MAHARASHTRA STATE BOARD OF TECHNICAL EDUCATION
(Autonomous)
(ISO/IEC - 27001 - 2005 Certified)
WINTER – 12 EXAMINATION
Subject Code : 12091
Model Answer
______________________________________________________________________________________________
Sub
Que. Qu.
Step by Solution/ Correct Answer etc.
No No.
Q. 1 (a) State the significance of ‘Rake angle’
Max. Marks
for Qu./
Sub Qu.
Ans The rake angle is the slope of the top away from the cutting edge.
Single point cutting tool has two rake angle namely side rake and back
rake angle. A large rake angle is desirable to good surface finish. Side
02 marks
rake angle reduces the cutting force required to shear the metal. It helps
to reduce the power consumption and increase tool life.
b)
Define the term ‘feed rate’
Ans The feed of a cutting tool is the distance the tool advances into or along
the work piece in one rotation. The tool point passes a certain positions
in its travel over the surface.
02 marks
In case of lathe operation the feed is the distance that the tool
advances in one revolution of the work piece. It is expressed in
mm/revolutions.
c)
How CNC machines are classified ?
a. Based on feedback control i) open loop system ii) Closed loop
system.
b. Based on control system features. I) Point to point control
02 marks
system ii) straight line control system iii) Continuous path or
contouring control system.
d)
What is meant by ‘Statement of CNC Programming’ ?
It is data in single block consisting of number of G & M Codes inserted
in one line which are actuated simultaneously. It is also called as block
02 marks
e.g. N10 G71 G 90 G94 EOB.
e)
State the functions of drilling machine. (any two , 1 mark for each)
i) To drill a hole in w/p.
ii) For tapping operations.
iii) For reaming operations.
iv) For treapening operations.
f)
Enlist the applications of “Deep hole Drilling machine. (any two , 1
mark for each)
When drilled hole length is generally more than five times its diameter
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______________________________________________________________________________________________
this drilling machine is known as deep hole drilling machine.
Following are few applications of deep hole drilling machine
i) Rifle barrels.
ii) Crank shafts.
iii) Long shafts.
iv) Hollow spindles.
v) Connecting rods. Etc
g)
State the use of mandrel in milling machine.
Basically the mandrel is used for holding hollow jobs. In case of milling
for cutting the teeth on gear blanks. The w/ps are mounted on mandrel
02 marks
on dividing head/dead center.
h)
What is meant by indexing ?
The indexing is the operation of dividing the periphery of a work piece
into any number of equal parts.
02 marks
Ex : i) cutting gear tooth on gear blank.
ii) Drilling nos. of hole in periphery.
i)
Enlist the various types of milling cutters.
Following are the different types of standard milling cutters.
1) Plain milling cutter a) light duty b) Heavy duty c) Helical plain
milling cutter.
2) Side milling cutter. a) Plain side milling cutter b) Staggered
teeth side milling cutter c) Half side milling cutter d) Inter
locking side milling cutter.
3) Metal slitting saw. a) Plain metal slitting saw b) staggered teeth
metal slitting saw.
4) Angle cutter. a) Single angle b) double angle.
5) End mill a) Taper shank end mill b) Straight shank end mill c)
shell end mill.
6) T-Slot milling cutter.
7) Woodruff key slot and fly cutter.
8) Formed cutter a) convex b) concave c) corner rounding d) gear
cutter e) Thread milling cutter.
9) Tap & reamer cutter.
As this bit is asked for 2 Marks any four cutter listed by students full
Page 2 of 18
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WINTER – 12 EXAMINATION
Subject Code : 12091
Model Answer
______________________________________________________________________________________________
marks may be given.
j)
State the advantages of Gear hobbing operation. (any two , 1 mark
for each)
i) This processes is continuous cutting hence the process is fast
and the rate of production is very high.
ii) It is also possible to generate internal gears.
iii) It is versatile process in that it can cover a variety of work
including spur gear, helical, worms and worm wheels,
splines and serration gears.
iv) The gear teeth generated by this process are very accurate.
v) Cost economical for batch or mass production
k)
What is the use of ‘Dividing Head’? (any two , 1 mark for each)
1) For setting the work in vertical, horizontal or in inclined
position.
2) For turning the W/P periodically through a given angle to impart
indexing.
3) For imparting continuous rotary motion to the W/P for milling
helical groves.
l)
Define term module.
It is the linear distance in mm that each tooth of the gear would occupy
02 marks
or It is ratio of pitch circle diameter to number of teeth in gear i.e.
m=D/T.
m)
What is grade of grinding wheel.
The term grade as applied to grinding wheel means. It is hardness of
the wheel with which the bond holds the cutting points/ abrasive grains
in a place. There are three types of grades of grinding wheel
02 marks
i)
soft ii) Medium iii) Hard. It is denoted by English letter A to Z.
n)
State the applications of honing operations. (any four , 1/2 mark for
each)
The main purpose of the honing is to remove the scratches on the
surface left by previous operations. It is used for engine cylinder, gun
barrels, and long tubular parts, bearing rings, gear teeth, valve seating,
races of ball/roller bearing, piston rod, spindles, shaft etc. This process
can be applicable for internal as well as external surface machining and
brought parts within accurate dimension or within tolerance.
Page 3 of 18
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WINTER – 12 EXAMINATION
Subject Code : 12091
Model Answer
______________________________________________________________________________________________
o)
What is Extrusion. ( diagram not essential)
The extrusion means continuous flow of material through a die. It is the
process of pushing the heated billet or slug of metal through an orifice
provided into a die, thus forming as elongated part of uniform cross
section. The pressure is applied either hydraulically or mechanically.
02 marks
Q. 2
a)
How taper turning operation is carried out on lathe machine ?
Explain with suitable example. ( 01 mark for names of methods &
03 marks for explanation )
Taper turning in performed by five different methods.
1) Taper turning by broad nose form tool.
2) Taper turning by swivelling the compound rest.
3) Taper turning by set over method.
4) Taper turning by attachment.
5) Taper turning by combining longitudinal and cross feed.

The job is clamped and rotated in three jaw check.

The tool is fed at an half angle to axis of rotation of work piece.

Angle of inclination calculated as Tan  
Dd
; is half
2L
angle to be set.
Where D - Larger diameter.
d - Smaller diameter
L- Entire length of taper.

The tool is mounted on compound rest is attached a circular
base, graduated in degrees.

Compound rest is swiveled and clamped to calculated angle.

The movement of the tool in this method being purely controlled
Page 4 of 18
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______________________________________________________________________________________________
by hand.
b)
What is ‘Tool Signature’ ? Explain with neat sketch for single point
cutting tool. ( 01 mark for defn. & 03 marks for fig. & explanation)
The tool signature means a sequence of numbers listing the various
angles in degrees and the size of nose radius. There are two systems to
designate the tool shape which are widely used
1) Machine reference system. It is also known as American
standard association system (ASA).
2) Tool reference system or orthogonal Rake system (ORS) The
seven parameters that used to designate a single point cutting
tool is stated in the following order.
8 – 14 – 6 – 6 – 6 – 15 – 4
It means that
c)
i)
8º - back rake angle.
ii)
14 º - Side rake angle.
iii)
6 º - end relief angle.
iv)
6 º - end/side relief angle.
v)
6 º - end cutting edge angle.
vi)
15 º - side cutting edge angle.
vii)
4mm – is nose radius.
State the advantage of CNC lathe machine over conventional lathe.
( Any four, one mark for each)
Following are the advantage of CNC lathe over conventional machines.
1) In case of CNC lathe the carbide tip tools are used hence cutting
speed faster than conventional lathe & also high feed rate.
2) CNC lathe movement is controlled by computer (which runs the
Page 5 of 18
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WINTER – 12 EXAMINATION
Subject Code : 12091
Model Answer
______________________________________________________________________________________________
programme while in conventional lathe manual or auto feed is
given. More flexibility available in CNC lathe.
3) CNC lathe can achieve higher accuracy with closed tolerance
and very good surface finish as compared to conventional lathe.
4) Once the programme is prepared and fed, less manual
interference required in case of CNC lathe hence less skill
operator can work on the machine.
5) Though the initial cost of CNC lathe is more but for mass
production and accuracy and quality job CNC lathe has very
good option than conventional lathe.
6) Programme can be stored in the memory and can be used when
ever required in batch production. Such facility is not available
in conventional lathe.
7) Machines are comparatively small, need not required rigid
foundations as conventional machines. Less vibration.
8) For superior repeatability, reduce machine down time as fast
machining cycle.
9) Tool path simulation are available in CNC lathe which gives
idea about job. This feature is not available in conventional
machine.
d)
Explain the nomenclature of twist drill. ( 02 marks for fig. & 02
marks for explanation of any two)
The nomenclature means the designation of the shape of the cutting part
of the drill. Following fig shows twist drill nomenclature.
The definition of imp. Drill elements may be given for explanations.
Page 6 of 18
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WINTER – 12 EXAMINATION
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Model Answer
______________________________________________________________________________________________
Neck : The diametrically undercut portion between the body & the
shank of the drill.
Flute : The groove in the body of the drill which provides lip.
Land : The cylindrically ground surface on the leading edge of the
drill flutes.
Heel: the edge formed by the intersection of the flute surface & the
body clearance.
Shank : The part of the drill by which it is held & driven .
Tang : The flattened end of the taper shank intended to fit into a
slot in the spindle, socket or drill holder.
Overall length: The length over the extreme ends of the point &
the shank of the drill.
Flute length : The axial length from the extreme end of the point to
the termination of the flute at the shank end of the body.
Lip angle : The angle formed by the flank & the plane at right
angles to the drill axis.
Helix angle: it is the angle formed by the leading edge of the land
with a plane having axis o the drill.
( any four of the above )
e)
What is slitting operation? State its applications.
( 02 marks for def. & 02 marks for applications, any two)
It is the operation to cut or parting of W/P using metal saw. It is a thin
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______________________________________________________________________________________________
plain metal cutter having teeth on its periphery only. The teeth are
ground to give clearance while cutting. The teeth are ground towards
centre so that the side of cutter will not rub in the grooves to be cut. It is
used for the cutting slots or for parting off operations.
There are two types of slitting cutters.
1) Plain metal slitting saw – These cutters are thinner in
construction and their width is limited to 5 mm. it has teeth of
constant thickness
2) Staggered teeth metal slitting saw : These cutters have staggered
teeth alternatively and also side teeth. Their width varies from 5
to 10 mm. They are used for comparately heavy work.
f)
Explain in brief ‘Gear sharing operation’
The shear speed process involves the production of all the teeth on a
gear simultaneously by a ring of formed blades arranged on the
periphery of the gear blank. Each blade having formed cutting edges
cuts one tooth space. And the number of blades on the cutter equals the
number of tooth spaces on the gear. The work piece is mounted on the
ram of a shear speed gear shaper and is reciprocated against the fixed
04 marks
blades of the cutter. There is an automatic arrangement for radial
adjustment of the blades so that the blades are retracted during the time
of return stroke to provide relief to the cutting edges. The depths of the
cuts are also adjusted by a radial movement of the blades. The shear
speed process is the quickest method of producing external and internal
spur gear splines, toothed clutches, ratchet wheels etc.
Q. 3
a)
Attempt any two ( 04 marks for explanation & 04 marks for any
suitable example)
Explain in detail “canned cycle with example.

It can be defined as set of instructions stored in the memory of
the system, to perform fixed sequence of operations.

It is called as fixed cycle.

It is used for repetitive operation where material is to cut in
multiple passes.

It reduces the length of program and its complexity.

It can be called in the program by using G-codes.
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WINTER – 12 EXAMINATION
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Model Answer
______________________________________________________________________________________________

Canned cycles should be cancelled after their use by using the
code G-80.

Canned cycle can be used for drilling, slot milling,

Example: To mill a slot of 10 mm deep in flat workpiece.
Tool Path
Format G74 Xf Yf Zf K ____ S _____ F _____ EOB
K = Peck depth
S = Peek feed
F = Feed.
b)
( 04 marks for facing opn. & 04 marks for turning opn.)
NO1 G90 G71 G94 EOB
NO2 G00 X0 ZO M03 S800 EOB
NO3 G01 X-13 EOB
NO4 G01 Z+1 EOB
NO5 G01 X+13 EOB
NO6 G01 Z-1 EOB
NO7 G01 X-13 EOB
NO8 G01 Z0
EOB
NO9 G01 X+13 EOB
N10 G01 Z-2 EOB
N11 G01 X-13 EOB
N12 G01 Z0 X 13
EOB
N13 G00 Z-2 X0 EOB
N14 G01 X-0.5 EOB
N15 G01 Z-62 EOB
N16 G00 X00 Z00 EOB
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Model Answer
______________________________________________________________________________________________
N17 G01 X-1.0 EOB
N18 G01 Z-62
EOB
N19 G00 X0 Z0 EOB
M02
EOB
c) i) Positioning system : (Point to point motion control system)

Point to point motion control system are those in which the
positioning the cutting tool at a predetermined locations relative
to W/P.

The machining operation is done only after the tool has taken
particular position w.r.t. position of W/P or vice versa.

The tool reaches a particular fixed point in the shortest time
span with shortest path.

Example

Drilling no. of holes on a flat plate (Rotary table rotates and
particular pt. is brought below to drill spindle)

Punching holes at different locations.

Spot welding at different spots.
04 marks
Jig boring at different reamed holes.
Retrofitting :
ii)
Retrofitting means, substitute new or modernized parts or equipments
for older lathe.
Providing with parts, devices, equipments which are not available or in
use at the time of original manufacturing. (02 marks)
Exp :

The car companies retrofitted all old models with new
carburetor.

The lead screw of lathe and screws of slides are replaced by
recirculating ball screw.

Display devices which shows the current positions of slides
during machining (02 marks for any two)
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Q. 4
a)
T-Slot milling. ( 02 marks for fig. & 02 marks for explanation)
i)

The ‘T’ slot is produced by first milling a plain slot on work
piece.

The shank of the ‘T’ slot milling cutter is introduced through the
first machined slot.

The second slot is cut at right angles to first slot by feeding w/p
past the cutter.
ii)
Face milling: ( 02 marks for fig. & 02 marks for explanation)
It is performed to produce flat surfaces perpendicular to the axis of
rotation of cutter.

Peripheral Edges actual cuts the material and face cutting edges
finishes the work surface

The thickness of chip is minimum at beginning and at end of
the cut, and max. when work passes through the centre line of
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cutter
b)
Gear hobbing techniques :
1) Climb hobbing
2) Conventional hobbing.
02 marks
( Sketch & explanation of any one method should be written.
03 marks each for sketch & explanation)
Conventional Hobbing :

In conventional hobbing, when the hob swivel setting angle is
small, the hob is fed along the workpiece in a direction which is
in agreement with the tangential vector denoting the direction of
hob rotation.

For components having larger helix angles, conventional type of
hobbing is employed.

The chips removed vary in size & shape.

Chip starts out thin & becomes increasingly thicker as the hob
06 Marks
tooth sweeps through the cut.
Climb hobbing

With small hob swivel setting angles, climb hobbing takes place
when the hob is fed into the workpiece in a direction which
opposes the tangential vector denoting the direction of hob
rotation.

Chip starts out thck & becomes increasingly thinner as the hob
tooth sweeps through the cut.

The choice of climb type cutting over the conventional type
cutting is based in comparison of surface finish obtained from
each.
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c)
State the principle of gear shaping operation what are the
adv. And limitations of gear shaping operation.
( 04 marks for principle & 02 marks each for adv. &
limitations)

In gear shaping operation, the cutter removes material by
reciprocation.

The gear cutter is very similar to the gear but the teeth are form
relieved to act as cutting edges.

The gear shaper cutter is mounted on vertical arm and is rotated
about its axis.

The relative rotary motion of the shaping cutter and gear blank
are calculated as per requirement.

The cutter slowly moves into gear blank surface with
incremental depth of cut till it reaches the full depth.

The cutter and gear blank are separated during the return stroke
and come to correct position during cutting stroke.
Advantages :
1.
Gear shaping can cut internal gears , splines &
continuous herringbone gears that can not be cut by
other processes.
2. This process can also cut gears close to a shoulder with
very small clearance.
3. Racks which can not be produced by hobbing can be
rapidly & accurately produced by shaping.
4. Since the approach & overtravel are small, this process is
fast for narrow gears.
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Limitations :
1. There is no cutting on return stroke . Hence about only
half the machine time is spent in metal removal.
2. Worm & worm wheels can not be easily generated on
gear shaper.
3. The production rate of gear shaper is lower compared to
gear hobbing.
Q.5
a) Explain in detail, how grinding wheels are designated with suitable example.
Example- 4 marks, Description- 4 marks (one mark for each characteristic)
The standard marking system (as per IS 551-1996) is arranged in the following sequence:
0- Manufacturer additional symbol for the abrasive(optional)
1- Type of abrasive
2- Grain size
3- Grade
4- Structure
5- Type of bond
6- Manufacturer own wheel identification
1) Abrasive Type-These are hard materials with adequate toughness which act as cutting edges
for a sufficiently long time. They have also the ability to fracture into smaller pieces when the
force increases.
Types of Abrasive
i) Natural Abrasive- corundum, emery and diamond are the most commonly used natural
abrasives.
ii) Manufactured or Artificial abrasives-silicon carbide, aluminium oxide and cubic boron nitride
are the commonly used manufactured abrasives.
2) Type of Bond- A bond is an adhesive substance that is used to keep the abrasive grains
together under the action of grinding force. The choice of the bond depends upon the accuracy,
the surface finish required and nature of grinding operation. Commonly used the bonding material
are:Vitrified bond, Silicate bond, Shellac bond, Resinoid bond, Rubber bond, Oxychloride bond,
metal bond.
3) Grade: - The grade is also called the hardness of the wheel. This designates the force holding
the grains. The grade of a wheel depends on the kind of bond, structure of wheel and amount of
abrasive grains. The grade is denoted by letters.
4) Structure:-Structure of grinding wheel represents the grain spacing. It can be open or dense .It
is generally denoted by number. Open structures are used for high stock removal and produces
rough finish. Dense structures are used for precision forms and profile grinding.
(The range for various characteristics is given in example)
Example:-
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b) What is ‘Lapping Operation’? Explain in detail the procedure of ‘Lapping Operation’.
Define- 2 marks, Diagram(any one)-2 marks, Desciption-4 marks
Lapping is a low pressure abrading process which is employed as a final finishing operation.
Desription-Lapping is performed manually or by machine by charging a lap made of soft material
with abrasive particles and rubbing it over the work piece surface with slight pressure. Charging
of lap means to embed the abrasive grains into its surface. The pressure is applied on the lap and
is moved with the loose abrasive between the lap and the work, lap remove the work till the work
confirms to the profile of the lap. The surface produced is dull in view of the random scratched
pattern.
The lap materials generally used are cast iron, soft steel, bronze and brass. Special
lubricants and bonding agent generally called vehicles are used during the process. The lubricants
used are water soluble cutting fluids, vegetable oils, mineral oils and grease. The lapping speed is
100-250 m/min. The material removed depends upon the lapping speed. Higher lapping allowance
requires higher speeds. The lapping pressure applied is 0.01 to 0.03 mpa for soft material and 0.07
mpa fore hard materials.
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The quality of surface finish and the extent of dimensional accuracy achieved mainly
depends upon- i) The type of lap material ii) the lapping medium iii) speed of lapping motion and
pressure applied and iv) material to be lapped.
Lapping can be carried out on flat, cylindrical surfaces.
c) Explain in brief following processes
i) Burnishing ii) Buffing
i) Burnishing (2 marks- Diagram, 2 marks- description) any other burnishing operation can
also be accepted.
Burnishing is a cold working process, by which improvement in surface finish, dimensional
accuracy and work hardening can be done. Roller burnishing improves surface finish by removing
scratches, tool marks and pits. It is a finishing operation and is normally done on parts which are
turned, reamed, or ground. Surfaces that could be burnished include external and internal
cylindrical surfaces, external and internal tapered surfaces, spherical surfaces and circular flat
surfaces. Machines normally used for burnishing operations can be drill press lathes, boring
machines, automatic bar chucking machines, multi spindle machines, or even special purpose
transfer machines. All type of soft or hard metals can be roller burnished.
ii) Buffing- (2 marks- Diagram, 2 marks- description)
Buffing is used to give much higher lustrous, reflective finish that cannot be obtained by
polishing. The buffing process consists in applying a very fine abrasive with a rotating wheel.
Buffing wheels are made of felts pressed and glued layers of duck or other cloth, and also of
leather. The abrasive is mixed with a binder and is applied either on the buffing wheel or on the
work. The buffing wheel rotates with high peripheral speed. The abrasive may consists of iron
oxide, chromium oxide, etc.
Any other suitable diagram may be considered.
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Q.6
a) State the advantages of gear finishing operations
1 mark each (any four)
i) Gear shaving is a corrective processes, it make a good gear better.
Ii) Gear lapping is a process of refining the gear element after the heat treatment operation.
iii) Gear grinding is a finishing process to remove considerable amount of metal after heat
treatment operation to obtain predetermined quality gear.
iv) Gear burnishing is a cold working process, it improves the surface finish.
v) Gear tooth honing is a finishing method for hardened gears and is intended to reduce the noise
of spur gear or helical gears.
b) Enlist different types of grinding wheels. State their application 1 mark each (any four)
Following are the different types of grinding wheels and their applicationsi) Straight- used for producing cylindrical, centreless and surface grinding operation.
ii) Recessed one side – used for producing cylindrical, centreless and surface grinding operation.
iii) Saucer- used for sharpening of circular or band saws.
iv) Straight cup- used for producing flat surfaces.
v) Cylinder – used for producing flat surfaces.
vi) Recessed two sides – used for producing cylindrical, centreless and surface grinding operation.
vii) Flaring cup- used for grinding in tool rooms.
viii) Dish- Used for tool room work
c) What are the various operations to be performed on grinding machine? 1 mark each
(any four)
Surface grinding, Cylindrical grinding, Taper grinding, Face grinding, Plunger cylindrical
grinding, Form grinding, Internal traverse grinding, Internal Plunger grinding, Internal taper
grinding.
d) State the necessity of super finishing processes. ( 04 marks)
-The dimensional and geometrical accuracies obtained by normal methods of machining like
turning, milling, etc are limited. The geometrical errors include circularity, cylindricity, flatness
and parallelism of functional surface. Also the surface finish has a vital influence on most
important functional properties such as wear resistance, fatigue strength, corrosion resistance and
power losses due to friction. Poor surface finish will lead to the rupture of oil films on the micro
irregularities present on the machined surface leads to a dry friction, and results in excessive wear
of the rubbing surface. Therefore super finishing processes are employed in machining the surface
of many critical components to obtain a very high surface finish or high dimensional and
geometrical accuracies.
e) Enlist different types of plastics
- i) Thermosetting plastics
(Types- 2 marks, Two Examples of each – 2
marks)
Phenol formaldehyde, Urea formaldehyde, Phenol furfural, Melamine Formaldehyde, Epoxides or
Epoxy resins, Silicones, Polyesters, Alkyds, Polyurethanes.
ii) Thermoplastics
Cellulose nitride, Cellulose acetates, Cellulose acetate-butyrate, Ethyl cellulose, Cellophane,
Cellulose propionate.
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MAHARASHTRA STATE BOARD OF TECHNICAL EDUCATION
(Autonomous)
(ISO/IEC - 27001 - 2005 Certified)
WINTER – 12 EXAMINATION
Subject Code : 12091
Model Answer
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f) Explain in brief ‘Injection Moulding’ process.
marks)
(Diagram- 2 marks, Description- 2
The process is illustrated in fig. the powdered plastic granules are first heated to drive off moisture
and then fed into the hopper. When the ram is drawn back, some of the powder granules drop
down into the chamber. After closing the mould the ram is moved forward, applying pressure
behind the powder. This compresses the material and forces it forward through the thin space left
around the heated torpedo. The material being in contact with the heated surface of the torpedo
and the chamber and at the same time being under compression softens and is forced into the
water cooled mould through the nozzle. During heating in the chamber the temperature of the
material rises to between 177 o c and 274o c. After the plastic has been cooled and sufficiently
hardened in the mould, the mould is opened and the produced part removed out.
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