General Metal Work
Table of Contents
General Metal Work...........................................................................................................................................1
GENERAL SURVEY...............................................................................................................................1
1. METALS AND THEIR PROPERTIES.................................................................................................5
1.1 Classification of Metals..............................................................................................................5
1.2 Identification of Metals (Examples)............................................................................................5
1.3 Properties of Metals...................................................................................................................7
1.4 Shapes and Sizes of Metal......................................................................................................11
2. TECHNICAL DRAWING...................................................................................................................12
2.1 Introduction into Technical Drawing.........................................................................................12
2.2 Types of Lines..........................................................................................................................13
2.3 Drawing Paper with title block..................................................................................................14
2.4 Basic Rules..............................................................................................................................16
2.5 Drawing in three Elevations.....................................................................................................19
3. METROLOGY...................................................................................................................................20
3.1 Metric System..........................................................................................................................20
3.2 Inch System.............................................................................................................................22
3.3 Metrology Introduction..............................................................................................................22
3.4 Common Measuring Tasks......................................................................................................22
3.5 Measuring Equipment..............................................................................................................23
4. FITS AND ISO TOLERANCES.........................................................................................................33
5. LAYING OUT....................................................................................................................................36
5.1 Layout Tools and Accessories.................................................................................................36
5.2 Layout Procedure.....................................................................................................................37
6. BENCH WORK TOOLS....................................................................................................................39
6.1 Work Bench..............................................................................................................................40
6.2 Bench Vise...............................................................................................................................40
6.3 Hand Hacksaw.........................................................................................................................41
6.4 Chisel Tools.............................................................................................................................42
6.5 Files..........................................................................................................................................43
6.6 Hammer...................................................................................................................................46
Bench Work Exercise.....................................................................................................................47
Bench Work Exercise − New..........................................................................................................53
7. PRINCIPLES OF MECHANICAL METAL CUTTING........................................................................60
7.1 Classification of Metal Cutting Processes................................................................................60
7.2 Angles of tools..........................................................................................................................60
7.3 Cutting Tool Guideline..............................................................................................................62
8. DRILLING.........................................................................................................................................62
8.1 Drill Press.................................................................................................................................62
8.2 Twist drill..................................................................................................................................64
8.3 Different Drill Press Operations................................................................................................68
8.4 Facts and Problems.................................................................................................................69
8.5 Drill Press Safety......................................................................................................................70
9. CUTTING THREADS WITH TAP & DIES.........................................................................................71
9.1 Main Parts of a Screw Thread..................................................................................................71
9.2 Hand Tapping...........................................................................................................................71
9.3 Threading Dies.........................................................................................................................74
10. SHARPENING TOOLS...................................................................................................................76
10.1 Bench Grinder or Pedestal Grinder........................................................................................76
10.2 Sharpening Tools...................................................................................................................77
10.3 Safety Precautions:................................................................................................................78
LIST OF NEEDED RESSOURCES FOR “GENERAL METAL” COURSE...........................................78
11. APPENDIX......................................................................................................................................79
APPENDIX NO. 1...........................................................................................................................79
APPENDIX NO. 2...........................................................................................................................80
GENERAL METAL WORK − FINAL TEST...........................................................................................81
i
ii
General Metal Work
With technical assistance from:
GERMAN DEVELOPMENT SERVICE
August 2000
Dear Reader,
I would like to comment this handout, because otherwise you might get a little confused while studying it.
The most important thing to know is, that this handout is developed for a non−formal Training Center. The
participating government officials and the involved companies were not interested in long−term courses. So, I
had to respect the wish of my project partners for a course with this length and was limited on the most
important subjects.
One or two of the modules are still under construction. Sorry for this.
DED − Development Worker
GENERAL SURVEY
TARGET PARTICIPANTS
• min 18 years old, High school graduates, no experience needed
LENGTH OF COURSE
120 hours / 15 days
OBJECTIVES
At the end of the course, the participants should be able to:
• Distinguish different metals and their properties and know the most common shapes of
metals
• Read and draft simple blue prints in order to fabricate workpieces to the required
specification
• Know how to measure, use the most important measuring tools and prevent the most
common mistakes while measuring
• Understand the importance of limits and fits in fabrication and know how to use them
• Lay out some workpieces with the necessary tools
• Understand the basics of angles of cutting tools
• Properly use hand hacksaw, file, chisel, hammer and other hand tools
• Know the process of drilling with a drill press and the needed tools and equipment
• Know how to sharpen tools using the bench grinder
• Cut internal and external threads with taps and dies and know how to prepare the workpiece
1
• Make use of different power tools typically used in a metal workshop
• Know how to use SMAW welding machine while welding mild steel
• Cut metals with Oxy−Acetylene cutting outfit
• Know and use the proper safety procedures and equipment
COURSE OUTLINE
THEORY (30%)
• Metals and their properties
• Various types of drawings,
scales, views, lines, symbols of
blue prints
• Measuring tools and measuring
errors.
• Metric and inch system
• Procedure of laying out
• Limits and fits
• Principles of metal cutting and
cutting angles of tools
• Bench and hand tools
• Drilling operation, threading and
reaming
• Sharpening tools using bench
grinder
• Cutting and grinding with power
tools
• SMAW welding process
• Oxy−Acetylene cutting
• Safety procedures and
equipment
HANDS−ON TRAINING (70%)
METHOD
• Draw and read some simple drawings
• Use measuring tools like steel rule, vernier
calibers, micrometer, protractor
• Use laying out tools like scriber, divider, center
punch, try square
• Make use of hand hacksaw and files while
preparing workpieces following the
specifications of blue prints
• Make use of a drill press and the necessary
equipment. Know how to calculate the RPM for
drilling
• Sharpen tools like scriber, center punch, chisel,
drill bits
• Experience the different power tools like bench
grinder, power hacksaw, chop saw, angle and
die grinder, drill
• SMAW welding exercises (mild steel with
different joints and various positions)
• Correct welding defects
• Oxy−Acetylene cutting exercises
Lectures/Discussion
Practical Sessions
Case studies
Teaching Videos
Time Frame Plan of “General METAL Work” − Course
(Zero skills level − Course Duration 120 hours)
Topic
Theory
? Methodology
Resources
Needed
Hours
Hands−On
Training
(Practical
Sessions)
Hours
Total
Hours
Orientation
• Training Overview
?
Lecture/Discussion
Manuals
General, Policy and
Procedure
1.0 Familiarization
tour to the
workplace
1.0
2.0
(2.0)
Work Attitude
• Work Attitude and
“Time is Money”
?
Lecture/Discussion
2.0
0.0
2.0
(4.0)
?
Lecture/Discussion
? Demonstration
Training Handout
Assorted
Samples of metals
2.0
0.0
2.0
(6.0)
4.0
8.0
Metals and
• Property definition
their Properties • Ferrous metals
• Nonferrous metals
and nonferrous
alloys
• Identification of
metals
• Shapes and sizes
of metals
2
Technical
Drawing
• Tools needed for
drawing
• Types of drawings
and views
• Types of lines
• Dimensioning
• Limits
• Scaling
• Basic Drafting
symbols
?
Lecture/Discussion
? Demonstration
Training Handout
Samples of blue
prints
Self practice
exercises in
reading and
drafting blue
prints and
preparing
different
workpieces
Measurement
• Metric and Inch
System
• Measuring tools
and care (Steel rules,
Vernier calipers,
Micrometers,
compass, Height
Gauges)
• Inspection of
measuring tools
?
Lecture/Discussion
? Demonstration
Training Handout
Samples of
Measuring tools
4.0 Self practice
exercises in
measuring
different
samples
6.0
10.0
(28.0)
Limits and Fits
• Interchangeability,
types of fits, limits of
tolerance on
technical drawings
?
Lecture/Discussion
? Training Handout
2.0
0.0
2.0
(30.0)
Laying Out
• Types of laying out
• Layout Equipment
and tools (Surface
plate, Combination
square, Scriber,
Center punch,
Divider, Steel rule,
Protractor, surface
gauge)
• Layout Accessories
(Angle Plate,
V−Blocks, Vernier
height gauge,
machine lay out)
?
Lecture/Discussion
? Demonstration
Training Handout
Samples of
Laying tools
2.0 Self practice
exercises in
laying out
different
workpieces
3.0
5.0
(35.0)
Bench Work
• Explain the use of
bench vise, hammer,
hand hacksaw, file,
chisel, letter stamp,
anvil
?
Lecture/Discussion
? Demonstration
Training Handout
Samples of
handtools
1.0 Bench work
exercise (MS
plate 180mm ×
100mm ×
10mm)
20.0
21.0
(56.0)
Principles of
Metal Cutting
• Machineability of
metals
• Cutting tool design
?
Lecture/Discussion
? Demonstration
Training Handout
3.0
0.0
3.0
(59.0)
Drill Press,
drilling tools,
drilling
operation
• Types of drill press
and the important
parts
• Tool holding device
and taper shank
tools
• Twist drills
(materials, sizes,
cutting speeds and
?
Lecture/Discussion
? Demonstration
Training Handout
Assorted
Samples of drill bits
3.0 Drilling exercise
(MS plate
180mm ×
100mm ×
10mm)
5.0
8.0
(67.0)
3
12.0
(18.0)
feeds)
• Machine vise, drill
press operation,
Cutting fluid,
countersinking,
counterboring
Threading
• Hand taps and tap
wrenches
• Tap drill size and
taping a hole
• Treading dies and
holder
• Treading lubricants
?
Lecture/Discussion
? Demonstration
Training Handout
1.0 Exercise for tap
and die
3.0
4.0
(71.0)
Resharpening
tools
• Explain bench
grinder
• Sharpen tools like
chisel, center punch,
scriber, drill bit
• Safety, care and
maintenance of
bench grinder
?
Lecture/Discussion
? Demonstration
Training Handout
1.0 Self practice
exercises in
resharpening
different tools
3.0
4.0
(75.0)
Cutting with
Power Tools
• Explain power
hacksaw and chop
saw
• Process on cutting
with power hacksaw
and chop saw
• Safety, care and
maintenance of
power hacksaw and
chop saw
?
Lecture/Discussion
? Demonstration
Training Handout
1.0 • Self practice
exercises in
cutting different
shapes of
metals
• Hands on
training in
maintain the
machines and
in mount and
dismount
hacksaw blade
and cutting disc
3.0
4.0
(79.0)
SMAW Welding
Fundamentals
and its
Processes
• Definition of the
various types of the
most common
welding technologies
• Power Sources
• SMAW Processes
• Tools and
equipment
?
Lecture/Discussion
Training Handout
Teaching Video
2.0
0.0
2.0
(81.0)
SMAW Welding
Electrodes
Types of electrodes
(mild steel, low
hydrogen electrode)
?
Lecture/Discussion
Training Handout
Teaching Video
2.0
0.0
2.0
(83.0)
Welding
Processes in
Various
Positions
• Striking the arc
• The most common
types of joints (Butt,
T, lap, corner, edge)
• The most common
types of grooves
(Square, beveled, V,
double V)
• Welding positions
(flat, horizontal,
vertical, overhead)
? Demonstration
?
Lecture/Discussion
Training Handout
Teaching Video
3.0 • Setting up the
equipment
• Weld with
different types
of mild steel
electrodes
• Prepare metal
plates and
grooves for
welding
• Weld
22.0
25.0
(108.0)
4
• Manipulation of
electrode
standardized
workpieces
Identification of • E.g. Incomplete
Welding
penetration, slag
Defects
inclusion, undercut,
spatters
?
Lecture/Discussion
Training Handout
Sample of
workpiece
1.0 Analyze welding
defects and
correct them
during the
practical work
3.0
4.0
(112.0)
Oxy−Acetylene
Cutting
?
Lecture/Discussion
? Demonstration
Training Handout
1.0 Cutting
Exercises
3.0
4.0
(116.0)
?
Lecture/Discussion
? Demonstration
Training Handout
4.0
0.0
4.0
(120.0)
40
80
120
• Types of gas for
cutting metals
• Gas cylinder, gas
flow meter and
pressure regulator
• Cutting tools
• Cutting process
Safety
• Safety in the
(included in the workshop
previous
topics)
Total
1. METALS AND THEIR PROPERTIES
1.1 Classification of Metals
Steels are the most important ferrous metals used in machine shop work. They are generally classified by
their carbon content. It can be custom−made to fit a wide range of requirements. By using various chemical
and alloying elements, steels with many different properties can be produced.
1.2 Identification of Metals (Examples)
Metal
Cast Iron (C.I.)
5
Carbon
Content %
2.5 to 3.5
Appearance
Grey, rough sandy surface
Uses
Parts of machines, such as lathe
beds, water pump pitcher type, etc.
Machine Steel
(M.S.)
0.10 to 0.30
Black, scaly surface
Bolts, rivets, nuts, machine parts
Cold Rolled
(C.R.S.)
0.10 to 0.30
Dull silver, smooth surface
Shafting, bolts, screws, nuts
Tool steel (T.S.)
0.60 to 1.5
Black, glossy
Drills, taps, dies, tools
High Speed
Steel (H.S.S.)
Alloy Steel
Black, glossy
Dies, taps, tools, drills, toolbits
Brass
/
Yellow (various shades), rough
if cast, smooth if rolled
Bushings pump parts, ornamental
work
Copper
/
Red−brown, rough if cast,
smooth if rolled
Soldering irons, electric wire, water
pipes
Metals are usually identified by one of the following four methods:
• By their appearance
• By spark testing
• By manufacturer’s stamp
• By a code color painted on the bar.
Exercise Sheet
Classify the materials. Please mark your answer by a “X”.
Metals
Ferrous Metal
Nonferrous Metal
Non−Metals
Natural Material
Artificial
Material
Wood
Aluminum
Leather
Glass
Copper
Mild Steel
Cast Iron
Rubber
Ore
Brass
Ceramics
Tool Steel
Bronze
Lead
PVC
Teflon
Tin
Stainless Steel
6
Materials used in Car Production
Use one of these expressions to complete the statements below:
“covered with” or “made of” or “contain(s)”
The pipes of the radiator ………………………. copper.
The bumper …………………………………… chromium.
The door handles ……………………………… zinc.
The cables ……………………………………... plastic.
The windscreen ……………………………….. glass.
The battery ……………………………………. lead.
The pistons ……………………………………. aluminum.
The cylinder block ……………………………. cast iron.
1.3 Properties of Metals
To better understand the use of the various metals, you should be familiar with the following metallic
properties:
1.3.1 Physical Properties:
Melting Point:
The melting point is the temperature at which a material starts to melt.
Ferrous
1,536 degree Celsius
Copper
1,083 degree Celsius
Lead
327 degree Celsius
Aluminum
658 degree Celsius
Tin
232 degree Celsius
Tungsten
3,387 degree Celsius
Electrical Conductivity:
The electrical conductivity describes the ability of a material to conduct electricity.
Copper
100%
Silver
106%
Lead
8%
Aluminum
62%
Ferrous
17%
Zinc
29%
7
Density:
The density (kg/dm3) of a material gives the quotient of mass and volume of a body.
Water
1.00
Copper
8.90
Lead
11.30
Aluminum
2.70
Steel
7.85
Tungsten
19.27
Thermal longitudinal expansion:
To express the thermal longitudinal expansion, there is a coefficient that gives for each material the expansion
of a body with the length of 1 Meter at a change of temperature of 1 degree Celsius.
1.3.2 Mechanical −Technological Properties:
Elasticity:
Is the ability of a metal to return to its original shape after being
distorted. Properly heat−treated springs are good examples of
elastic materials.
Ductility:
Is the ability of a metal to be permanently deformed without
breaking. Metals such as copper and machine steel, which may be
drawn into wire, are ductile materials
8
Tensile Strength:
The ability of material to resist fracture under tensile load.
Compressive Strength:
The ability of a material to withstand heavy compressive load.
Brittleness:
Is the property of a metal that allows no permanent distortion
before breaking. Cast iron is a brittle metal; it will break rather than
bend under shock or impact.
Toughness:
Is the ability of metals to withstand shock or impact. Toughness is
the opposite of brittleness.
Shear Strength:
The ability of a material to resist fracture under shear load.
Flexural Strength:
The ability of a metal to resist under flexural force.
Torsional Strength:
The ability of a metal to resist torsional force.
9
Collapsing Stress:
The ability of a metal with a slim form to resist axial directed force.
Hardness:
The ability of metal to withstand abrasion or penetration.
1.3.3 Manufacturing − Technological Properties:
Weldability:
Means the ability to weld two metals together. The grade of
weldability depends on the content of carbon. Steels with a content
of max. 0.22% are more or less good weldable.
Machinability:
Indicates how easy or difficult materials can be machined.
Malleability:
Is the property of metals that allows it to be hammered or rolled into
other sides and shapes.
Castability:
Is the property of metals that allows it to be molten and after it to be
casted without any pores.
Hardenability:
Is the property of iron metals that allows it to increase the
hardening through structural transformations.
1.3.4 Chemical Properties:
10
Corrosion Resistance:
Is the ability of a material to resist the attack of water, gases, acids or
other chemicals.
1.4 Shapes and Sizes of Metal
Due to the wide variety of work performed in a metal shop and the necessity of conserving time, as well as
reducing the amount of metal cut into steel chips, metals are manufactured in a wide variety of shapes and
sizes.
There is a proper method for specifying the sizes and dimensions of metal when ordering:
11
Flat−bar:
Thickness × Width × Length
Round−bar:
Diameter × Length
Square−bar:
Width × Length
Angle−bar:
Thickness × Width × Length
Hexagon−bar:
Diameter × Length (or Distance Across Flats ×
Length)
Pipe:
Diameter × Schedule × Length # 20 is thinner
than # 40
Square−tubing:
Thickness × Width × Length
Channel−Bar:
Width × Height × Length
I−Beam:
Length × Thickness × pounds
Z−Bar:
Width × Length
T−Bar:
Width × Length
Metal Sheet:
Gauge × Width × Length
2. TECHNICAL DRAWING
A technical drawing, sometimes referred to us as a drawing or print, is the language used for technical
communication. It depends on the job how exactly the drawing should be made. Sometimes it is enough to
sketch with freehand lines, but when it comes to more important parts the draft should be made very exactly.
2.1 Introduction into Technical Drawing
Drawing Equipment
The basic equipment is:
• Drawing board
• T−Square
• Drawing paper
• Compass
• Protractor
• Pencils
• Eraser
Drawing Paper sizes
ISO
mm
A0
A1
A2
A3
A4
A5
A6
841×1189 594×841 420×594 297×420 210×297 148×210 105×148
Scale Size
12
Scale is used to indicate the ratio of the drawing size to the actual size of the part. Scaling is often necessary
to enlarge small parts for clarity and to have room for dimensions and other details. Large objects are often
drawn at a reduced scale in order to get the necessary information to fit a convenient size sheet of paper. The
scale is generally found in the title block of a drawing.
The dimensions shown on the drawing give the correct size of the part required. The actual drawing should
never be measured to determine that size to be machined.
2.2 Types of Lines
Various standard line styles and widths are used on technical drawings by the designer to precisely specify
what is required. The examples below is the so called “alphabet of lines”:
Standard lines used for technical drawings:
Type
Description
Use
Free−hand
line
Thin black lines
0,25 to
0,35
Object line
Thick black lines
0,5 to 0,7
Indicate the
visible form
or edges of
an object
Thin unbroken
line
Thin black line
0,25 to
0,35
Shading
line, Thread
line,
Diagonal
line
Hidden line
Medium−weight
black lines (dash:
approx. 4 mm,
gap: 1 mm)
0,35 to 0,5
Indicate
hidden
contours of
an object
Center line
Thin lines with
alternating long
lines and short
dashes (dash:
approx. 10 mm,
gap: 1 mm)
0,5 to 0,7
Indicate
centers of
holes,
cylindrical
objects, and
other
sections
0,25 to
0,35
Indicate
dimensions
of an object
Dimension line Thin black lines
with arrowhead at
each end.
13
Thickness
mm
Sketches;
break line
Cutting−plane
line
Thick black line
(dash: approx. 7
mm, gap: 1 mm)
0,5 to 0,7
Show
imagined
section
Cross−section
line
Fine evenly
spaced parallel
lines at 45°. Line
spacing is in
proportion to the
part size
0,25 to
0,35
Show
surfaces
exposed
when a
section is
cut
Exercise Sheet
Fill up the boxes with the given line type
2.3 Drawing Paper with title block
14
Exercise Sheet
1. Draw and dimension the object below using the given measurements. Use a piece of paper with a
title block.
2. Draw and dimension the object below using the given measurements. Use a piece of paper with a
title block.
15
2.4 Basic Rules
Dimensions are entered in millimeters without measures.
Dimension lines must have a distance of about 10 mm from
the object edge and 7 mm from parallel dimension lines. The
dimensions should be placed above the dimension lines and
should be staggered.
Dimensions must be either read from below or from the
right. For small dimensions the arrows are placed outside.
Symmetrical workpieces are dimensioned symmetrical to the
center line which extends 2−3 mm beyond the object edge.
16
Simple workpieces are mostly drawn in front elevation only.
If an elevation in which the area of a circle appears as a
straight line is to be dimensioned, the diameter symbol is to
be placed in front of the dimension figure.
If the circle is shown in the elevation, then it is not necessary
to draw the diameter symbol.
The diameter is shown by two dimension arrows on the
circumference or drawn on the extension lines of the circle. In
this cases no diameter symbol will be used.
A radius is symbolized by R and has only one dimension
arrow at the circumference. The center point is fixed by the
crossing of center lines.
Concealed edges are drawn as dash lines. The length of
each dash depends on the size of the drawing.
Dash lines start and end with a dash at the object edges.
If visible and concealed edges coincide, the visible edges are
drawn.
17
Section views are used to show the interior form of an object
that could not be shown clearly by conventional methods.
The section areas are shaded, not the hollow spaces.
The smaller the section area the closer the shading lines.
In order to insert dimension figures the shading has to be
broken.
The shading lines are thin unbroken lines, which are angled
at 45 degree to the center line or angled to the base edge.
Assembled workpieces are identified by opposite or varied
shading. Section areas of one object are always shaded in
the same direction.
The outer diameter of a bolt thread is drawn as an object
line, the core diameter as a thin unbroken line. The distance
between the thick and thin lines represents the thread
diameter.
Looking in direction of the shaft end the core diameter
appears as a three−quarter circle in any position.
18
The ends of screws are normally 45 degree chamfered.
The core diameter of the internal thread is drawn as an
object line, the outer diameter as a thin unbroken line.
All lines of concealed thread are drawn as invisible edges.
The thin three−quarter circle becomes a full circle shown in
broken line.
To be dimensioned are: Outer diameter (e.g. M 10 or UNC ¾)
Useful length of thread Length of shaft with end, or
respectively depth of core hole without drill cone.
2.5 Drawing in three Elevations
Sometimes it is necessary to draft workpieces in three elevations to show all important parts of it.
19
3. METROLOGY
Over 90% of all countries in the world are presently using the Metric System. But there are still some
countries using the Inch System (e.g. United States, Canada, and England). With the reality of global
manufacturing continually expanding, the need for metal workers in both systems of measurement will
continue to grow.
3.1 Metric System
The metric system uses the meter and linear units based on the meter as its standards of measure. At the
General Conference on Weights and Measures in October, 1983, the meter, defined as the distance traveled
by light in a vacuum during 1/299,792,458 of a second, was approved as a world standard.
20
All multiplies and subdivisions of the meter are directly related to the meter by a factor of ten. This makes it
easy to use the decimal system for calculations involving metric units.
Kilometer
= km
1 km
=
1,000 m
Meter
= m
1m
=
10 dm =
Decimeter
= dm
1 dm
=
10 cm =
Centimeter
= cm
1 cm
=
10 mm
Millimeter
= mm
1 mm
=
1,000 mm
Micrometer
= mm
100 cm =
100 mm
3.1.1 Exercises − Metric System
Change into smaller units
1m
=
2.5 m
10 dm
=
100 cm
=
1,000
mm
dm
=
cm
=
mm
0.9 m
=
dm
=
cm
=
mm
1.2 m
=
dm
=
cm
=
mm
0.1 m
=
dm
=
cm
=
mm
Change into larger units
100 mm
=
10 cm =
1 dm =
0.1 m
25 mm
=
cm =
dm =
m
120 mm
=
cm =
dm =
m
19 mm
=
cm =
dm =
m
386 mm
=
cm =
dm =
m
Summing Up
20 cm +
10 dm +
30 mm +
25 cm =
1,48
m
10 cm +
5 dm +
28 mm +
30.5 cm =
mm
38 mm +
42 cm +
0.6 dm +
0.9 m =
cm
5.5 dm +
122 mm +
44 cm +
1.2 m =
dm
2.2 m +
86 cm +
77 cm +
333 mm =
m
0.1 mm +
1.2 cm +
9.86 cm +
55.6 mm =
mm
Mixed Operations
1m +
37 mm −
5 dm +
40 cm =
937 cm
1.47 m −
37 mm −
1.8 dm +
36.5 cm =
cm
96 mm −
3.8 cm +
1.36 m +
98 dm =
dm
0.4 cm −
12 mm +
1.55 m −
8.4 dm =
m
11 cm +
11 mm +
1.1 dm +
1.11 m =
m
21
1,000 mm
19.4 dm −
87.5 cm +
1.36 m −
94 mm =
dm
Conversion from Metric to Inch or opposite
1 millimeter
=
0.0394 inch
1 inch
=
25.4
millimeters
1 centimeter
=
0.3937 inch
1 inch
=
2.54
centimeters
1 meter
=
39.37 inches
1 foot
=
0.3048
meter
3.2 Inch System
Unlike the Metric System, within the Inch System there is no relationship of other linear units to the base inch
unit. The values of yard, rod, mile, etc. have to be studied and kept in memory in order to use them. The inch
can be dived in halves (1/2), quarters (1/4), eighths (1/8), sixteenth (1/16), thirty−seconds (1/32), sixty−fourth
(1/64), tenth, hundreds, thousandth, ten−thousands etc.
3.3 Metrology Introduction
Engineering metrology is defined as the measurement of dimensions: length, thickness, diameter, taper,
angle, flatness, profiles and others.
An important aspect of metrology in manufacturing processes is dimensional tolerances. That is, the
permissible variation in the dimensions of a part. Tolerances are important not only for proper functionings
of products, they also have a major economic impact on manufacturing costs. The smaller we make the
tolerances, the higher the production costs. These and related aspects of tolerances and tolerancing are
described later on in this course.
3.4 Common Measuring Tasks
Inside − Outside
Height − Depth
Diameter
22
Distance
Angle
Taper
Gear
Surface
Geometrical Form and Position
3.5 Measuring Equipment
A modern industrial fabrication could not function without precise measuring equipment. The parts produced
are useless if they are not made to the exact sizes specified by the customer.
23
3.5.1 Care of Measurement Tools
Proper care of measuring tools and instruments is very important to maintain the accuracy and quality of
these tools. Precision measuring tools and instruments are expensive and should be treated with care,
otherwise their accuracy can be destroyed.
• Never drop a measuring tool.
• Keep measuring tools away from chips, welding and grinding sparks.
• Never place measuring tools on oily or dirty surfaces.
• Store measuring tools in separate boxes to avoid scratches, nicks, or dents.
• Clean the tools and apply a light film of oil on the handling surfaces before putting them
away.
3.5.2 Sample of Gauges
Outside Radius Gauge
Inside Radius Gauge
Angle Form Gauge
Limit Snap Gauge
24
Thread Gauge
Angle Form Gauge
Limit Plug Gauge
Outside Thread−Ring Gauge
Inside Thread−Plug Gauge
3.5.3 Indirect Reading Instruments
Inside and Outside Calipers are comparison tools used to make approximate measurements of the outside
diameter of round workpieces. The caliper cannot be read directly and its setting must be checked with a rule
or a vernier caliper.
25
Inside caliper with curved legs, a spring, and an adjusting nut
Outside caliper with curved legs, a spring, and an adjusting nut
3.5.4 Angle Measuring Instruments
With a simple Protractor the measuring arm can be set against a circular degree scale from 0 degree to 180
degree. The measuring error is around 1 degree.
With a more precise Universal Bevel Protractor angular measurements can be carried out with an accuracy of
5 minutes.
Simple Protractor
Universal Bevel Protractor
26
3.5.5 Comparative Length−Measuring Instruments
These instruments compare dimensions, hence the word comparative.
Dial Caliper
Digital Caliper
Digital Micrometer
27
Dial Gauge
3.5.6 Direct Reading Instruments
Steel Rules
Steel rules are the most common linear measuring tools and are available in the metric or inch system. Metric
rules are graduated in both millimeters and half−millimeters. Some rules are available with both inch and
millimeter graduation.
28
Exercise Sheet − Measuring with the Steel Rule
Measure all given shapes in metric and inch
Vernier Calipers
Vernier calipers are precision measuring instruments used to make internal, external and depth
measurements. Both systems metric and inch are available, and some styles of vernier caliper provide metric
readings on one side and inch readings on the other side.
The common size of verniers for machine shops are 200 mm, 250 mm and 300 mm. The precision depends
on the vernier scale. Common types provide an accuracy of either 0.05 mm or 0.02 mm. The example below
shows an accuracy of 0.05 mm.
How to read a Metric Vernier Caliper (accuracy 0.05 mm):
29
1. The last numbered division on the bar to the left of the zero on the vernier scale
represents the number of millimeters. In the example above the #2 (20 mm) is the last
number left of the zero on the vernier scale.
2. Count the graduations between the last number (#2) and the zero on the vernier scale. In
the example above there are 8 (8 mm) graduations between the #2 and the zero on the
vernier scale.
3. Locate the line on the vernier scale that aligns with a bar line. Divide the number below
the line by 10. In the example above it is the line with #7 (7/10=0.7 mm).
4. The measurement in the example above is 20 mm + 8 mm + 0.7 mm = 28.7 mm
Exercise Sheet − Read a Vernier Caliper with an accuracy 0.05 mm
30
Exercise Sheet − Read a Vernier Caliper with an accuracy 0.02 mm
Hands On − Measurement Exercise
Steel Ruler
Vernier Caliper
No. mm inch No. mm inch
1
1
2
2
3
3
4
4
5
5
6
6
7
7
8
8
9
9
10
10
11
11
12
12
31
13
13
14
14
15
15
16
16
17
17
Hands On − Measurement Exercise
Steel Ruler
Vernier Caliper
No. mm inch No. mm inch
1
1
2
2
3
3
4
4
5
5
6
6
7
7
8
8
9
9
10
10
11
11
32
4. FITS AND ISO TOLERANCES
Limits and Fits
In the world of manufacturing it is almost impossible to reach exactly the given dimension for a workpiece.
Therefore the off−sizes must be tolerated. To make sure, that all mating parts will fit each other they should
be fabricated within certain limits of nominal dimension.
Common Expressions in the world of manufacturing:
Nominal
The given size in the technical drawing
N
Upper Limit
The maximum allowed size.
UL
Lower Limit
The minimum allowed size.
LL
Upper Tolerance
Is the difference between Nominal and Upper Limit
UT
Lower Tolerance
Is the difference between Nominal and the Lower Limit
LT
Tolerance
Is the difference between the Limits
T
Shaft with a
nominal
dimension
of 20 mm
33
Shaft with
toleranced
dimension,
2 mm plus
and 2 mm
minus is
allowed.
UL = N +
UT
LL = N− LT
T = LT + UT
Limits − Exercise Sheet
Nominal
Dimension
Upper
Limit
(max. Æ)
Lower
Limit
(min. Æ)
Upper
Tolerance
Lower
Tolerance
Tolerance
20.00 mm
20.00 mm
20.00 mm
0.00 mm
0.00 mm
0.00 mm
20.00 mm
20.50 mm
20.00 mm
0.50 mm
0.00 mm
0.50 mm
20.00 mm
20.25 mm
19.75 mm
0.25 mm
0.25 mm
0.50 mm
20.00 mm
20.00 mm
19.80 mm
0.00 mm
0.20 mm
0.20 mm
20.00 mm
20.15 mm
19.95 mm
0.15 mm
0.05 mm
0.20 mm
20.00 mm
20.00 mm
19.95 mm
0.00 mm
0.05 mm
0.05 mm
20.00 mm
20.02 mm
19.99 mm
0.02 mm
0.01 mm
0.03 mm
20.00 mm
20.01 mm
19.99 mm
0.01 mm
0.01 mm
0.02 mm
34
20.00 mm
20.035
mm
20.00 mm
0.035 mm
0.00 mm
0.035 mm
20.00 mm
20.055
mm
20.045
mm
0.055 mm
0.045 mm
0.010 mm
Classes of Fits
Force Fit (Interference Fit)
Transition Fit
35
Loose Fit (Clearance Fit)
5. LAYING OUT
Laying out is the operation of scribing center locations, straight lines, arcs, circles, or contour lines on the
surface of a piece of metal to show the machinist the finished size and shape of the part to be manufactured.
The information regarding the size and shape of part is taken from a technical drawing. The care and
accuracy of the layout plays an important role in determining the accuracy of finished parts, since the
machinist uses these layout lines as a guide for machining.
5.1 Layout Tools and Accessories
Tools &
Accessories
Details
Surface Plate or
Marking Table
Is a plate or a table made of cast iron or of granite. It must be adjusted absolute
horizontally. Its surface must be perfect plane to ensure accurate scribing. To bring
workpieces to the correct position on the marking table there are some other devices
like prism, angle plate, V−Blocks and Parallels.
Steel Rule
Steel rules are the most common linear measuring tools and are available in the
metric or inch system. Metric rules are graduated in both millimeters and
half−millimeters. Some rules are available with both inch and millimeter graduation.
Scriber
A scriber is a layout tool used for drawing layout lines on a workpiece. They are
made of tool steel with hardened and tempered points. It is important that the point of
the scriber be as sharp as possible to produce clear, thin, layout lines.
Center Punch
Normally ground to an angle of 90 degree. Before drilling a hole the center must be
punched. To make a line more visible for cutting or oxy−acetylene cutting it is helpful
to punch the line.
Solid Square or
Try−Square
Is used for laying out workpiece in combination with steel rule and scriber. It is also
used to check the angles and the surfaces for flatness.
Divider
The divider is used to transfer length or circles to the workpiece. Dividers are
available with and without fixing devices.
Protractor
A simple protractor has a measuring range from 0 to 180 degree. The measuring
error is around 1 degree.
Surface Gauge or
Vernier Height
Gauge
Is normally used in combination with a surface plate and an angle plate to mark
parallel lines. Using the simple type, the height can be adjusted with a steel rule.
36
Angle Plate
An angle plate is a precision L−shaped tool usually made of hardened steel. All its
surfaces are ground to an accurate 90−degree angle and are square and parallel. It
is used to support workpieces on a 90−degree angle during the layout process.
V−Blocks or Prism
It is an accurate fabricated layout device to hold cylindrical workpieces during the
layout process. They have one or more accurate 90−degree V−slots.
5.2 Layout Procedure
5.2.1 Laying out with Try−Square and Steel Rule
1. Remove all burrs from the workpiece and clean it properly.
2. Start the layout from a square machined (or filed) surface.
3. Use a try−square and a steel rule.
4. Place the point of the sriber on the workpiece against the try−Square edge. Hold the
scriber 15 degree inclined away from the workpiece and in the direction in which it is to be
drawn.
37
5.2.2 Laying Out Circles with the Divider
1. Lay out the center of the circle
2. Punch the center of the circle
3. Adjust the divider to the proper radius while using a steel rule or a vernier caliber
4. Place one point of the divider in the center punch hole and give some force to this leg.
5. Move around the fixed leg and scratch the surface.
Laying out circles
Laying out parallel lines
5.2.3 Laying Out with Surface Gauge
38
5.2.4 Laying Out with Protractor
5.2.5 Center Punch Procedure
1. Make sure that the point of the punch is sharp before starting.
2. Hold the punch at a 45 degree angle and place the point carefully on the layout line.
3. Tilt the punch to a vertical position and strike it gently with a light hammer.
4. If the punch mark is not in the proper position, correct it as necessary.
6. BENCH WORK TOOLS
Even in the time of CNC technology it is important to know how to do bench work using different hand tools,
because still today bench work plays a big rule in machine maintenance or in metal fabrication.
39
This chapter will provide the trainee with the necessary knowledge about bench work. This includes the basic
tools as well as their proper use.
6.1 Work Bench
• The workbench should be sturdy and when possible fixed with the shop floor.
• It is advisable to use wood for the bench board.
• The height of the workbench should depend on the height of the craftsman.
• Keep the workbench clean. Put only the tools necessary for the work on it.
• Measuring tools should be all the time separated from the other tools. Place them accurately
on the wooden tray board.
6.2 Bench Vise
• The base of a bench vise is normally made of cast iron. The jaws are hardened. Clamping
soft workpieces requires covering the jaws with an aluminum sheet cover.
• The size of the bench vise is measured by the width of the jaws and the maximum opening
between the jaws.
• There are different types of bench vises available: With or without an anvil plate, with a pipe
clamping device, machine vise for drill press, and adjustable in any position within 360
degree.
40
6.3 Hand Hacksaw
A hand hacksaw mainly serves to separate materials and also to produce grooves and slits.
By moving the saw in the direction of cut (cutting motion) with simultaneous pressure on the saw (cutting
pressure), the teeth penetrate into the material and remove chips.
There are different hacksaw blades, depending on the metal to be cut, available:
Coarse:
for soft materials appr. 14 teeth per inch.
Medium: for normal material appr. 22 teeth per inch.
Fine:
for hard material appr. 32 teeth per inch.
In order to achieve a perfect cut, file with a triangular file a small notch beside the marking line to get a good
start, then place the saw with an angle of tilt (as shown in the picture below) and start with sawing.
41
Forward stroke with pressure. Return stroke without pressure. Use the full length of the saw blade.
Saw in a straight line along the marking line.
Work safety:
When sawing through reduce pressure on hand hacksaw just before the workpiece separate.
6.4 Chisel Tools
In chiseling the cutting edge of a chisel is driven into a workpiece by impact. A chisel must be harder than the
piece being worked. Most chisels are made of alloyed tool steels.
Flat Chisel
Wedge angle for soft materials 30 to 50 degree; for mild steel 60 to 70 degree; for alloyed steels 70 to 80
degree
Work Process:
• The workpiece must be properly clamped when chiseling.
• The chisel must be struck on the center of the head, in the direction of the axis of the chisel.
• The correct wedge angle must be maintained when grinding the chisel (measure with an
angle gauge). The tool must be cooled frequently when sharpening, so that it does not lose its
temper.
42
Shearing with a shearing chisel
The head of the chisel must be free of burrs and grease
6.5 Files
The file is a cutting tool to work materials. It has many cutting edges which are like small chisels (file teeth)
and are harder than the material being worked upon. For cutting metals normally Cross−Cut files are used.
These files have an overcut, and an upcut. When using a file, several cutting wedges always act at the same
time.
• To file different materials there are various coarses available, such as smooth−cut,
second−cut, and bastard cut.
43
• The length of the file body normally used is between 100 mm and 350 mm.
• The file handle is either from wood or from plastic.
Types of Files
1. Square File large
2. Flat File
3. Square File small
4. Triangle File
5. Round File
44
6. Half−Round File
7. Knife File
8. Flat−Triangle File
45
File Handling
• Clamp the workpiece as close as possible to the jaws of the vise. Use protective jaws
(Aluminum) to protect the workpiece.
• Start with a rough file for removing more material then take a smooth file to reach a good
surface.
• Forward stroke with pressure; Return stroke without pressure.
• Move with the file crosswise to control the area of filing.
• Clean the file from time to time (especially smooth files) with a wire brush to prevent messy
finishes.
• Never work with a file without a file grip.
• Make sure that the file grip is properly attached, that it has the right dimension and that it is
not splitted.
6.6 Hammer
• A hammer is used nearly in every operation related to metal works.
• They are made of cast steel or carbon steel.
• It mainly consists of a face, peen and body. The face and the peen are hardened and
tempered but the rest of the body is kept soft. A wooden handle is fitted in the eyehole of the
hammer with the help of a wedge. The wedge spreads the handle and fixes it inside the hole.
• Hammers are made in the size range of 25 Gram to 10 Kg.
• There are different types of hammer available:
Fitters hammer, Ball pane hammer, Rubber mallet, Plastic hammer, Wood
hammer, Sledge hammer, Claw hammer, Aluminum hammer, copper etc.,
46
Safety:
− The handle of a hammer should be dry and not greasy
− The surface of a handle should be smooth
− The face of a hammer should not be spotted, if it so then make it smooth by grinding
− Hold the hammer handle always nearer to its tail end.
Bench Work Exercise
Necessary material and tools for this exercise:
• 1 piece flatbar 200 mm × 102 mm × 10 mm
• steel rule 400 mm
• scriber
• center punch
• hammer 200 g
• protractor
47
• try square
• combination square
• vernier caliber 250 mm
• depth vernier caliber
• hand hacksaw
• flat file 250 mm rough and bastard
• triangular file 250 mm rough and bastard
• different twist drills
• different screw taps
• different countersink
• letter stamps
• chisel
Metal Plate − Working Step No. 1
1. Take a piece of flat bar with a measurement of 200 mm lengths and 105 mm width and 10
mm thickness.
2. Take the letter “A” stamp and stamp it as shown in the above drawing.
3. File surface of edge A even and remove all rust and forging scale. First use a rough file,
then for finishing the surface a bastard file. Control the evenness with the try square.
4. Layout lines from the left side as well as on the right side. Use edge A as a reference to put
the try square and scribe the lines.
5. Center punch the lines with at least 5 mm distance between the marking points.
6. Cut on the outer part of the lines using the hand hacksaw and leave at least 1mm
allowance for filing.
7. File the surfaces of edges B and D in a right angle to surface A. File the 1mm excess to
the size required.
8. File surface of edge C even and parallel to edge A to the size required. First use a rough
file, then for finishing the surface a bastard file.
Metal Plate − Working Step No. 2
48
1. Take a combination square and set 135 degrees angle using a protractor.
2. Put the combination square at edge A.
3. Scribe a line with the scriber.
4. Center punch the line with at least 5 mm distance between the marking points.
5. Cut on the outer part of the line using the hand hacksaw and leave at least 1mm allowance
for filing.
6. File the surface of edge B in an angle of 135 ° to surface A. File the 1mm excess to the
size required.
Metal Plate − Working Step No. 3
1. Take divider and steel rule for laying out the central point of radius = 40 mm.
49
2. For laying out, use surfaces “A” and “B” as basis.
3. Set the divider on 40 mm radius.
4. Scribe a circle on the left lower corner of the work piece.
5. Center punch with at least 5 mm distance between the marking points along the line.
6. Cut on the outer part of the layout line leaving 2 mm allowance for filing.
Metal Plate − Working Step No. 4
1. Lay out using surface “A” and “B” as a basis, scribe and punch following the illustration
given below on the right lower corner of the work piece.
2. Cut on the outer part of the layout line leaving 1 mm allowance for filing.
3. File the work piece and check if it is in the right measurement.
Metal Plate − Working Step No. 5
50
1. Lay out the two squares which are 30 mm × 30 mm and 20 mm × 20 mm as shown in the
drawing above using surface “A” and “B” as a basis.
2. Mark the squares exactly as shown in the drawing above.
3. Centerpunch the lines as shown in the drawing above.
4. Drill the punch mark of the inner square with a 8.5 mm twist drill.
Metal Plate − Working Step No. 6
1. Cut the bridge between the wholes using chisel and hammer.
2. File the outer square 30 mm × 30 mm using the necessary files.
3. Check if the filed square is parallel to surfaces “A”, “B”, “C” and “D”.
Metal Plate − Working Step No. 7
51
1. Mark a border line for the height of the letters and vertical line for each letter. For the width
let approximately 1 mm clearance both sides.
2. Adjust the letter stamp on the surface of the work piece.
3. Strike the letter stamp using a 200 g hammer.
Metal Plate − Working Step No. 8
1. Lay out the lines for drilling using the measurement given.
2. Punch all the mark for drilling.
Metal Plate − Working Step No. 9
52
1. Drill the holes with required twist drills.
2. Countersink both sides of holes with countersink tool.
3. Tap the threads with required screw taps.
4. Check the specifications for holes “1” and “2” in the complete technical drawing of the
workpiece.
Bench Work Exercise − New
53
Necessary material and tools for this exercise:
• 1 piece flatbar 100 mm × 100 mm × 10 mm
• steel rule 400 mm
• scriber
• center punch
• hammer 200 g
• protractor
• try square
• combination square
• vernier caliber 250 mm
• depth vernier caliber
• hand hacksaw
• flat file 250 mm smooth and rough
• triangular file 250 mm smooth and rough
• square file 250 mm smooth and rough
• different twist drills
• different screw taps
• different countersink
• letter stamps
• chisel
Metal Plate − Working Step No. 1
54
1. Take a piece of flat bar with a measurement of 100 mm lengths and 100 mm width and 10
mm thickness.
2. The fianl dimension of the workpiece should be 95 mm × 90 mm × 10 mm with a
tolerance of plus 0.2 mm and minus 0.2 mm.
3. Take the letter “A” stamp and stamp it as shown in the above drawing.
4. File surface of side A even and remove all rust and forging scale. First use a rough file,
then for finishing the surface a smooth file. Control the evenness with the try square.
5. Layout lines from the left side as well as on the right side. Use side A as a reference to put
the try square and scribe the lines.
6. Center punch the lines with at least 5 mm distance between the marking points.
7. Cut on the outer part of the lines using the hand hacksaw and leave at least 1mm
allowance for filing.
8. File the surfaces of sides B and D in a 90 degree angle to surface A. File the 1mm excess
to the size required.
9. File surface of edge C even and parallel to side A to the size required. First use a rough
file, then for finishing the surface a smooth file.
Metal Plate − Working Step No. 2
55
1. Take a combination square and set 135 degrees angle using a protractor.
2. Put the combination square at side A.
3. Scribe a line with the scriber.
4. Center punch the line with at least 5 mm distance between the marking points.
5. Cut on the outer part of the line using the hand hacksaw and leave at least 1mm allowance
for filing.
6. File the surface in an angle of 135 ° to surface A. File the 1mm excess to the size
required.
Metal Plate − Working Step No. 3
56
1. Take divider and steel rule for laying out the central point of radius = 40 mm.
2. To layout, use surfaces “A” and “D” as basis.
3. Set the divider on 40 mm radius.
4. Scribe a circle on the left lower corner of the work piece.
5. Center punch with at least 5 mm distance between the marking−points along the line.
6. Cut on the outer part of the layout line leaving 2 mm allowance for filing.
7. File the surface exactly following the marks.
Metal Plate − Working Step No. 4
1. Lay out the two squares which are 30 mm × 30 mm and 20 mm × 20 mm as shown in the
drawing above using surface “A” and “B” as your basis.
2. Mark the squares exactly as shown in the drawing above.
3. Centerpunch the lines as shown in the drawing above.
4. Drill the punch mark of the inner square with 8.5 mm twist drill.
Metal Plate − Working Step No. 5
57
1. Cut the bridge between the wholes using chisel and hammer.
2. File the outer square 30 mm × 30 mm using the necessary files.
3. Check if the filed square is parallel to surfaces “A”, “B”, “C” and “D”.
Metal Plate − Working Step No. 6
1. Mark two lines for the height of the letters and vertical lines for each letter. For the width let
approximately 1 mm clearance both sides.
2. Adjust the letter stamp on the surface of the work piece.
3. Strike the letter stamp using a 200 g hammer.
Metal Plate − Working Step No. 7
58
1. Lay out the lines for drilling using the measurement given.
2. Punch all the marks for drilling.
Metal Plate − Working Step No. 9
1. Drill the holes with required twist drills.
2. Countersink both sides of holes with countersink tool.
3. Tap the threads with required screw taps.
4. Check the specifications for holes “1” and “2” in the complete technical drawing of the
workpiece.
59
7. PRINCIPLES OF MECHANICAL METAL CUTTING
A large portion of manufacturing operations in the world consists of machining metal to size and shape. To
be competitive, it is important that machining operations be as cost−efficient as possible. This requires a good
knowledge of metals, cutting tools, and machining conditions and processes.
7.1 Classification of Metal Cutting Processes
Hand Cutting Processes
Machine Cutting Processes
• Filing
• Chiseling
• Hand Hacksawing
• Shearing
• Hand Tapping
• Die−Tapping
• Hand Reaming
• Drilling
• Hacksawing
• Turning
• Milling
• Grinding
• Shaping
• Machine Threading
• Machine Reaming
Chiseling
Sawing
Turning
Grinding
7.2 Angles of tools
• What is common to all cutting tools is the wedge shape BETA (?).
• To cut metals, the tool must be wedge−shaped, be resistant to abrasion and tenacious.
60
• For different cutting operations there is a need for different tool angles.
• Cutting tools with small wedge angles penetrate the material more easily but also tend to
break off more easily if the material is hard
Wedge Angle Beta (?):
The wedge angle must suit to the material being worked.
• The smaller the wedge angle is, the lower the expenditure of force.
• The harder the material, the larger the wedge angle should be chosen.
Clearance Angle Alpha (?):
The clearance angle is the angle between the flank of the tool and the surface being cut.
Friction and heating depend upon this angle. The angle should be chosen as such that the tool could cut
freely.
• Soft materials require a larger clearance angle because they generate more heat and
friction.
Rake Angle Gamma (?):
The rake angle is the angle between the cutting face and the plane of reference of the tool, an imaginary
surface perpendicular to the cut surface.
The rake angle influences the chip formation.
• Large angle: good chip flow, low cutting force
• Small to negative angle: great cutting force, highly robust cutters
61
7.3 Cutting Tool Guideline
• Cutting tools are expensive therefore take care of them.
• Always use sharp cutting tools to ensure an efficient cutting action and accurate work.
• Use the largest nose radius possible (Cold chisel, lathe tool….)
• Clamp the workpiece as short as possible and securely.
• Always use the speeds, feeds, and depth of cuts recommended by the manufacturer for the
material being cut and the cutting tool used.
• Use enough of the proper coolant for the material being cut and the cutting tool used.
8. DRILLING
8.1 Drill Press
A drill press is a machine used for drilling operations available in a wide variety of types and sizes to suit
different types and sizes of workpieces. The most common machine type found in a metal shop is the
floor−type drill press.
8.1.1 Drill Press Parts
Although drill presses are manufactured in a wide variety of sizes, all drilling machines contain certain basic
parts.
Base:
The base, usually made of cast iron, provides stability for the machine and rigid mounting for the column. The
base is usually provided with holes so that it may be bolted to a table or bench to keep it rigid. The slots or
ribs in the base allow the work−holding device for the workpiece to be clamped to the base.
Column:
The column is an accurate, vertical, cylindrical post that fits into the base. The table, which is fitted on the
column, may be adjusted to any point between the base and head. The head of the drill press is mounted
near the top of the column.
Table:
The table, either round or rectangular in shape, is used to support the workpiece to be machined. The table,
whose surface is at 90 degree to the column, may be raised, lowered, and swiveled around the column. On
some models it is possible to tilt and lock the table in either direction for drilling holes on an angle. Slots are
provided in most tables to allow jigs, fixtures, or large workpieces to be clamped directly to the table.
Drilling Head:
The head, mounted close to the top of the column, contains the mechanism to revolve the cutting tool and
advance into the workpiece. The spindle, which is a round shaft that holds and drives the cutting tool, is
housed in the spindle sleeve. The spindle sleeve does not resolve, but is moved up and down by the hand
feed lever that is connected to the pinion on the rack of the spindle sleeve. The end of the spindle may have a
tapered hole to hold taper shank tools, or it may be threaded or tapered for attaching a drill chuck.
The hand feed lever is used to control the vertical movement of the spindle sleeve and the cutting tool. A
depth stop, attached to the spindle sleeve, can be set to control the depth that a cutting tool enters the
workpiece.
62
Drill Chuck:
Drill chucks are the most common devices used on a drill press for holding straight−shank cutting tools. Most
drill chucks contain three jaws that move all at the time when the outer collar is turned. The three jaws hold
the straight shank of a cutting tool securely and cause it to run accurately.
8.1.2 Drill Sleeves and Sockets:
The size of the tapered hole in the drill press spindle is generally in proportion to the size of the machine: The
larger the machine, the larger the spindle hole. A drill sleeve is used to adapt the cutting tool shank to the
machine spindle if the taper on the cutting tool is smaller than the tapered hole in the spindle.
Before a taper shank tool is mounted in a drill press spindle, be sure that the external taper of the tool shank
and the internal taper of the spindle are thoroughly cleaned. Align the tang of the tool with the slot in the
spindle hole and, with a sharp upward snap, force the tool into the spindle.
63
Remove a taper shank tool:
A drift, a wedge−shaped tool, is used to remove a taper−shank tool from the drill press spindle. Place a piece
of wood under the tool. Insert the drift and sharply strike the end of it with hammer to remove the tool from the
drill press spindle.
8.2 Twist drill
A twist drill is a cutting−tool used to produce a hole in a piece of metal or other material. The most common
drill manufactured has two cutting edges (lips) and two straight or helical flutes.
The flutes provide the cutting edges with cutting fluid and allow the chips to escape during the drilling
operation.
Drill bit materials:
High−speed steels drills are the most commonly used drills, since they can be operated at good speeds and
the cutting edges can withstand heat and wear.
Cemented−carbide drills, which can be operated much faster than high−speed steel drills, are used to drill
hard materials. They can be operated at high speeds and they can withstand higher heat.
64
8.2.1 Twist drill parts and cutting angles
A twist drill may be divided into three main sections:
• Shank:
The shank is the part of the drill that fits into a holding device. It may be either straight
or tapered.
• Body:
The body contains the flutes, margin, and body clearance of the drill.
• Point:
Shape and condition of the point are very important to the cutting action of the drill.
Angles for General Purpose
Angles for Soft Material
65
Angles for Hard Material
Cutting angles of a twist drill
The parts of a twist drill point
8.2.2 Drill Sizes
Metric drills:
Metric drills are available in various set ranges.
Miniature set:
Sizes from 0.04 to 0.99 mm in steps of 0.01 mm
Straight shank:
Sizes from 0.5 to 20 mm in steps of 0.02 to 1 mm (depending on the size)
Taper shank:
Sizes from 8 to approx. 100 mm
Inch drills:
The most common system for inch drills is the fractional system.
Drills are available in sizes from 1/64 to 3 ½ in. in diameter, varying in steps of 1/64 in. from one size to the
next. Drills larger than 3 ½ in. in diameter must be ordered specially from the manufacturer.
66
8.2.3 Setting the Spindle Speed
To find the right number of revolutions per minute at which a drill press spindle will be set, the following
information must be known:
• The recommended cutting speed (CS) of the material to be drilled
• The type of drill bit, most likely HSS
• The diameter of the drill
Other important factors might affect the setting of the spindle speed:
• The type and the condition of the machine
• The accuracy and finish of the hole required
• The rigidity of work setup
• The use of cutting fluid
Calculating the spindle speed for Metric drills:
CS
= cutting speed of the material in meter per minute
D
= diameter of the drill in mm
?
= 3.1416
r/min = revolution per minute
Example:
Calculate the r/min. at which a drill press should be set to drill 12 mm hole in a piece of mild steel.
r/min = (CS × 1000) / (3,1416 × 12)
r/min = 30000 / 37.69
r/min = 796
Cutting speed for high−speed steel (HSS) drills
Material
Stainless Steel
Tool Steel
Cast Steel
Mild Steel
Aluminum & Brass
Cutting Speed (CS)
10 M/Min
15 M/Min
20 M/Min
30 M/Min
60 M/Min
Drill bit Ø in mm
67
Revolution per Minute (rpm/min)
2
1592
2387
3183
4775
9549
3
1061
1592
2122
3183
6366
4
796
1194
1592
2387
4775
5
637
955
1273
1910
3820
6
531
796
1061
1592
3183
7
455
682
909
1364
2728
8
398
597
796
1194
2387
9
354
531
707
1061
2122
10
318
477
637
955
1910
11
289
434
579
868
1736
12
265
398
531
796
1592
13
245
367
490
735
1469
14
227
341
455
682
1364
15
212
318
424
637
1273
20
159
239
318
477
955
25
127
191
255
382
764
Exercise Sheet − Calculating the spindle speed of Metric drills
CS
= cutting speed of the material in meter per minute
D
= diameter of the drill in mm
?
= 3.1416
r/min = revolution per minute
Exercise 1:
Calculate the r/min. at which a drill press should be set to drill a 10 mm hole in a piece of aluminum.
Exercise 2:
Calculate the r/min. at which a drill press should be set to drill a 22.5 mm hole in a piece of mild steel.
Exercise 3:
Calculate the r/min. at which a drill press should be set to drill a 5.8 mm hole in a piece of mild steel.
8.3 Different Drill Press Operations
68
Countersink Tool
Counterbore Tool
8.4 Facts and Problems
The most common drill problems encountered are illustrated below.
69
Excessive speed will cause
wear at outer corners of drill.
This leads to more regrinding
of material.
Excessive feed sets up
abnormal end thrust that
causes breakdown of chisel
point and cutting lips. Failure
included by this cause will be
broken or split drill.
Cutting with unequal angles
will cause one cutting edge to
work harder than the other.
This causes to poor tool life.
Cutting lips unequal in length
cause chisel point to be off
center with axis and will drill
holes oversize by appr. Twice
the amount of eccentricity.
8.5 Drill Press Safety
Safety Rules
• Never wear loose clothing around machinery
• A hair net or a cap must protect long hair to prevent it from becoming caught in the
revolving parts of the drill press.
• Never wear rings, watches, bracelets or necklaces while working in a machine shop.
• Always wear safety glasses when operating any machine.
• Never set the speed, adjust or measure the work until the machine is completely stopped.
• Keep the work area and floor clean and free of oil and grease.
• Never clamp taper shank drills, end mills, or non−standard tools in a drill chuck.
• Never leave a chuck key in a drill chuck at any time.
• Always use the brush to remove chips.
• Always clamp workpieces when drilling holes larger than ½ in. (12.7 mm) in diameter.
70
• When drilling sheet metal, it is necessary to clamp the sheet on a piece of wood.
• Reduce drilling pressure as the drill breaks through the workpiece.
• Always remove the burrs from a hole that has been drilled.
9. CUTTING THREADS WITH TAP & DIES
Whenever possible, threads should be cut with machines where they can be accurately controlled and the
thread cut will be of high quality. Sometimes it may be necessary, due to the size and shape of the workpiece,
or because only a few parts are required, to cut the thread with hand tools. Done with care, fairly accurate
internal threads can be cut with a tap; external threads can be cut with a die.
9.1 Main Parts of a Screw Thread
9.2 Hand Tapping
Hand Tap
A tap is a cutting tool used to cut internal threads. Normally its made of high−speed steel (HSS).
Hand taps are usually made in sets of three, because it is better to distribute all the cutting work during the
thread−process to three taps.
No. 1 (taper) tap:
1 ring on
shank
No. 2 (plug) tap:
2 rings on
shank
No. 3 (bottoming) tap:
without ring
The most common taps have two or three flutes in order to form the cutting edges, transport the chips out of
the hole and give way for the lubricant. The end of the tap is square so that a tap wrench can be used to turn
it into a hole.
71
Tap − Cutting Angles
Tap Wrenches Adjustable
Tap Wrenches Fixed
Tapping a Hole
Before a tap is used, a hole must be drilled in the workpiece to the correct tap drill size. The tap drill size
(T.D.S.) is the size of the drill that should be used to leave the proper amount of material in the hole for a tap
to cut threads. Then countersink both sides of the hole.
If there is no tap drill size chart available, the tap drill size can be easily found by applying simple formulas:
Inch Threads
T.D.S. = D in inch − 1/N
Metric Threads
T.D.S. = D in mm − P
72
T.D.S. = tap drill size
D = major diameter of tap
N = number of threads per inch
T.D.S = tap drill size
D = major diameter of tap
P = pitch
Table of Drill sizes
Metric
Pitch mm
Drill Ø mm
UNC
TPI
Drill Ø mm
UNF
TPI
Drill Ø mm
M3
0.50
2.5
1/4“
20
5.1
1/4“
28
5.5
M4
0.70
3.3
5/16”
18
6.6
5/16”
24
6.9
M5
0.80
4.2
3/8”
16
8.0
3/8”
24
8.5
M6
1.00
5.0
7/16”
14
9.4
7/16”
20
9.9
M8
1.25
6.8
1/2”
13
10.8
1/2”
20
11.5
M 10
1.50
8.5
9/16”
12
12.2
9/16”
18
12.9
M 12
1.75
10.2
5/8”
11
13.5
5/8”
18
14.5
M 16
2.00
14.0
3/4”
10
16.5
3/4”
16
17.5
M 20
2.50
17.5
7/8”
9
19.5
7/8”
14
20.4
M 24
3.00
21.0
1”
8
22.25
1”
12
23.25
Working Steps for Hand Tapping
1.
Step:
Select the correct size and type of tap for the job (blind hole or through hole).
2.
Step:
Select the correct tap wrench for the size being used.
3.
Step:
Use a suitable cutting fluid (No cutting fluid for brass or cast iron).
4.
Step:
Place the tap in the hole as near to vertical as possible.
5.
Step:
Apply equal down−pressure on both handles, and turn the tap clockwise (for right−hand thread) for
about two turns.
6.
Step:
Remove the tap wrench and check the tap for squareness. Check at two positions 90 degree to
each other.
7.
Step:
If the tap has not entered squarely, remove it from the hole and restart it by applying slight
pressure in the direction from which the tap leans. Be careful not to exert too much pressure in
the straightening process, otherwise the tap may be broken.
8.
Step:
Turn the tap clockwise one−half turn and then turn it backward about one−quarter of a turn to break
the chip. This must be done with a steady motion to avoid breaking the tap.
73
Turn clockwise with light pressure
Check the 90−degree Angle
9.3 Threading Dies
A threading die is used to cut external threads on round workpieces. The most common threading dies are the
adjustable and solid types. The round adjustable die is split on one side and can be adjusted to cut slightly
over or under−sized threads. It is mounted in a die stock, which has two handles for turning the dies onto the
work.
The solid die, cannot be adjusted and generally used for re−cutting damaged or oversized threads. Solid dies
are turned onto the thread with a special die−stock, or adjustable wrench.
Adjustable Die
74
Die Stock
Solid Die
Thread with a Hand Die − Working Steps
The threading process requires the machinist to work carefully to produce usable parts and avoid damage.
The following describes the procedure to be used.
1. Step:
Chamfer the end of the workpiece with a file or on the grinder. Consider that a 3/4” thread
requires a bolt with an outside diameter of 3/4”.
2. Step:
Fasten the workpiece securely in a vise. Hold small diameter work short to prevent it from
bending.
3. Step:
Select the proper die and die stock.
4. Step:
Lubricate the tapered end of the die with a suitable cutting lubricant.
5. Step:
Place the tapered end of the die squarely on the workpiece.
6. Step:
Apply down−pressure on both die−stock handles and turn clockwise several turns.
7. Step:
Check the die to see if it has started squarely with the work.
8. Step:
If it is not square, remove the die from the workpiece and restart it squarely, applying slight
pressure while the die is being turned.
9. Step:
75
Turn the die forward one turn, and then reverse it approximately one−half of a turn to break the
chip.
10.
Step:
Apply cutting fluid frequently during the threading process.
10. SHARPENING TOOLS
For some tools it is very important to keep them sharp at all times. Common tools, such as scribers, center
punchs, chisels, drill bits, tool bits for lathe machine needs to be sharpened every time you feel that they do
not cut well.
10.1 Bench Grinder or Pedestal Grinder
The bench grinder is used for the sharpening of cutting tools and the rough grinding of metal. Because the
work is usually held in the hand, this type of grinding is sometimes called “offhand grinding”.
The bench grinder is mounted on a bench while the pedestal grinder being a larger machine, is fastened to
the floor. Both types consist of an electric motor with a coarse abrasive grinding wheel for the fast removal
of metal, while the other is a fine abrasive wheel for finish grinding.
• The grinding wheels are normally made of Aluminum−Oxide or Silicon−Carbide.
Aluminum−Carbide is used to grind High−Tensile−Strength Materials. Silicon−Carbide is used
to grind Low−Tensile−Strength Materials.
• The wheel guards give the necessary protection while grinding
• The tool rest provide a rest for either the work or hands while grinding
• The eye shield is an additional protection for the eyes and should be used
Redressing the grinding wheels:
When a grinding wheel is used, several things can happen to it:
• Grooves become worn in the face of the wheel
• The abrasive grains will loose its cutting action
• Small metal particles imbed themselves in the wheel, causing it to become loaded or
clogged.
Use from time to time a disc type dresser or a dressing stone to remove the grooves and the metal particles.
This will also re−sharpen the abrasive grains.
76
10.2 Sharpening Tools
Sharpening Scriber and Center Punch
• Scriber and center punch should be ground in the position as shown beside.
• Use the tool rest to rest your hands while bringing the tool in the right position.
• Rotate the tool while grinding.
• Cool the tool down from time to time.
• Do not overheat the metal.
Sharpening Chisel
• Chisels should be ground in the position as shown below.
• Use the tool rest to rest your hands while bringing the tool in the right position.
• Use the whole grinding wheel while grinding. Move with the tool regularly from the left to the
right side and back.
• Cool the tool down from time to time.
• Do not overheat the metal.
• Grind the chisel−point parallel and straight. See also the pictures below.
77
10.3 Safety Precautions:
1. When switching on the machine, stand beside, because a damaged wheel might burst
during acceleration.
2. Always use safety goggles when grinding
3. The tool rest should never have more than 2−3 mm distance to the grinding wheel
4. Small workpieces should be held with clamps or other suitable devices
5. Keep the metal cool by dipping it frequently in water
6. Stand comfortable and don’t give to much force to the workpiece because in the case of
slip off with the workpiece you will grind your fingers or hand
7. While grinding, use only the face of the wheel
LIST OF NEEDED RESSOURCES FOR “GENERAL METAL” COURSE
Need to
Order/Replace/Organize
Resource
Checked Unit
Qty for 1
Trainee
Qty for 4
Trainees
Unit Qty
Unit
Price
Amount
Teaching Aids
Forms
78
Consumables and
Parts for Exercises
11. APPENDIX
APPENDIX NO. 1
Common Sizes for ordering Materials − Conversion Inch to Millimeter
1 millimeter
79
=
0.0394 inch
1 inch
=
25,4
millimeters
1 centimeter
=
0.3937 inch
1 inch
=
2.54
centimeters
1 meter
=
39.37 inches
1 foot
=
0.3048
meter
Inch
Millimeter
1/16
1.6
1/8
3
3/16
5
1/4
6
5/16
8
3/8
10
7/16
11
1/2
12
9/16
14
5/8
16
11/16
18
3/4
20
7/8
22
1
25
1 1/8
28
1 1/4
30
1 5/16
32
1 3/8
35
1 1/2
40
1 3/4
45
2
50
APPENDIX NO. 2
Sheet Metal Work
Materials used for sheet metal work
Material
Use
Technical Aspects
Appearance
Black Iron
• steel cabinets, machine
guards
• easy to cut, bent, form and
weld
• corrodes easily
• black dull or rusty
Galvanized
Iron
• car production, water
tank, gutters, air ducts
• resistant to corrosion
• bright spangled because
of the zinc coating
Tin Plate
• food containers
• expensive
• can be cut bent
• silvery mirror−like finish
80
Stainless
Steel
• kitchen equipment
• sink
• chemical industry
• resistant to corrosion
• resistant to many chemical
products
• easy to clean
• available with polished
surface
• silver chrome
Aluminum
• cooking utensils
• window & door frames
• airplane
• very light in comparison to
other metals
• available as an alloy to make
it harder and stronger
• pure aluminum is very soft
• whitish shiny
Copper
• gutter,
• kettle
• kitchen utensils
• easy to cut bent and solder
• High degree of workability
• reddish
Conversions table Gauge No. to Millimeter for Steel Sheet
The standard measurements of sheet metal are: 2,400 mm × 1,220 mm (8 ft. × 4 ft.), but there are also other
measurements available. Please check out with your hardware dealer.
Gauge No.
Equivalent in mm
Gauge No.
Equivalent in mm
32
0.25
20
0.91
31
0.27
19
1.06
30
0.30
18
1.21
29
0.34
17
1.37
28
0.38
16
1.52
27
0.42
15
1.71
26
0.45
14
1.90
25
0.53
13
2.28
24
0.61
12
2.66
23
0.68
11
3.04
22
0.76
10
3.42
21
0.84
GENERAL METAL WORK − FINAL TEST
Name: ……………
1.
Batch Nr. …..
Date: ……………
How can metals be classified in general?
1 point
a) Natural Products / Non Natural Products
b) Ferrous Steel / Nonferrous Steel
c) Cast Iron / Steel
d) Wrought Iron / Steel
2.
81
How can different metals be roughly identified?
1 point
a) By their appearance
b) By their temperature
c) By their elasticity
d) By their costs
3.
What is a typical use of Cast Iron?
1 point
a) Drill bits
b) Exhaust of a car
c) Roof of a house
d) Body or base of machines
4.
What is a typical use of Mild Steel?
1 point
a) Drill bits
b) Body of bench vise
c) Bolts, nuts or rivets
d) hacksaw blade
5.
Name two (2) physical properties and two (2) mechanical−technological properties of
metals
4
points
_________________________________________
_________________________________________
_________________________________________
_________________________________________
6.
Name three (3) common shapes of metals?
3
points
_________________________________________
_________________________________________
_________________________________________
7.
How do you order Angle bars at a hardware store? By the measurement of:
1 point
a) Thickness × Width × Length
b) Width × Height × Length
c) Diameter × Length
d) Schedule × Length
8.
How do you order Flat bar at a hardware store? By the measurement of:
1 point
82
a) Thickness × Width × Length
b) Width × Height × Length
c) By their Elasticity
d) By their costs
9.
When do you scale up a workpiece in technical drawing? For example S = 2:1
1 point
a) If it is made of wood
b) If the shape is round
c) If the workpiece is to small to show the details
d) If the workpiece is to big to fit on the paper
10. Write down the names of the given lines
4
points
a.
______
b.
______
c.
______
d.
______
11. What does Interchangeability means?
1 point
a) A worker can work all over the world
b) Parts produced within limits, can be used world wide
c) Aluminum in the Philippines has the same appearance than in Japan
d) Interchangeability is the relation between the Peso to the US$
12. What is the Maximum Limit for a bolt
20+0.05 mm?
1 point
a) 19.50 mm
b) 19.95 mm
c) 20.00 mm
d) 20.05 mm
13. What is the tolerance of a hole with this specification
a) 20.00 mm
b) 19.75 mm
c) 0.25 mm
83
20−0.25 mm?
1 point
d) 0.50 mm
14. Name three (3) common parts of a drill press
3
points
_________________________________________
_________________________________________
_________________________________________
15. Which of the following statements is true?
1 point
a) The harder the material, the smaller the wedge angle of a cutting tool
b) The softer the material, the bigger the wedge angle of a cutting tool
c) The softer the material, the smaller the wedge angle of a cutting tool
16. Name three (3) laying out tools
3
points
_________________________________________
_________________________________________
_________________________________________
17. Name three (3) common benchwork tools
3
points
_________________________________________
_________________________________________
_________________________________________
18. What can be adjusted on the arc−welding machine?
1 point
a) Watt
b) Voltage
c) Amperage
19. What is the common type of electrode used for arc welding?
1 point
a) Flux coated
b) Bare electrode
c) Square electrode
20. What is the common type of electrode used in welding mild steel using arc welding
technology?
1 point
84
a) 4711
b) 6013
c) 4080
21. Name three (4) common personal safety equipment used during welding operations
4
points
_________________________________________
_________________________________________
_________________________________________
_________________________________________
22. Which of the following statements is true?
1 point
a) The A drill point angle with 118 degree is good for general purpose
b) A drill point angle with 118 degree is good for soft metals
c) A drill point angle with 118 degree is good for hard metals
23. Which of the following statements is true?
1 point
a) Drilling hard metals needs a higher cutting speed
b) Drilling hard metals needs a lower cutting speed
c) Drilling soft metals needs a lower cutting speed
24. What is the recommended distance between tool rest and grinding wheel at a
benchgrinder?
1 point
a) 10 to 15 mm
b) 2 to 3 mm
c) 0.5 to 0.75 mm
25. Give the right measurement
85
2
points
Total score:
46 points
= 100%
Actual score:
…………
= ……..%
86