boring Fixture If So
Required.
MACHINING CALCULATIONS
1. Cutting Speed (V)
It Is The Velocity At Which The Metal Is Removed By The Tool.
83
Cutting speed , V 

Length of cutting stroke
Time taken for the same cutting stroke
LN (l  m)
1000
Where, L – Length Or Cutting Stroke In Mm
N – Speed In Rpm
M - Ratio Between Cutting Time And Return Time
2. Feed (F)
The Relative Movement Of Tool With Respect To The Work Piece Axis Is
Known As Feed.
Depth Of Cut (T)
Amount Of Metal Removed In One Revolution Or In Cut Is Known As Depth
Of Cut.
Machining Time (T)
Time Required For Machining The Work Surface To The Required Dimensions.
L
L
L L
T
  m  1  m 
NXf V
V V
Where,
L – Length Of Stroke = L+Approach + Over Run
N – Speed In Rpm
F – Feed
L – Work Piece Length
L/V – Time For Cutting Stroke
Ml/V – Time For Return Stroke
5. No. Of Strokes Required (SN)
The Ratio Between The Width Of The Work And Feed Per Stroke
84
SN 
W
f
6. Total Machining Time (T)
The Time Required For Machining The Entire Surface Of The Work As Per
Requirements.
7. Metal Removal Rate (W)
The Volume Of Metal Removed Per Unit Time.
Mmr (Or) W = Ftls
Where, F – Feed
T –Depth Of Cut
L – Length Of Work
S – Strokes Per Minute
8. Power Required
P=KXW
Where, K – Machining Constant.
9. Number Passes:
n
Stock to be removed S r

Depth of cut
t
SOLVED PROBLEMS
Problem 1
A Shaper Is Operated At 125 Cutting Strokes Per Minute And Is Used To
Machine A Work Piece Of 300 Mm In Length And 125 Mm In Width. Use A Feed
Of 0.6mm Per Stroke And A Depth Of Cut Of 6mm. Calculate The Total
Machining Time For Machining The Component. The Forward Stroke Is
85
Completed In 2300. Calculate The Percentage Of The Time When The Tool Is Not
Contacting The Work Piece.
Given Data:
S = 125 Strokes/Min
Work Piece Length, L = 300mm
W = 125 Mm
F = 0.6mm/Stroke
T =6mm
Forward Stroke Angle,  f  230o
Solution
Let Us Assume The Approach And Over Run = 25mm
Stroke Length L = L+25=300+25=325mm
W 125
SN  
 208.33  209
Number Of Strokes,
f
0.6

Total Time For Completing One Stroke,
L 325

S 125
 2.6 min .
T

Total Machining Time,
T1  TxS N  2.6 x 209
 543.4 min Ans.
Percentage Of Time When The Tool Is Not Contacting The Work Piece
360  0 360  230

x100
360
360
 36.11% Ans.
Angle of cutting stroke
m
Angle of return stroke

86
But, The Angle Of Return Stroke
 360   f 360 230130o
 Ratio, m 
230
 1.769 Ans.
130
Problem 2
Calculate The Power Required For Shaping Stect With A Depth Of Cut Of
2.8mm, Cutting Speed 65m/Min And The Work Length 50mm. The Feed Rate Is
0.5mm/Rev. Take Machining Constant K As 70x10—6.
Given Data:
T = 2.8mm
V = 65m/Min = 65x1000mm/Min
L =50mm
F = 0.5mm/Rev
Solution:
Material Removal Rate, W = F T V = 0.5x2.8 X
65 X 1000
P = Kw
Power Required, P = 79 X 10-6+ X 91000
= 70189 H.P Ans
= 7.189 X 0.736 = 5.29 Kw
Problem 3
Estimate The Shortest Machining Time Required In A Shaper To Machine A Plate
Of 200 X 90 Mm Under The Following Conditions.
Cutting Speed = 13.3m/Min
Feed = 0.57 Mm/Double Stroke
Number Of Passes = One
Approach + Overrun (Longitudinal) =20mm
(Lateral) = 4mm
87
Ratio Of Cutting Speed To Rapid Return = 0.83
Given Data:
Cutting Speed, V = 13.3m/Min
Feed, F = 0.5mm/Double Stroke
Number Of Pass, N=1
Approach Over Run, A = 20mm
Work Length, L = 200mm
Work Width W = 90mm
Ratio M = 0.83
Solution:
Length of cutting stroke
Time taken for the same stroke
Total / doublestroke  Time for forward stroke 
return stroke
Cutting speed V 
L
L
 m 
V
V 
L
 l  m
V
Total length, L  l  A  200  20
T 
= 220mm=0.22m
0.22
Total Time T =
1  0.83
13.3
 0.0303min
w
Number Of Strokes SN =
f
Total Width = W+ Lateral Approach
= 90+4 =94mm
94
 164.9  165 stroke,
SN = 0.57
Total time required for finishing the complete job
Tt  TxS N  0.0303x165
 4.9975mm  5min Ans.
88
Problem 4
The Cross-Feed On A Shaper Consists Of A Lead Screw Having 0.2 Threads
Per Mm. A Ratchet And Pawl On The End Of The Lead Screw Is Driven From
The Shaper Crank Such That The Pawl Indexes The Ratchet By One Tooth During
Each Return Stroke Of The Ram. Ratchet Has 20 Teeth.
a) Find The Cross Feed In Mm.
b) If A Plate 100 Mm Wide Has To Be Machined In 10 Minutes Find The
Cutting Speed In M/S. The Ratio Of Return To Cutting Speed Is 2:1 And
The Length Of The Stroke Is 150mm.
Given Data
Lead Screw Threads = 0.2 Thread/Mm
Ratchet Teeth
= 20
Plate Wide, W
= 100 Mm
Machining Time, T = 10min
Ratio Of Return To Cutting Speed 1/M = 2
Stroke Length L = 150mm
Solution
1
lead screw threads
1

 5mm
0.2
Pitch Of The Lead Screw =
1
revolution per each storke
20
a) Cross Feed:
F= Pawl Indexing X Lead Screw Pitch
Pawi Indexes

5
 0.25mm
20
Number Of Cutting Strokes,
w 100
SN = 
 400
f 0.25
Total Time Required To Complete The Job,
Tt = TXSN
89
= 10x400=400min
Cutting Speed, V =
Length of cutting stroke
L
Machining time, T 
Time taken for the cutting stroke
Nf
100
Nx0.25
N  0.1rpm
4000 
Cutting Speed,
V
LN (1  m) 150 x0.11  0.5 

1000
1000
 0.02225 m / min
Problem 5
A 75cm X 20 Cm Surface Of Cast Iron Block Of 15 Cm Thick Is To Be
Machined On A Shaper. Ram Speed Is 25mpm, Length Of Stroke Is 500 Mm,
Depth Of Cut Is 4mm, Feed Id 1.5mm/Stroke Stock To Be Removed Is 7mm Side
Cutting Edge Angle Of The Tool Is 450, Ratio Of Time Taken In Return Stroke To
The Time Taken In Cutting Stroke Is 0.5. Determine The Metal Removal Rate
And The Cutting Time.
Given Data:
Cast Iron Block Of 75 X 20 X 15 Cm
V = 25 Mpm
L = 500 Mm
T = 4mm
F = 1.5mm/Stroke
Stock To Be Removed = 6mm
  450
m  0.5
Solution
LN  l  m  500 x N 1  0.5 
V

1000
1000
N  33.33  34rpm
Metal Removal Rate W = F T L N = 1.5 X 4 X 500 X34
= 102 X 103 Mm3/Min
90
Number Of Passes N =
Stock to be removed
depth of cut
6
 1.5  2
4
LN 200 x 2

Nf 34 x1.5
 7.84 min Ans.
Total cutting time Tm 
Problem 6: Direct Or Rapid Indexing
Find Index Movement To Mill Hexagonal Bolt By Direct Indexing If The
Rapid Index Plate Has 24 Slots.
Solution:
Number Of Slots To Be Moved =
24 24

4
N
6
After Machining One Side Of The Bolt, Index Plate Has To Be Moved By 4
Slots For 5 Times To Finish The Work.
Problem 7: Compound Indexing
Compound Indexing For 87 Divisions.
Solution:
Required Movement Of The Work Piece =
40 40

N 87
Suppose We Select Two Circles Of 29 And 33 Holes. Substituting The Values
In The Expression 3.1. (Refer Compound Indexing)
87   33  29 
1

40  29  33
110
91
Since, The Numerator Is One, The Selected Circles Are Correct.
The Required Indexing Is Given By
40 110 110
11
23


3
3
87 33
29
33
29
23
11
or 3
3
29
33
Taking 3 As Common, The Above Expression Becomes
11 23
23 11

or

33 29
29 33
For Indexing, The Index Crank Should Be Moved By 23 Holes Of 29 Circle
Forward Directions And Then The Plate And The Crank Together Is Moved By 11
Holes Of 33 Circles In Backward Direction.
Problem: 8
Compound Index For 69 Divisions.
Solution:
Required Index Movement =
40 40

N 69
Suppose, We Select Two Circles Of 23 And 33 Holes. Substitute The Values In
Expression 8.1.
69  (33  23)
1

40  23  33
44
Since The Numerator Is Unity, The Circles Selected Are Correct.
92
The
Required Indexing Movement Is Given By
44 44 44
21
11


 1 1
69 23 33
23
33
Taking 1 As Common, The Above Expression Become
23 11

33 33
Thus For Indexing 69 Divisions, The Index Crank Should Be Move By 21
Holes Of 23 Hole Circle In Forward Direction He Then The Plate And The Crank
Together Is Moved By 11 Holes Of 33 Hole Circle In The Backward Direction.
Problem 9: Differential Indexing
Find Out The Indexing Movement Of Milling 119 Teeth Spur Gear On A
Gear Blank.
Solution:
Assume A = 120
A. Gear Ratio:
Gear on spindle stud
Gear on bevel gear shaft
40
 (A  N) 
A
40
 (120  119) 
120
=
40
 1
120
1 1 24 24
 

3 3  24 72
Gear ration =
A Simple Gear Train Is Used.
Gear On Spindle Will Have 24 Teeth.
Gear On Bevel Gear Shaft Will Have 72 Teeth
93
B. Index Crank Movement:
40 40 1


A 120 3
1 8
8


3  8 24

The Index Crank Will Have To Be Moved By 8 Holes In 24 Hole Circle For
Each Cut For 119 Times.
C Number Of Idlers:
As (A - N) Is Positive, A Simple Gear Train With One Idler Is Used. The
Index Plate Will Rotate In The Same Direction Of The Crank Movement.
Problem 10
Calculate The Spindle Speed To Drill A Hole Of 50mm Using Cutting
Speed As 25m/Min
Given Data:
Diameter Of Hole, D = 50mm
Cutting Speed, V = 25m/Min
Solution:
Cutting speed, V=
 DN
1000
  50  N
25=
1000
N = 159.15rpm say 160mm Ans.
94
Problem :11
Calculate The Feed In Mm/Rev To Drill A Hole Of 30mm In One Minute
To A Plate Thickness Of 40mm And Using A Spindle Speed Of 500rpm.
Given Data:
Diameter Of Hole, D = 30mm
Machining Time, T = 1 Minute
Thickness Of Plate, Tp = 40mm
Spindle Speed, N = 500rpm
Solution:
We Know That,
Machining Time, T =

Length of tool travel
Feed in mm / rev  r.p.m
t p  0.3D
Feed  N
40  0.3  30
I=
Feed  500
 Feed  0.098mm / rev Ans.
Problem 12
Calculate The Machining Time Required For Making 15 Holes On A M.S.
Plate Of 30mm Thickness With The Following Data:
Drill Diameter = 25 Mm
Cutting Speed = 20m/Min And
Feed = 0.13mm/Rev
Given Data :
Number Of Holes To Be Drilled = 15
Thickness Of The Plate, Tp = 30mm
Drill Diameter, D = 25 Mm
Cutting Speed, N = 20m/Min
Feed, F = 0.13mm/Rev
95
Solution:
We Know That
Cutting speed, V =
 DN
1000
  25  N
20 =
1000
N = 254.65rpm say 260 rpm
Length of tool travel
Machining time, t =
Feed in mm / rev  r.p.m.
t  0.3D
30  0.3  25
t p

Feed  N
0.13  260
t  6.66 minute for one hole
Total Machining Time, Tm = 6.66 X 15 = 9.99 Minute Ans.
Problem 13
A 40 Mm HSS Drill Is Used To Drill A Hole In A Cast Iron Black Of 80mm
Thick. Determine The Time Required To Drill The Hole If Feed Is 0.2mm/Rev.
Assume An Over Travel Of Drill As 5 Mm. The Cutting Sped Is 22m/Min.
Given Data:
Drill Diameter, D = 40mm
Thickness Of C.I.Block = 80
Feed, F =0.2mm/Rev
Over Travel, S = 5 Mm
Cutting Speed, V = 22m/Min
Solution:
We Know That
96
Cutting speed, V=
 DN
1000
  40  N
22 
1000
N  175rpm
Length Of Travel Of Drill = Tp +0.3D +Over Travel
= 80 + 0.3 X 40 + 5
= 97mm
97
0.2  175
=2.77minutes Ans.
Machining time, t =
Problem :14
Calculate The Power Required To Drill 25mm Diameter Hole In
Aluminium Plate At A Feed Of 0.2mm/Rev And At A Drill Speed 400rpm.
Determine Also The Volume Of Metal Per Unit Minute.
Given Data:
Drill Diameter, D = 25
Material: Aluminium
Feed, F =0.2mm/Rev
Drill Speed, N = 400rpm
Solution:
We Know That
Torque T=C  f 0.75  D1.8
From Table 3.1 For Aluminium, C = 0.11
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 T=0.11  (0.2)0.75  (25)1.8
= 10.8 N-m
2 NT 2  400  10.8
Power. P=

60
60
P = 452.4W Ans.
Volume Of Metal Removal/Minute
= Area Of Hole X Feed X Speed
=

4
 (25)2  0.2  400
= 32.27 X 103mm3 Ans.
32.27  103
Energy Consumption =
452.4
= 86.8m3/Watt Minute Ans.
Compare Peripheral Milling And Face Milling (MU Oct 1996)
What Are The Three Milling Processes
The Three Milling Process Are Face Milling, Slab Milling And End Milling.
In Face Milling, The Cutter Axis And The Work Piece Axis Intersect And The
Cutting Teeth On The Periphery Does Not Do The Cutting.
In Slab Milling (Peripheral Milling) The Cutter Axis Do Not Intersect, It Has Teeth
On The Periphery Only Which Does The Cutting.
In End Milling, Both The Face And The Periphery Does The Cutting Which Can Be
Seen In The Figure. Thus End Milling May Be Said To Be A Combination Of
Peripheral As Well As Face Milling.
Draw A Sketch Showing The End Mill Terminology.
98
Sketch A Milling Cutter And Indicate Rake, Clearance And Lip Angle. (MKU Nov
1996)
Though In The University Question Only The Sketch Of A Cutter Tooth And Few
Parameters Are Asked. I Have Given A More Elaborate Figure Of The Entire Cutter
For Better Understanding.
Arbor- Shaft On Which The Milling Cutter Is Mounted And Driven.
Body- That Part Of The Cutter Left After Exclusion Of The Teeth And The Portions
To Which The Teeth Are Attached.
Clearance Angles- Angles Formed By Primary Or Secondary Clearance And The
Tangent To The Periphery Of The Cutter At The Cutting Edge. They Are Called The
Primary And Secondary Clearance Angle Respectively.
Cutting Edge- Edge Formed By The Intersection Of The Face And The Circular Land
Or The Surface Left By The Provision Of Primary Clearance.
Face- That Portion Of The Gash, Adjacent To The Cutting Edge On Which The Chip
Impinges As It Is Cut From The Work.
Fillet- Curved Surface At The Bottom Of Gas Which Joins The Face Of One Tooth To
The Back Of The Tooth Immediately Ahead.
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Gash- Chip Space Between The Back Of One Tooth And The Face Of The Next Tooth
And The Face Of The Next Tooth.
Land- That Part Of The Back Of Tooth Adjacent To The Cutting Edge. Which Is
Relieved To Avoid Interference Between The Surface Being Machined And The
Cutter.
Lead- Axial Advance Of The Helix Of The Cutting Edge In One Complete
Revolution Of The Cutter.
Lip Angel- Included Angle Between The Land And The Face Of The Tooth, Or
Alternatively The Angle Between The Tangent To The Back At The Cutters With
The Shank, Between The Body And The Shank.
Outside Diameter- Diameter Of The Circle Passing Through The Peripheral Cutting
Edge.
Rake Angle (Axial)- Angle Between The Line Of Peripheral Cutting Edge And The
Axis Of The Cutter When Looking Radically At The Point Of Intersection.
Rake Angle (Radial) - Angle, In Plane Perpendicular To The Axis, Between The Face
Of The Tooth And A Radial Line Passing Through The Cutter Edge.
Relief Angle – Angle In A Plane Perpendicular To The Axis, Between The Relieved
Land Of A Tooth And The Tangent To The Outside Diameter Of Cutter At The
Cutting Edge Of That Tooth.
Root Diameter – Diameter Of The Circle Passing Through The Bottom Of The Fillet.
]
Shank - Plain Parallel Or Tapered Extension Along The Axis Of The Cutter
Employed For Holding And Driving.
Circumferential Form Relief – Clearance Produced On The Teeth By Reducing The
Diameter Of The Entire Form From The Cutting Edge To The Heel Via Curve- Linear
Fashion.
100
Circular Pitch- The Circular Distance Between The Adjacent Teeth Measured At The
Periphery Of The Cutter.
Depth Of Form – The Depth Of Form Is The Difference Between The Radial Distance
To The First And The Last Points Of The Cutting Edge.
101
UNIT – IV
UNCONVENTIONAL MACHINING PROCESS
PART – A
Abrasive
It Is The Material Of The Grinding Wheel Which Does The Cutting Action.
Dressing.
The Process Of Removing The Leading And Breaking Away The Glazed
Surface So That Fresh Sharp Abrasive Particles Are Again Presented To The Work
For Efficient Cutting Is Called Dressing.
Truing
Truing Is The Process Of Changing The Shape Of The Grinding Wheel As It
Becomes Worn From An Original Shape, Owing To The Breathing Away Of The
Abrasive And Bond.
Counter Sinking.
It Is The Operation Of Making A Cone Shaped Enlargement Or Recess At The
End Of A Hole. The Troll Used Is Called Counter Sink.
Trepanning
It Is An Operation Which Is Done When A Large Hole Is To Be Made In Thin
Metal Or When A Very Deep And Large Hole Is To Be Made In A Solid Work Piece.
Reaming
Reaming Is The Operation Of Finishing A Hole Very Smoothly And
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Accurately In Size.
Grinding.
Grinding Is A Process Of Removing Material By The Abrasive Action Of
Revolving Wheel On Surface Of A Work Piece In Order To Bring The Required
Shape And Size.
The Standard Marking Systems For Grinding Wheel
Types Of Abrasives




Grain Size
Grade Of The Wheel
Structure
Types Of Bond
Different Surface Finishing Processes.
Introduction
In A Manufacturing Plant, A Product May Be Shaped, Turned, Milled Or
Drilled, And Left In Condition As Being Satisfactory For Use. However, If A Better
Finish Is Desired, For Looks, For Accuracy, For Wearing Qualities, One Of The
Micro-Finishes That Include Lapping, Honing, Super Finishing Buffing, Burnishing
And Polishing May Be Employed. These Methods Remove Very Small Amount Of
Metal And The Surface Finish Is Specified In Micro-Inches And Hence The Name
Micro Finishes.
Lapping
It Is An Abrading Process For Refining Surface Finish And The Geometrical
Accuracy Of Flat, Cylindrical And Spherical Surfaces. It Is A Process Of Removing
Surface Roughness, Tool Marks, Surface Cracks From Grinding, Slight Distortions
And Other Minor-Defects From Previous Operations. It Is A Process To Improve
Surface Quality, Geometrical Precision And Dimensional Accuracy And To Provide
A Close Fit Between Mating Parts. Its Purpose Is Not To Remove Metal But To
103
Finish To Some Size. Lapping Consists Of The Use Of Loose-Grain Abrasive Sours
Mixed With Oil.
Abrasive Powders (Flours) Such As Emery, Corundum, Iron-Oxide,
Chromium Oxide, Etc., Mixed With Oil Or Special Pastes With Some Carrier Are
Used In Lapping. Most Lapping Is Done By Means Of Lapping Shoes Or Quills
Called Laps, That Are Rubbed Against The Work. The Face Of A Lap Becomes
“Charged” With Abrasive Particles. Charging A Lap Means To Embed The Abrasive
Grains Into Its Surface. Laps May Be Made Of Almost Any Material Soft Enough To
Receive And Retain The Abrasive Grains. They Are Made Of Soft Cast Iron, Brass,
Copper, Lead Or Soft Steel. The Method Of Charging A Lap Depends Upon The
Shape Of The Lap. When The Lap Is Once Charged, It Should Be Used Without
Applying More Abrasive Until It Ceases To Cut. Laps May Be Operated By Hand
Or Machine, The Motion Being Rotary Or Reciprocating The Lap Over The Work In
An Ever Changing Path. Small Flat Surfaces May Be Lapped By Holding The Work
Against A Rotating Disc., Or The Work May Be Removed By Hand In An Irregular
Path Over A Stationary Faceplate Lap.
Advantages Of Lapping:
1. Increases Work Life By Removing Surface Roughness And Irregularities.
2. Provides Superfine Surface Finish, Greater Uniformity And Optical Flatness.
Commercial Lapping Operations Can Produce Parts Accurate Upto Limits Of
0.0006 Mm.
3. Provides Liquid And Gas Tight Seals Without Using Gaskets Between
Plunger And Piston Without Rings.
4. Removes Errors In Gears Which Produce Noise And Undue Water.
Honing
Honing Is A Grinding Or A Abrading Process Mostly For Finishing Round
Holes By Means Of Bonded Abrasive Stones, Called Hones. Honing Is Therefore A
Cutting Operation And Has Been Used To Remove As Much As 3 Mm Of Stock But
Is Normally Confined To Amounts Less Than 0.25mm. So Honing Is Primarily Used
To Correct Some Out Of Roundness, Taper, Tool Marks, And Axial Distortion.
Honing Stones Are Made From Common Abrasive And Bonding Materials, Often
Impregnated With Sulphur, Resin Or Wax To Improve Cutting Action And
104
Lengthen Tool Life. Materials Honed Range From Plastics, Silver, Aluminium,
Brass, And Cast Iron To Hard Steel And Cemented Carbides. This Method Is Mostly
Used For Finishing Automobile Crank Shaft Journals.
When Honing Is Done Manually, Tool Is Rotated, And The Work Piece Is
Passed Back And Forth Over Tool. For Precision Honing, The Work Is Usually Held
In A Fixture And The Honing Tool Is Given A Slow Reciprocating Motion As It
Rotates. Honing Stones May Be Loosely Held In Holders, Cemented Into Metal
Shells Which Are Clamped Into Holders, Cemented Directly In Holders, Or Cast
Spaced At Regular Intervals Around The Holders, While Others Are Interlocking So
That They Present A Continuous Surface To The Bore. A Typical Honing Tool Head
Is Shown In Figure.
Coolants Are Essential To The Operation Of This Process To Flush Away
Small Chips And Keep Temperatures Uniform. Sulphursed Base Oil Or Hard Oil
Mixed With Kerosene Is Used.
Honing Is Done On Lathe, Drill Press, And Portable Drills.
Figure: Honing Tool With Adapter
105
Sl.No Point Of Comparison
Honing
1.
Creating Dimensions Possible
2.
Motions
Two
3.
Employment
4.
5.
Operating Speed
Pressure On Work
6.
Length Of Stroke
SUPER FINISHING
Super Finishing
Not Possible
Many Paty Of An
Abrasive Grain Is
Never Repeated
Mostly For Internal Largely For One Side
Surface
Surface.
Higher
Lower.
Higher
Too Low. Even Very
Fine Delicate Parts Can
Be Super Finished.
Longer
Low 1.5 M To 6 M.
A Defect Free High Quality Surface Finish Is Achieved By Operation Termed
As ‘Super Finishing’. The Main Features Of The System Are:
Complete Absence Of Defects In Surface Layer.
A Very Thin Layer (5 To 20 Microns) Is Removed,
Method May Be Used For Internal And External Surfacing Of Parts Made Of
C.I., Steel, And Non-Ferrous Alloys.
A Fine Grit (Grain Size 400-600) Abrasive Strata Is Retained In A Suitable
Holder And Applied To The Work Piece With A Light Spring Pressure.
Low Work Rotational Speed (2 To 20 Mpm).
The Work Piece Is Reciprocated To Me Requirement Of The Shape Being
Surfaced.
Longitudinal Feed Ranges From 100 To 150 Micron Per Work Piece Per
Revolution.
Abrasive Stick Oscillates Rapidly In Short Strokes (2 To 5mm) With A
Frequency Of 500-1800 Strokes Per Minute.
Spring Holds The Stick Against Work With A Force Of 20 To 100 N.
Special Lubricant (Mixture Of Kero And Oil) Is Used To Get High Quality
Finish.
Special General Purpose Machine Tools Are Available For Super Finishing.
Ordinary Machines Like Lathes Are Also Sometimes Employed. Single
106
Purpose Machine Tools For Finishing Crankshaft Journal And Crankshaft Are
Also Sometimes Used.
It Would Be Noticed That In Many Respects ‘Honing’ And Super Finishing
Have Certain Common Features And Certain Differences. These Have Been
Brought Out Is Table.
Table: Honing And Super Finishing Relative Comparison
Figure: Shaft For Super Finishing
Polishing
It Is A Surface Finishing Operations Which Is Employed For Removing
Scratches, Tool Marks And Similar Other Irregularities From The Job Surfaces
Produced Through Other Operations, Like Machining, Casting Or Forging. The
Primary Object Of This Operation Is Only To Improve Surface Finish And It Is,
Therefore, Employed Only Where Dimensional Accuracy Is Not To Be Closely
Controlled.
This Operation Is Performed By Means Of Abrasive Coated Wheels Or Belts.
The Wheels Used Are Disc Shaped And Termed As Bobs And Mops. The Former Is
Made Of Leather, Felt Or Wood, To The Periphery Of Which Are Coated The
Abrasive Particles With The Help Of Glue. These Wheels Operate At A Speed Of
1200 To 1500 Meters Per Minute (Linear) And Are The First To Be Used In The
Operation. They Are Followed By The Other Type Of Wheels, Called Mops, Which
107
Normally Operate Between 1000 To 1500 Meters Per Minute. They Are Made Of
Cloth, Or Leather. Both Natural And Artificial Abrasive Grains Are Used For
Coating These Wheels, But In Either Case They Should Be Of A Very Fine Grit. This
Operation May Be Done By Hand Or Machines. In Some Cases, Where Only A Few
Pieces Are To Be Polished, The Polishing Wheel Can Be Attached To Me Spindle Of
A Pedestal Grinder In Place Of Toe Regular Grinding Wheel, And The Operation
Performed By Feeding The Work Against It By Hand. For Production Work,
Specially Designed Semi-Automatic And Automatic Polishing Machines Are
Available.
Buffing
It Is Also A Surface Finishing Operation Which Is Usually Performed After
Polishing To Provide A High Luster To The Polished Surface. Obviously, There Is
No Appreciable Amount Of Stock Removal From The Work Surface. Wheels Used
In Buffing Are Made Of Linen, Cotton Cloth, Wool Of Felt, Which Are Charged With
Loose Abrasive Grains Almost In The Same Way As A Lap. Buffing Belts Are Also
Made In The Same Way As Wheels. A Very Fine Abrasive Is Used For Being
Charges To These Wheels Or Belts. Charging Is Usually Done By Means Of Sticks
Made Of Abrasive And Wax. Frequent Recharging Is Normally Needed During The
Operation.
Buffing Compounds
Buffs Are Designed To Carry An Abrasive Compound That Is Either Sprayed
On In Liquid Form Or Is Automatically Applied In Stick Form. Liquid Applications
Generally Offer Better Control Of Delivery And, When Employed Properly,
Guarantee That An Acceptable Level Of Compound Is Maintained On The Buff
Wheel.
Typical Compounds Contain A Number Of Abrasives Such As Aluminum
Oxide, Calcined Alumina, Red Rouge Iron Oxides, Green Chrome Oxides, Tripoli
And Pumice. Compounds Are Formulated For A Specific Task; Some Are Designed
For Heavy Stock Removal And Others To Achieve More Reflective Surfaces.
Tumbling
Jobs Are Tumbled In A Rotating Barrel Containing Abrasive Particles, Saw
108
Dust, Stones And Sand Along With Water Or Some Chemicals. The Process Is Used
To Remove Burrs Or Scale From Castings, Forgings And Screws Etc.
Burnishing
It Is A Process Of Polishing Without The Use Of Abrasive Particles. Solid
Tungsten Carbide Rollers Are Pressed Against The Rotting Job And Thus A Fine
Finish Is Obtained By The Rubbing Action Of Rollers On The Work Piece Surface.
The Process Is Used For Finishing Bronze Sleeves, White Metal Hearings And
Railway Axis.
The Different Types Of Sawing Machines
TYPES OF SAWING MACHINE
1. Reciprocating Saw
(A) Horizontal Saw (B) Vertical Saw
2. Circular Saw
(A) Cold Saw
(C) Abrasive Disk
(B) Steel Friction Disk
3. Band Saw
(A) Contour Band Saw (B) Friction Blade.
RECIPROCATING SAW
The Reciprocating Saw Is Usually Called Power Hack Saw. This Machine
May Be Crank Driven Or Hydraulic Driven. The Blade Is Reciprocated On The
Work Piece. During The Cutting Stroke, The Blade Is Forced Into The Work. It Is
Lifted Up During Idle Strokes. A Line Diagram Of A Crank Driven Power Hack Saw
Is Shown In The Figure. A Motor Drives The Crank. The Crank Gives Reciprocating
Motion To The Frame. The Frame Slides In A Guide Way Of The Over Arm. The
Over Arm Is Hinged To The Machine.
The Frame Is Fitted With A Straight Blade. The Machine Has A Quick Action
Vice. It Can Be Adjusted At Weight Provided On The Frame. It Is Called The
109
Gravity Feed. During The Idle Stroke The Frame Is Lifted Up By The Crank
Mechanism. It Is To Make The Blade Clear Off The Work. A Whit Worth
Mechanism Is Provided For The Quick Return Of Blade. A Cam Fitted To The Main
Shaft Carries A Cut Off Switch. It Cuts Off The Motor At The End Of A Cut.
Coolant Provision Is Made For Efficient Operation And Longer Life Of The Blade.
Figure: Reciprocating Saw
CIRCULAR SAW
The Machines Using Circular Saw Are Commonly Called Cold Sawing
Machines.
Figure: Circular Cold Saw Machine
110
A Line Diagram Of Hydraulic Feed Circular Cold Saw Is Shown In The
Figure. The Box Shaped Base Of This Machine Houses The Various Mechanism
(Chip Remover, Hydraulic Mechanism And Coolant Pump Etc). The Blade Carriage
Moves To And To And Fro On The Horizontal Guide Ways. The Guide Ways Are
Provided Or, The Top Of The Base.
Vice Or Hydraulic Clamping Mechanism Is Provided To Clamp The Work In
Position. The Lifting And Advancing Work Is Also Done By Hydraulic Means. An
Electrical Motor Is Provided To Drive The Saw Blade Spindle Through ‘V’ Belt,
Worm And Worm Wheel And Speed Gear Box.
The Blade Carriage Feed Is Operated Hydraulically. The Machine Has A
Wide Range Of Cutting Speed, Ranging From 6 Mpm. The Saw Blades Are Made
Solid Or With Segmental, Teeth Or Inserted Teeth. The Blades Cut Very Rapidly
Because Of Large Diameter, But It Runs At Relatively Slow Speed. The Cut Is Made
Very Smooth And Accurate.
BAND SAW
Introduction
In Band Saw, The Metal Is Cut By A Band. The Band Is An Endless Blade.
Band Saw May Be Vertical Or Horizontal Type. In Vertical Type The Work Is
Supported On A Horizontal Table. The Saw Runs In Vertical Position. In Horizontal
Type, The Work Is Held In Vice, A Small Band Saw Operates Above The Work
Nearly In A Horizontal Position.
Vertical Band Saw
A Vertical Band Saw Is Shown In Figure. The Bed Is A Box Type Hollow
Casting. It Is Cast Integral With The Vertical Column. The Lower Wheel Is Fitted
Inside The Bed. The Table Has A Long Slot At Its Centre. The Saw Blade Passes
Through It.
The Box Type Vertical Column, Houses A Coolant Pump Vertical Column
And The Electric Motor. The Top Portion Of Column Is Extended Out. It Is Support
The Upper Wheel. It Is Also Fitted With A Cover To Open Or Close. The Upper
111
Wheel And The Lower Wheel Are Connected By Means Of The Endless Saw Blade.
The Centre Distance The Two Wheels Can Be Adjusted, By Raising Or Lowering The
Upper Wheel. It Is To Adjust The Tension In The Blade. The Blade Is Kept Straight
By Means Of Guide Wheels When It Penetrates Into Work.
Figure: Vertical Band Saw
Horizontal Band Saws
This Type Of Machine Is Also Known As A Cut-Off Band Saw Or Cut-Off
Band Machine. In General Appearance They Look Like A Power Hacksaw, But The
Cutting Mechanism Of These Saws Is Quite Different. The Frame Of These
Machines Carries Two Wheels, With Their Axes Horizontal, Which Are Connected
Together By Means Of An Endless Saw Band. A Tension Control Mechanisms
Always Maintains Proper Tension In The Blade, So That It Runs Continuously When
The Wheels Rotate. One Of The Wheels Is The Driving Wheel, Connected To The
Motor, While The Other Wheel (Driven Wheel) Acts As An Idler Wheel. There Are
Two Guides Provided On The Path Of The Band. These Guides Turns The Blade
Such That It Runs Vertical Between The Two Guides To Cut The Work Piece Vertical
Cutting Of The Work Piece Due To Turned-Band By Guides Is Quite Clearly Visible.
The Frame Of The Machine Is Normally Hinged So That It Can Be Swing In A
Vertical Place To Raise It After Cutting Or Lower It Before Starting Sawing. A
Hydraulic Or Pneumatic System Controls The Cutting Fluid Supply And Many
Other Mechanisms Of The Machine.
The Adjustable Supports And Guides Incorporated At The Cutting Area
112
Support The Band To Enable It To Bear The Applied Cutting Force And Turn It To
Become Vertical To Saw The Work Piece In A Vertical Plane, As Shown In The
Diagram. Cutting Takes Place Due 10 Continuous Feeding Of The Band Into The
Work, Since The Saw Band Continuous To Run In The Same Direction Always.
These Machines Always Operate At Higher Cutting Speeds Than Those Used For
Reciprocating Power Hacksaws. A Few Important Points To Be Borne In Mind
While Operating These Machines Are:






Band Tension Should Be Correctly Adjusted.
Wheel Guards Should Be Locked Before Starting Sawing.
Proper Saw Blade, Speed And Feed Should Be Used.
Proper Coolant, If Required, Should Be Used And In Abundance.
The Band Supports And Guides Should Be Adjusted As Close To The Work
Piece As Possible.
The Work Piece(S) Should Be Tightly Clamped.
Figure: Principle Of Operation Of A Horizontal Bandsaw Machine
FRICTION SAW
Friction Sawing Machine Has A Disk. The Disk Is Nothing But A Circular
Blade. It Has Almost No Teeth. When The Disk Is Rotating At A Speed (About 6000
Mpm To 800 Mpm) Heat Is Produced Due To Friction. It Quickly Melts The Work
Piece In Contact With The Disk. Now The Tensile Strength Of The Steel Is Lowered
As The Temperature Increases. The Heated Metal Is Finally Weakened And
Removed By The Disk. Friction Sawing Is A Fast Cutting Operations With Less
Accuracy. It Is Not Limited By The Hardness Of The Material. It Can Easily Cut
Stainless Steel And High Carbon Steel. Non Ferrous Metals Cannot Be Cut
113
Satisfactorily In The Saw.
ABRASIVE CUT-OFF MACHINE
This Machine Has A Box Type Base. The Top Of The Base Is Used As Table.
A Vise Is Fitted On The Top Of Table. There Is A Swing Type Frame. It Is Pivoted
To The Body Of The Machine. A Motor Is Fixed At The Hack End Of The Frame. An
Abrasive Circular Saw Is Fitted To The Front End Of The Frame. The Abrasive
Circular Saw Is Nothing But A Blade Of This Grinding Wheel. The Wheel Gets
Power From The Motor Through ‘V’ Belt. The Wheel Rotates At High Speed.
Abrasive Wheel Is Fed Through Work, By Pressing The Handle Manually.
Figure: Abrasive Cut Off Machine.
Different Gear Generation Processes.
GEAR GENERATION PROCESS
Introduction
In Cutting Gears By Using A Generating Type Of Machine, The Gear Teeth
Are Formed As A Result Of Certain Relative Motions Between Gear Blank And
Cutter, Instead Of Simply Reproducing The Shape Of A Formed Cutter. A
Generating Process Is Capable Of Enabling A Cutter Of Given Pitch To Cut Gears
114
Having Different Numbers Of Teeth To The Correct Shape.
Gear Shaping
Shaper Cutter Generating Process: This Process Is Based On The Fact That
Any Two Involutes Gears Of Same Pitch Will Mesh Together. In The Shaper Cutter
Generating Process, The Cutter Is Given A Reciprocating Motion, As In A Shaper. It
Will Be Capable Of Cutting A Gear Blank And Generates Gear Teeth. A Gear Shaper
Cutter Is Shown In The Figure (A).
Figure (A) Gear Shaper Cutter.
The Figure (B) Shows The Setup And Operation Of A Gear Shaper Cutter.
Figure (B) Set Up Of Shaper Cutter Gear Generating Process
In The Operation, Both The Cutter And The Flank Rotate At The Same Pitch
Line Velocity And In Addition, A Reciprocating Motion Is Given To The Cutter. The
115
Rotary Feed Mechanism Is So Arranged That The Cutter Can Be Automatically Fed
To The Desired Depth While Both Cutter And Work Are Rotating. The Cutter Feed
Takes Place At The End Of The Stroke At Which Time The Work Is Withdrawn From
The Cutter By Cam Action. The Usual Practice Is To Have The Cut To Take Place On
The Down Stroke. Although In Some Cases The Cutting Action Is Of Necessity On
The Up Stroke. The Cutter Gear Method Of Generating Gears Is Not Limited To
Involute Spur Gears, But Has Many Other Applications. By Using A Spiral Cutter
And Giving It A Twisting Motion On The Cutting Stroke Spiral (Or) Helical Gears
May Be Generated. Worm Threads May Be Cut In A Similar Fashion.
Applications: Gears Produced By Gears Shaper Find Application In
Automobiles, Machine Tools, Instruments, Machinery, Clock And Other Equipment.
Pinion Cutter Generating Process:
The Pinion Cutter Generating Process Illustrated In Figures (A) And (B) Is
Fundamentally Same As The Rack Cutter Process And Instead Of Using A Rack
Cotter It Uses A Pinion To Generate The Tooth Profile. The Cutting Cycle Is
Commenced After The Cutter Is Fed Rapidly Into The Gear Blank Equal To The
Depth Of Tooth Required. The Cutter Is Then Given Reciprocating Cutting Motion
Parallel To Its Axis Similar To The Rack Cutter And Blank Are Made To Rotate
Slowly About Their Axis At Speeds Which Are Equal At The Mating Pitch Surfaces.
The Rolling Movement Between The Shaping Machines May Be Reciprocated Either
In The Vertical Or In The Horizontal Axis. The Following Are The Advantages Of
Pinion Cutter Generating Process.
116
Figure: Pinion Cutter Generating Process
 A Single Cutter Can Be Used For Cutting All Spur Gears Of Identical Pitch As
That Of The Cutter.
 Internal Gears Can Be Generated By Pinion Cutter Generating Process.
 The Rate Of Production Of Gears Is Higher, Because The Cutting Is
Continuous.
 The Mechanism Of The Machine Is Simple Than Rack Cutter Process.
Gear Planning (Rack Cutter Generating Process)
The Rack Cutter Generating Process Is Also “Gear Shaping Process”. In This
Method, Illustrated In Figure The Generating Cutter Has The Form Of A Base Rack
For The Gear To Be Generated. The Cutting Action Is Similar To The Action Of
Shaping Machine. The Cutter Reciprocates Rapidly And Removes Metal Only
During The Cutting Stroke. The Blank Is Rotated Slowly But Uniformly About Its
Own Axis, And Between Each Cutting Stroke Of The Cutter, The Cutter Advances
Along Its Length At A Speed Equal To The Rolling Speed Of The Cutter, The Cutter
Advances Along Its Length At A Speed Equal To The Rolling Speed Of The Mating
Pitch Lines. When The Cutter And Blank Have Rolled A Distance Equal To One
Pitch Of The Blank, The Motion Of The Blank Is Arrested, The Cutter Is Withdrawn
From The Blank To Give Relief To The Cutting Edges And The Cutter Is Returned To
Its Starting Position. The Blank Is Next Indexed And The Next Cut Is Started
Following The Same Procedure. The Helical Gears Are Cut By Swiveling. The Cutter
Slide To The Required Helix Angle. The Cutter Now Reciprocates In A Path Set By
The Helix Angle While The Rotary Movement Of The Blanks Is Continued. The
Following Are The Advantages Of Rack Cutter Generating Process.
Figure: Rack Cutter Geno-Rating Process
117

A Single Cutter Of Any Give Pitch Can Cut Gears Of Any Number Of Teeth
Having The Same Pitch.
 The Tooth Profile Generated Is Most Accurate Than Any Other Method.
 The Rate Of Production Is Higher Than That Of The Formed Cutter Method.
Gear Hobbing
Hobbing Is A Process Of Generating A Gear By Means Of A Rotating Cutter
Called Hob. The Hob Has Helical Threads. Grooves Are Cut In The Threads
Parallel To The Axis. This Will Provide The Cutting Edges. Proper Rake And
Clearance Angles Are Ground On These Cutting Edges. The Rotating Hob Acts Like
A Continuously Moving Rack As It Cuts.
Figure: Gear Hobbing
The Gear Blank Is Mounted On A Vertical Arbor. The Hob Is Mounted In A
Rotating Arbor. The Hob Axis Is Tilted Through The Hob Lead Angle A So That Its
Teeth Are Parallel At The Axis Of The Gear Blank.
Then = (90 - 1)
Where 1 = Helix Angle Of The Hob Thread
The Hob Axis Is Inclined At  With The Horizontal As Shown In The Figure.
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Figure:
Note: (Hob Lead Angle - 90 - Hob Helix Angle)
The Hob Is Related At Suitable Cutting Speed. It Is Fed Across The Blank
Face. The Hob And Blank Are Made To Rotate In Correct Relationship To Each
Other I.E., They Rotate Like A Worm And Worm Gear In Mesh. For One Rotation
Of The Hob, The Blank Rotates By One Tooth, (In Case Of Single Start Hob). Figure.
For Cutting Helical Gears, The Axis Of The Hob Is Inclined To Horizontal By
A Where.
 =  + (90 - 1) (If The Helix Of The Hob And The Helix Of The Gear To Be
Cut Are Different (I.E.) One Is Right Handed And Another
Is Left Handed.)
 =  - (90 - 1) (If The Helix Of The Hob And The Helix Of The Gear To Be
Cut Are Both Right Handed Or Both Is Left Handed.)
Where,
 = Helix Angle Of The Helical Gear To Be Cut.
 = Helix Angle Of The Hob.
Application:
Hobbing Is Used For Generating Spur, Helical And Worm Gears.
Advantages


A Single Hob With The Given Module Can Be Used For Generating Gear
With Any Number Of Teeth Of The Same Module.
The Same Hob Can Be Used For Spur And Helical Gears.
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




Operations Is Continuous. So Very Fast Rate Of Production.
Perfect Tooth Shape Is Obtained.
Worm Gears Are Generated Only By Hobbing.
Process Is Automatic And So Less Skived Operator Is Sufficient.
Multiple Blanks Can Be Cut At A Time. Hence High Rate Of Production.
Limitations:
 Internal Gears Cannot Be Generated.
 Hobbing Cannot Be Used For Producing Gear Teeth Very Near To Shoulders.
Bevel Gear Generator
There Are Two Types Of Bevel Gear Generators. They Are;


Straight Bevel Gear Generator.
Spiral Bevel Gear Generator.
Straight Bevel Gear Generator
The Generating Process Is Similar To Rolling Of A Bevel Gear Blank Of An
Imaginary Crown Wheel. The Crown Wheel Is A Bevel Gear Having Pitch Cone
Angle Of 180 (See Figure). The Teeth Of The Crown Wheel Are Straight And
Radial. In Practice, Instead Of All Crown Wheel Only Two Teeth Are Used For
Generation Of A Bevel Gear From A Blank. Two Cutting Tools In The Form Of Two
Teeth Of A Crown Wheel Are Used. The Tools Have The Profile Of Teeth Being Cut.
The Two Tools Together Cut Only One Tooth Space At A Time.
Figure:
The Machine Is Shown In Figure. The Gear Blank Is Held In An Arbor. The
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Axis Of Blank Is Inclined At An Angle With The Horizontal. The Angle Is 90 - 1 2
Pitch Cone Angle). The Blank Is Given A Rolling Motion About Its Axis. Two
Straight Cutting Tools Are Held In Reciprocating Sides. These Tool Slides
Reciprocate Along The Guide Ways On The Face Of A Cradle. The Cradle Rolls In
Relation To The Gear Blank. The Two Cutting Tools Reciprocate Across The Face Of
The Gear Blank. They Take Series Of Cuts On The Blank. By The Rolling Action Of
The Blank And The Cradle, The Tools Generate The Required Teeth On The Blank.
The Process Of Bevel Gear Generation Is Shown In Figure.
Figure:
At The Tool Position 2, One Of The Tool Starts Cutting The Gear Blank. In
The Position 3 And 4, Both The Tools Take The Cut. Now One Complete Tooth
Space Is Generated. Now The Cradle And Gear Blank Roll In The Reverse Direction
(Position 5). The Tools Also Slide Upwards. At Position 6, The Tools Get Relieved
Of The Blank. The Blank Is Automatically Indexed For The Next Teeth. The Cycle Is
Repeated.
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Figure:
Application:
In This Method, The Straight Bevel Gears Are Generated In Large Numbers.
This Process Can Also Be Used For Finishing Bevel Gears.
Short Notes On
i)
Gear Burnishing
ii)
Gear Shaving
iii)
Gear Grinding
iv)
Gear Lapping.
Gear Burnishing
This Is A Method Of Finishing Of Gear Teeth Which Are Not Hardened. This
Is A Cold Working Process. This Method Is Used To Improve The Surface Finish Of
The Gear Teeth. This Also Increases The Hardness At The Teeth Surface. The
Principle Of Working Of A Burnishing Process Is Shown In Figure. In Burnishing,
The Gear To Be Finished (Called Work Gear) Is Rolled Between Three Burnishing
Gears. The Teeth Of Burnishing Gears Are Very Hard, Smooth And Accurate.
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Figure: Gear Burnishing
They Are Arranged At 120 Position Around The Work Gear. Power Drive Is
Given To One Of The Burnishing Gears. The Other Two Gears Idlers. Burnishing
Pressure Is Applied To The Idlers. The Gears Are Rotated In One Direction For Same
Period. Then They Are Rotated In The Reverse Direction For The Same Period.
The Pressure Is Applied By The Herder Burnishing Teeth On The Work Gear.
The Surface Hardness Of Teeth In The Work Gear Is Also Increased. The Teeth Are
Finished On Both The Faces Uniformly. This Is Obtained By The Rotation Of The
Gears In Both The Direction.
A Lubricant In Applied Between The Teeth To Get Smooth Surface Finish.
This Also Reduces Friction And Heat.
Gear Shaving
This Is The Most Common Method Of Gear Finishing. In This Method, A
Very Hard Gear Shaving Cutter Is Used To Remove Fine Chips From The Gear
Teeth. The Shaving Cutter May Be In The Form Of A Rack Or A Pinion. The Rotary
Method Using Pinion Cutter Is Used On All Types Of Gears. The Rotating Cutter
Will Have Helical Teeth Of About 15 Helix Angle. The Cutter Has A Number Of
Serrations On Its Periphery. These Act As Cutting Edges.
Gear Finishing For Hardened Gears
Gear Grinding
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Gear Grinding Is Used For Finishing Gears After Hardening. Gear Grinding
Is Done For,
 Increasing The Accuracy Of Gears.
 Improving The Surface Finish.
 Removing The Distortion Due To Heat Treatment.
There Are Two Method Of Gear Grinding. They Are,


Formed Wheel Grinding
Generation Gear Grinding
A) Formed Wheel Grinding:
Informed Wheel Grinding, The Grinding Wheel Is Dressed To The Form Of
Tooth Space Of The Gear (Involute Profile). The Grinding Wheel Is Moved Parallel
To The Work Gear Axis.
Figure: Formed Wheel Grinding
After Grinding One Tooth Space, The Work Gear Is Indexed To The Next
Tooth Space. About Three Passes Are Required To Finish The Tooth Space. Proper
Coolant Should Be Used While Finishing By Grinding.
B) Generation Gear Grinding
The Work Gear Is Rolled Along An Imaginary Rack. Rolling Is Done In Both
The Directions To Grind Both Sides Of The Tooth. The Grinding Wheel Reciprocates
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Along The Length Of The Tooth. The Grinding Wheel Is Dressed In The Form Of
Rack Teeth.
Figure: Generation Gear Grinding
The Work Gear Rotates About Its Axis. The Gear Is Also Given A Linear
Motion Along Its Axis. The Linear Motion And Rotary Motion Are Opposite To
Each Other. These Two Motions Together Give A Generating Motion.
Figure: Generation Gear Grinding
Bevel Gears Are Also Ground By End Type Grinding Wheel As Shown In
Figure.
Gear Lapping
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The Hardened Gears Are Finished Accurately By Lapping Process. Lapping
Removes Very Small Amount Of Metal (Not More Than 0.05 Mm).
A Lapping Arrangement Is Shown In Figure. The Work Gear Is Rolled
Between Three Lapping Gears. The Lapping Gears Are Made Of Cast Iron. The
Lapping Gears Are Arranged At 120 Position Around The Work Gear.
Figure: Gear Lapping
The Axis Of The Two Lapping Gears (2 And 3) Is Inclined At About 4 To The
Work Gear Axis. The Axis Of The Other Lapping Gear (1) Is Parallel To The Work
Gear Axis. The Drive Is Given Through This Gear. When Gears Rotate, A Lapping
Compound Is Applied Between Them. The Compound Is A Mixture Of A Very Fine
Abrasive Powder And Kerosene. The Lapping Process Improves The Tooth Contact
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UNIT – V
CNC MACHINE TOOLS AND PART PROGRAMMING
PART – A
The Components Of NC Machine Tool.





Machine Control Unit
NC Program
Servo Mechanism
Machine Tool.
Manual Control
NC Program
NC Program Is An Instruction Set In The Form Of Numerals, Alphabets And
Symbols.
Incremental System
In This System The Tool Position Or Locations Are Indicated With Reference
To A Previously Known Location.
The Advantages Of CNC.
 Editing The Tape
 Unit Conversion
 High Productivity
Manual Part Programming
In Manual Programming The Programming Instruction Are Laid Down On A
Manuscript. Manuscripts Come In Various Forms Depending On The Capability Of
The Machine Tool.
Some Motion Statements In APT.
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GOUP, GO DOWN, GOFWD, GOBACK, GORUT, GOLFT Are The Motion In
APT.
Tool Reference
It Is The Point Of Rotation Of The Tool Post. It Is Useful For Cutter Tool
Compensation, Tool Changing Etc.
Cutter Compensation
When Part Program Are Prepared For A Particular Cutter Diameter The
Variations Is The Actual Cutter Diameter If Any In Given As Cutter Compensation.
PART – B
The Procedure For Developing Manual Part Programming.
Procedure For Developing Manual Part Programme
The Part Programming Requires An NC Programmer To Consider Some
Fundamental Elements Before The Actual Programming Steps Of A Part Takes Place.
The Elements To Be Considered Are As Follows:





Type Of Dimensioning System
Axis Designation
NC Words
Standard G And Codes
Machine Tool Zero Point Setting.
Type Of Dimensioning
After Deciding What NC Machine Is Best Suitable And Available For The
Application, We Determine What Type Of Dimensioning System The Machine Uses
I.E., Whether An Absolute Or Incremental Dimensional System.
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Axis Designation:
Another Consideration Is Designation Of The Axes Of The Machine Tool. In
Most Cases The Programmer Already Knows This Fundamental Element When He
Selects The NC Machine Tool For His Job. The Most Important Factor In Axis
Designation Is The Location And Position Of The Spindle.
The Part Programmer Also Determines How Many Axes Are Available On
Machine Tool I.E., X, Y,Z, A, B, Or C And So On And Also Whether Machine Tool
Has A Continuous Path And Point To Point Control System.
NC Words
In Order To Understand The Language Of NC Information Processing The
Following Definition Should Be Understood:
A ‘Bit’ Is The Basic Unit Of Information Represented By Either The Absence
Or The Presence Of A Hole Punched On The Tape. Bit Is An Abbreviation Of
“Binary Digit”, Which Can Be ‘0’ Or ‘1’.
A Code Or Character Is The Series Of Combination Of ‘1’s And ‘0’s. It
Represents A Number Or An Alphabet Or Any Symbol. One Character Is Punched
In A Single Row On The Tape E.G. Number ‘9’ Is Represented By 1001. Certain
Codes Or Characters Known As “Redundant Codes” Are Necessary To Reduce The
Possibility Of Incorrect Reading Of Tape By The Tape Reader. It Is An Information
Contained In The Data Which Is Not Essential But Is Added To Increase Readability
(E.G. A Code Known As “End Of Block” Or Simply ‘EOB’ Used To Separate Each
Block Of Data Irrespective Of Its Length).
An NC Word Is A Unit Of Information, Such As A Dimension (E.G. X01000
Or Y10025) Or Feed Rate (E.G. F200) And So On.
A Block Is A Collection Of Complete Group Of NC Words Representing A
Single NC Instruction (E.G. N1 G01X100 Z100 F100). An End Of Block (EOB)
Symbol Is Used To Separate The Blocks And End Of Block (EOB) Is A Hole Punched
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In 8th Columns Of The Tape. Various NC Words That Are Mostly Used Are As
Follows:
NG  XYZab  FSTM  EOB 
1. Block Number/Sequence Number (N Words):
Each Block Of The Program Has A Sequence Number Which Is Used To
Identify The Sequence Of Data In It Which Is In Ascending Numerical Order. When
The Part Program Is Read From The Tape, Each Sequence Number Is Displayed On
The Panel Of NC Machine Tool, As Long As That Block Commands Are Performed.
This Enables The Operator To Know Which Sequence Of Block Is Being Performed
Practically By The Tool. It Consist Of Character ‘N’ Followed By A Three Digit
Number Raising From ‘0’ To ‘999’.
2. Preparatory Functions (G-Words :
The Preparatory Function Is Used To Initiate The Control Commands,
Typically Involving A Cutter Motion I.E. It Prepares The MCU To Be Ready To
Perform A Specific Operation And Interpret, The Data Which Follows The Way Of
This Function. It Is Represented By The Character ‘G’ Followed By Two Digit
Number I.E. ’00 To 99’. These Codes Are Explained And Listed Separately.
3. Dimension Words (X, Y & Z Words):
These Dimension Words Are Also Known As ‘Co-Ordinates. Which Gives
The Position Of The Tool Motion. These Words Can Be Of Two Types:
(A) Linear Dimension Words
 X, Y, Z For Primary Or Main Motion
 U, V, W For Secondary Motion Parallel To X, Y, Z Axes Respectively
 P, Q, R For Another Third Type Motion Parallel To X, Y, Z Axes Respectively
(B) Angular Dimension Words
 A, B, C, For Angular Motion Around X, Y, Z Axes Respectively.
 I, J, K In Case Of Thread Cutting Is For Position Of Arc Center, Thread Lead
Parallel To X, Y, Z Axes.
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These Words Are Represented By An Alphabet Representing The Axes
Followed By Five Or Six Digits Depending Upon The Input Resolution Given. The
Following Points May Be Noted While Calculating The Number:
 Decimal Point Should Not Be Allowed E.G. X = 5.325 Will Be Represented As
X5325 In A Five Digits System I.E. The Last Three Digits Are Used For The
Decimal Part Of The Number. Some Machine Allow Omission Of Leading
Zeros, Hence The Same Can Be Represented As X5325.
 It Absolute System, All Dimension Should Be Expressed In Mm.
 All Angular Dimensions Should Be Expressed As A Decimal Fraction Of A
Revolution.
 In Absolute System, All Dimensions Should Be Positive.
 In Incremental System The ‘+’, ‘-‘ Sign Represent The Direction Of Motion.
4. Feed Rate Word (F-Word):
It Is Used To Program The Proper Rate, To Be Given In Mm/Min Or Mm/Rev
As Determined By The Prior ‘G’ Code Selection G94 And G95 Respectively. This
Word Is Applicable To Straight Line Or Contouring Machines, Because In PTP
System A Constant Feed Rate Is Used In Moving From Point To Point.
It Is Represented By ‘F’ Followed By Three Digit Number E.G. F100
Represents A Feed Rate Of 100 Mm/Min.
5. Spindle Speed/Cutting Speed Word (S-Word):
It Specifies The Cutting Speed Of The Process Or The Rpm Of Spindle. It Is
Also Represented By ‘S’ Followed By The Three Digit Number. If The Speed Is
Given In Meter Per Min, Then The Speed Is Converted In Rpm Of Spindle (E.G: S900
Represent 900 Rpm Of Spindle).
6. Tool Selection Word (T-Word):
It Consists Of ‘T’ Followed By Maximum Five Digits In The Coded Number.
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Different Numbers Are Used For Each Cutting Tools. When The T Number Is Read
From The Tape, The Appropriate Tool Is Automatically Selected By ATC (Automatic
Tool Changer). Hence This Word Is Used Only For Machines With ATC Or
Programmable Tool Turret. E.G. T01, T02, T03……. Represents The Tool Selection
Word.
Also Sometimes T-Word Is Used For Representing Offset Number
Corresponding To X, Y, And Z Directions. With The Help Of Two Additional Digits,
Given After A Decimal Point.
7. Miscellaneous Word (M-Words):
It Consists Of Character M Followed By Two Digit Number Representing An
Auxillary Function Such As Turning ON/OFF Spindle, Coolant ON/OFF Or
Rewinding The Tape. These Functions Do Not Relate Two Dimensional Movement
Of The Machine.
8. End Of Block (EOB):
It Identifies The End Of Instruction Block.
The Constructional Detail Of CNC.
Constructional Details Of CNC
A CNC Should Be Of “Robust Construction With Minimum Friction And
Backlash Eliminated”. The Design Consideration Of CNC Involves Stress Upon Two
Areas:
Control System Design
Mechanical System Design.
Control System Design
NC Machine Tool In The Past Had Been Very Unreliable. From A User Point
Of View, It Was Very Difficult To Believe, That What Happed To A Machine, Which
Had Given A Very Good Service For Years And Finally Lost Its Hand Wheels After
Marrying To An NC Controller. Obviously, The Controller Unit Also Lacked The
Reliability And Also The Proper Coordination Between Different Circuitry Element
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Or Parts. The User Is Confused Whether Between Relays, Transistors Or IC’s What
Is Reliable. Hence, For The Selection Of Control System, There Are Four Main
Considerations:
1. Analog Versus Digital
There Are Very Few Systems Which Are Either Completely Analog Or
Completely Digital. The Feedback Provided In The System Is Generally Of Analog
Form And Converts The Data In Digital Form. Hence, Without Getting Into The
Arguments Of Usefulness Of Both Systems, Care Should Be Taken For Selecting The
Technology For Different Units Of Control Unit.
2. Punched Tape Vs. Mag Tape
It Is Not Feasible To Use A System With Magnetic Tape As The Input For
Systems Of Simple Nature Such As Point To Point Applications Or Straight Lines
Because Programming And Preparing Punched Tapes Is Cheap And Easy. Even
Modifications Can Be Done Easily By Cutting A Part Or Simply Closing Holes Etc.
Wherease, In Case Of Magnetic Tapes A Large Volume Of Data E.G. Complex
Contouring Parts Can Be Handled By It. Sometimes Magnetic Tapes Have More
Detailed Cutter Path Information And Hence Eliminate The Used Of An Interpolator
But Need An Extra Off-Line Computer For Calculation Purposes. So, The Choice
Between Punched Tape And Magnetic Tape Depends Upon The Requirement
Stability.
3. Open Loop Vs. Closed Loop Systems
As Already Explained Before, Open-Loop CNC System Have No Feedback
Whereas Closed Loop Systems Make Use Of Feedback Transducers.
Although Closed-Loop Systems Seem To Be More Precise As Compared To
Open Loop Systems, But They Are Comparatively More Expensive Than O.L.S.
Moreover, Use Of Very Sophisticated “Digital Pulse Hydraulic Motor” Has
Eliminated The Need Of Closed Loop Systems.
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4. Linear Vs. Rotary Transducers
The Difference Between The Two, Is That Linear Transducers Get Direct Drive
From Actual Slide Displacement, Whereas Rotary Transducers Have Indirect
Measurement By Attachment To The Ends Of Lead Screws And Hence Only
Simulates The Relative Movement Of Tool And Work Piece.
Although Linear Transducer Such As Ferranti Systems Have Found To Be
More Accurate And Widely Accepted, But Slowly The Rotary Transducers Such As
Synchro Are Also Getting Accepted.
To Each Of The Above Factors There Are Certain Framed Rules Which Are
Proven Ones. Hence, Until And Unless We Get A Feedback From Electronic
Advisors, We Should Only Follow The Manufacture Of Repute.
Mechanical System Design
It Was Also Felt At A Later Stage That The Designs Of Conventional
Machines Often:
 Lack The Stiffness, Which Is Very Necessary For CNC Machines.
 Have Backlash I.E. Clearances In Threads Of Leadscrews Etc. Which Are
Almost Eliminated In CNC.
 Have Characteristic Of ‘Stick-Slip’ Which Appear To Be Very Difficult To Be
Controlled By CNC.
 Have Machine Tool Resonance And Have Machine Tool Chatter Which Is
Taken Care Of By :Chatter Compensation” In CNC’s.
All Of The Above Undesirable Characteristics Are Exhibited To A Less Or More
Extent In All Of The CNC’s Due To The Economic Reasons. But A Careful
Investigation All The Basic Mechanical Parts, Their Driving Mechanisms And Their
Relative Motions Can Solve This Problem To A Greater Extent.
These Are Following Machine Elements Or Systems Which Are Considered
At The Time Of Designing Of CNC Machines:
Main Structure Of CNC Machine Tool.
Slide And Slide Ways.
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Main Structure Of CNC Machine Tool
The Main Structure Of CNC Machine Tool Comprises Of A Bed, A Column
Other Member, Such As Head Stock Of Lathe, Which Is Connected To The Bed.
The Basic Structure Of Machine Tool Transmits Cutting Force From WorkPiece To The Foundation. There Are Two Types Of Forces Which Act Upon:
 Static Forces
 Inertia Forces
The Static Forces Are Exerted Commonly By The Weight Of Machine Tool
Itself And Pressure Of The Cutting Tool On The Work Piece. However, Gertia
Forces Are Exerted By Rapid Acceleration And Deceleration. Both Of The Forces
Tend To Bending Or Deforming The Table And This Way Head To Errors To The
Tune Of 40  Mm. For A Manually Operated Machine Tool The Operator Can
Correct The Error But In CNC Machines Control Tape Cannot Take Into The Forces
Acting During The Machining Operation. The Bending And Deformation Can Also
Be Caused Due To The Heat Effect In The Machine. The Heat Effect Can Put Tool In
Out Of Alignment And Deform The Machine Bed And Table. The Other Cause For
The Deformation Of Vertical Columns May Be The Mounting Of Driving Motors
Directly On The Cutting Arm. The Various Steps Which Can Be Taken To Counter
Cause Are:
a) Providing A Correctly Design Mild Steel Structure Having Stiffness.
b) Use Of Ribs, Braces, Angle Plates To Increase The Stiffness Of Machine
Structure.
c) Normal Weight Distribution Over The Entire Frame Of The Machine.
d) The Hollow Cross-Sections For Beds, Bases And Columns With A Number Of
Ribs Welded With The Walls Cater For The Rigidity As Well As Openings For
Inspection, Lubrication And Collection Of Chips Coolants.
e) Thermo Symmetrical Design Of All Parts.
f) Providing Large Heat Removing Surfaces.
g) Use Of Excellent Coolants.
h) Avoiding Direct As Well As Local Source Of Heat Such As Sun Light And
Electrical Motors/Oil Pumps Respectively.
i) Reduction Of Ambient Temperature By Using Air-Conditioning Units.
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j) Proper Alignment Of The Machine Elements Relative To Each Other While In
Operation As Well As In Stationary Conditions.
Figure: Thermal Sources Cause Of Inaccuracy In Machine Tools
Slide And Slideways
As We Know That The General Machine Tools Are Provided With Tables,
Slides, Carriages Etc. To Carry The Work Pieces Or Cutting Tools Etc. These Parts
Are Sliding Nature And Mounted On The Ways That Are Fixed On The Other Parts
(Column, Housing, Bed Or Knee) Of The Machines Known As Sliding Ways.
These Slideways Should Be Rigid, Accurately Designed And Durable.
As The Requirement For Accuracy And Location Of Tables/Saddles Increases,
More Attention Has To Be Given To The Frictional Resistance Of Slides. The SlipStick Motion Which Prevents Smooth Starting From The Rest Is Also Taken Care Of.
To Overcome This Drawback Antifriction Bearing Arrangements Are Done To
Substitute Sliding Friction With Rolling Friction. Different Methods To Achieve This
Phenomenon Are As
1. Hydrostatic Type Slideways
2. Anti Friction Type Slideways
3. Wear Resistant Slideways.
1. Hydrostatic Type Slideways
The Slideways Of Many Machines And Particular Those With A Horizontal
Bed Like Lathes, Exist Under Difficult Conditions For Cutting Forces Falling On The
Sliding Surfaces. It Will Lead To Increase Friction And Wear Along With Loss Of
Accuracy. Hence, A Constant Film Of Some Fluid Like Oil Or Air Prevents Metallic
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Contact Between The Sliding Members And Thus Reduces Wear To A Minimum.
Hydrostatic Slideways Can Be Sub-Classified As:
Oil Lubricated Slideways
Air Bearing Slideways
(I) Oil Lubricated Slideways: Stress Is Made On Maintaining An Unbroken Oil Film.
The Friction Is Minimizing By Forcing Oil Under Pressure Between The Mating
Surface And The Pressure Is Automatically Varied. According To The Load On The
Surface Resulting From The Weight Of Moving Member And Cutting Conditions.
These Types Of Slideways Are Best Suitable For CNC Milling Machines.
Figure: Hydrostationally Lubricated Slideways.
The Oil Lubricated Hydrostatic Slideways Is Shown In Fig.
2. Anti-Friction Type Slideways
Conventional Slides, Having Sliding Friction Have A Highest Value Of
Friction At Lowest Velocity. This Leads To A Jurky Action Due To Sticking Of Oil
Lubricated Sliding Surfaces. To Avoid This Situation A Point Or Line Contact Is
Made Instead Of Surface Between The Sliding Parts, There By Converting Sliding
Friction Into Rolling Friction.
3. Wear Resistant Slideways
The Machine Tools Vary In Ability To Resist Wear And Tear Of Their
Guideways. Machines, Such As Lathe And Planning Machine Operate Under Heavy
Loads Where As Grinding Machines Have Very Less Wear And Tear On Their
Slideways. For Economic Reasons, Cast Iron Is Used For The Body Of Both Types Of
137
Machines. Hence, A Different Type Of Bearing Surface Is Applied. Method Use For
This Purpose Is:
 Flame Hardening
 Induction Hardening
 Fastening Hardening Surfaces
 Surface Coatings
Spindle
It Is The Expensive And Live Part Of The Machine Tool Which Gets The
Power From Its Drive Unit And Delivers To The Work In Case Of Lathe Or To The
Tool In Case Of Drilling Or Milling Machine. In Case Of Lathe Machine, It Also
Holds The Work Piece. There Are Three Main Functions Of The Spindle As:
 Centering The Job Or The Tool
 Holding The Job Or The Tool
 Rotating The Job Or The Tool
So, On The Basis Of Above Functions, It Should Be Stiff And Short In Length
To Get Increased Stability And Minimization Of Torsional Strain. It Should Be Very
Close To The Front Bearing As Much As Possible To Maintain Stability And Smooth
Operation.
The Centering Of The Spindle Is Made By Providing Either Internal Or
External Tapers Or Cylinders. In Case Of Lathe Machine, The Spindle Consists Of A
Centre, Taper Bore, Adapters (To Suit Centres Of Different Sizes And Tapers) And
An External Cylinder To Locate Driving Chucks Plates As Shown In Fig. The Main
Spindle Is Supported On High Precision Taper Roller Bearings To Provide High
Rigidity, Thermal Stability And Consistent Production Accuracy.
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Figure: Lathe Spindle
In Case Of Milling Machine, The Spindle And Internal Taper, Locates The
Milling Heads Or Cutter Heads.
A Straight Fastening Passes Through The Full Lengths Of The Spindle As
Shown In Fig.
Figure: Milling Machine Spindle
The Tenons (Projections) Are Secured To The Spindle Nose By Means Of
Screws Which Transmits The Torque From The Spindle To The Arbor Or Milling
Head.
Advantages And Disadvantages Of Using NC System.
Advantages And Disadvantages Of Using NC Machines
Some Prominent Advantages And Disadvantages Using NC Machines Are
The Following:
Advantages:
1. Increased Productivity. Due To Reduced Setup And Lead Times.
2. Reduced Scrap. Due To Elimination Of Human Errors And High Accuracy Of
NC Systems.
3. Increased Rate Of Production. Due To Heavy Reduction In Non-Machine
Times And Optimization Of Machining Conditions.
4. Reduced Nonproductive Time. Due To The Use Of Lesser Setups, Lesser
Setting Time, Lesser Work Handling Time, Facility Of Automatic Tool
Changing On Some Machines, Etc.
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5. Reducing Lead Time For Manufacturing. Due To The Requirement Of Fewer
Setups And Less Setup Time.
6. Lesser Requirement Of Jigs And Fixtures. Due To The Fact That Work And
Tool Positioning Is Done By NC Tape, Only Simple And Cheaper Varieties Of
Fixtures May Be Needed In NC Machining.
7. Reducing Tooling Cost. Due To The Requirement Of Simpler And Less
Fixtures, The Cost Incurred On The Design And Fabrication Of Fixtures Is
Substantially Reduced.
8. Reducing Inspection Requirement. Due To The Production Of Parts Of
Uniform Quality.
9. Higher Accuracy. The Degree Of Accuracy Of Parts Producing Through NC
Machining Is So High And Quality So Uniform That There Is No Difficulty In
Interchangeable Use Of These Parts.
10. Better Quality Control. Due To Higher Accuracy Of NC Systems, The Quality
Of Products Is Effectively Controlled.
11. Ease Of Complex Machining. NC Facilitates Performing Of Complex
Machining Operations Easily, Accurately And At Much Faster Rate.
12. Greater Flexibility In Manufacturing. Due To Easy Adaptability Of NC To
Changes In Part Design, Changes In Production Schedule, Etc., According To
Requirements.
13. Reduce Inventory. The Firm Can Do With A Smaller Inventory Due To
Reduced Lead Times And Requirement Of Fewer Setups.
14. Greater Utilization Of Manpower. Since The Operator Is Not Required To
Attend To A Running NC Machine Constantly, He Can Be Utilized To
Perform Some Other Functions During That Period.
15. Reduction Of Human Error. Due To The Replacement Of All The Operator’s
Functions Of Conventional Machining By Tape In NC Machining, The
Chances Of Human Errors Are Reduced To A Minimum.
16. Enhanced Safety Of Operator. The Operator’s Involvement In NC Operations
Is Minimum Because The Console, Which Operates Different NC Systems, Is
Located At A Distance From The Machining Area, The Operator Gets No
Change To Be Exposed To This Area.
17. Better Safety Of Machine Tool. There Is Practically No Chance Of Any
Damage To The Machining Tool Due To Human Error Since There Is Almost
No Requirement Of Operator’s Involvement During The Operation.
18. Better Utilization Of Machine Tool. Due To Lesser Requirement Of Setup
Time And No Requirement For Operator Adjustments And Manipulations
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More Time Is Available For Machining, Leading To A Greater Use Of
Machining And, Thus, An Increased Rate Of Production.
19. Reduced Space Requirements. Lesser Storing Space Is Required In NC
Machining, Because A Few Jigs And Futures Are Needed. Also, When A NC
Machining Centre Is Used, It Eliminates The Requirement Of Many
Conventional Machining Tools, Which Results In A Reduced Space
Requirement For A NC Machining Shop.
20. Accurate Predictions. The Product Cost And Rate Of Production Can Be
Accurately Predicted Because Of The Programmed Machining, Which Does
Not Allow Any Deviation Of The Actual Production Time From The
Programmed Time.
21. No Need Of Skilled Operator. Since All The Manual Skills Required In
Conventional Machining Are Transferred To The Machine In NC, The
Essential Requirement Of A Skilled Operator Can Be Easily Done Away With.
Disadvantages:
1. Heavy Investment. Which Should Be Justified By Full Utilization Of NC
Machines, Otherwise The Invested Amount Will Be Blocked.
2. Costly And Complicated Maintenance. Because A Well Trained Maintenance
Task Force Is Needed.
3. Need Of Well Trained And Highly Skilled Manpower.
For Part
Programming.
4. Surplus Labour. This Happens If NC Is Made Applicable To Existing
Conventional Machine Tools. In That Case, A Fairly Large Workforce
Becomes Redundant And An Obvious Burden On The Organization.
5. Costly Control System.
The Different Components Of NC Machine Tool.
Components Of NC Machine Tool
The Main Components Of A NC Machine Tool Are:
1. Machine Control Unit
2. NC Program
3. Servo Mechanism And Drive Unit
4. Machine Tool
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5. Manual Control.
The Main Components Of The NC Machine Tool Are Shown In The Fig.
1. Machine Control Unit (MCU)
It Is Also Called As Controller Unit. This Consists Of The Hardware And
Electronics That Lead And Translate The Program Instructions Into Mechanical
Actions Of The Machine Tool. The Main Elements Of The Machine Control Unit
(MCU) Are A Tape Reader, A Data Storage Element (Data Buffer), Signal Output
Channels To The Machine Tool And Signal Feedback Channels From The, Machine
Tool.
Figure: Components Of Numerical Control
The Tape Reader Is An Electromechanical Device. The Purpose Of This Is To
Read The Punched Tape Containing The Program Instructions.
2. NC Program
NC Program Is An Instruction Set In The Form Of Numerals, Alphabets And
Symbols. These Instruction Sets Are Logically Organized To Carry Out A Set Of
Specific Machining Operation To Produce A Component Or “Part”. Hence It Is
Called As A “Part Program”. The Part Programs Are Coded (Written) By A Part
Programmer.
3. Servo Mechanism And Drive Unit
A Servo Mechanism Consists Of Elements Like Electric Motors, Gear Trains
And Lead Screws. It Converts The NC Input Into Precision Mechanical Movements
Of The Machine Tool Parts.
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4. Machine Tool
Machine Tool Converts The Work Piece (Blank) Into A Finished Product.
5. Operator Control/Manual Control
Figure: Configuration Of System-Computer Numerical Control
Operations Such As Motor Start-Stop, Change Of Speed, Change Of Feed,
Coolant Supply, Etc Can Be Performed Manually Using This Control.
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