WORKSHOP TECHNOLOGY

eBook PSP | Workshop Technology 44

6.3 CNC Axis Conventions

a. The z-axis is parallel to the main spindle of the machine.
b. The x-axis is always horizontal to the table and at 90o to z.
c. The y-axis is at the other side. It right angles to both the x and z axes.

6.4 Programming Codes

a. G codes – call up machining commands
b. M codes – call up machine control activities
c. T codes – call up tool selection
d. F codes – call up feed rates
e. S codes – call up spindle speed

G Codes (Preparatory Codes)
Codes commonly used
GOO Rapid movement for position – commonly used
GOI Linear interpolation used for straight-line feed
G02 Circular interpolation, clockwise – commonly used
G03 Circular interpolation, counterclockwise – commonly used
G90 Absolute mode
G91 Incremental mode

M Codes (Control The Auxiliary Functions)
Codes commonly used
M02 End of program – commonly used
M03 Spindle on, clockwise – commonly used
M06 Tool change – commonly used

45 eBook PSP | Workshop Technology

6.5 Linear Interpolation

Under this command the machine tool will move in a straight line.
G01 → Move in a straight line

6.6 Circular Interpolation

G02 – Clockwise
G03 - Counterclockwise

6.7 Types Of Control System

There are two types of control systems.

a. point-to-point system
There are two types in point-to-point system which are absolute system and incremental
system.

b. continuous-path system.
The continuous-path system is more commonly known as the contouring system. The
contouring system has the capability of controlling its drive motors independently at
various speeds as the tool moves towards the specified position.

6.7.1 Absolute

a. The data in the absolute system describes the next location always in terms of its
relationship to the fixed zero point.
b. The zero point when used as a programmed datum is known as the programmed origin.
c. The G90 code sets the control up in absolute mode.
d. All moves are performed with respect to the axes zero.

eBook PSP | Workshop Technology 46

Example 1

Figure 6.2 Absolute Example 1

Example 2

Figure 6.3 Absolute Example 2

47 eBook PSP | Workshop Technology

Exercise 1

A block as shown below is to be machined, write a program in absolute mode in box below.

Figure 6.4 Absolute Exercise 1

eBook PSP | Workshop Technology 48

Exercise 2

A block as shown below is to be machined, write a program in absolute mode in box below.

Figure 6.5 Absolute Exercise 2

49 eBook PSP | Workshop Technology

Exercise 3

A block as shown below is to be machined, write a program in absolute mode in box below.

10 80 10
P5 P3 P4

30 30
P2 P5

30 30
P1
P6

10 80 10
Figure 6.6 Absolute Exercise 3

eBook PSP | Workshop Technology 50

6.7.2 Incremental

a. The word "incremental" may be defined as a direction or a movement with respect to
the preceding point in a prescribed sequence of points.
b. Each positioning move is described quantitatively in distance and in direction from a
previous points rather than from a fixed zero reference point.
c. In incremental mode all moves are with respect to the last position reached.

Example 1

Figure 6.7 Incremental Example 1

Example 2

Figure 6.8 Incremental Example 2

51 eBook PSP | Workshop Technology

Exercise 1

A block as shown below is to be machined, write a program in incremental mode in box
below.

Figure 6.9 Incremental Exercise 1

eBook PSP | Workshop Technology 52

Exercise 2

A block as shown below is to be machined, write a program in incremental mode in box
below.

Figure 6.10 Incremental Exercise 2

53 eBook PSP | Workshop Technology

Exercise 3

A block as shown below is to be machined, write a program in incremental mode in box

below.

181
000

P P4
3

3 3
0 0
P
P 5
2

33

0 0
P P
6
1

18 1
0 Figure 6.11 Increm0ental Exercise 3 0

eBook PSP | Workshop Technology 54

6.7.3 Continuous Path System

a. In a contouring system or continuous path system, the positioning and the operations are
both performed along controlled paths but at different velocities. The contouring system is
typically used on lathes, milling machines, grinders, welding machinery, and machining
centers.

Figure 6.12 Continuous Path System

6.8 Advantages Of Computer Numerical Control

a. The design can be edited.
b. Programmed in computer numerical control can easily changes into metric system
c. It is widely used in industry.
d. Increased flexibility
e. Greater accuracy
f. More versatility
g. Programmed are stored on the machine ready for use.
h. Programmed and data can be modified on the machine.

6.9 Disadvantages Of Computer Numerical Control

a. High machine cost
b. Complicated maintenance
c. Skill & training are required for programming and maintenance.
d. Parts are imported from aboard.
e. High tooling cost
f. Temperature, humidity & dust must be controlled.

7CHAPTER55 eBook PSP | Workshop Technology

WELDING

7.1 Introduction to Shield Metal Arc Welding (SMAW)

Shield metal arc welding (SMAW) or called arc welding is described as a joining process that
used a welding power supply to create an electric arc between an electrode and the base
metal to melt the metals at the welding point.

Figure 7.1 Arc Welding Circuit
The stick welding power source provides either alternating current (AC) or direct current (DC),
depending on the electrode being used. The best welding are usually using DC power sources.

7.1.1 Arc Welding Equipment

The basic components of an arc welding machine is consisting of:
a. Work cables
b. Electrode cables
c. Electrode Holder
d. Power supply
e. Electrode

eBook PSP | Workshop Technology 56

7.1.2 Types Of Arc Welding Machines

a. Direct current arc welding machine (DC)
b. Alternating current arc welding machine (AC)
c. Integrated AC / DC
d. Power driven direct current petrol/diesel
e. Electric motor driven direct current

7.1.3 Differentiate The Types Of Polarity

Arc welding machine that usually used is type 'rectifiers' because it has two options in current
flow which are:
a. Direct current straight polarity – (D.C.S. P.)
b. Direct Current Reverse Polarity – (D.C.R.P.)

Direct Current Straight Polarity – (D.C.S. P.)
In straight polarity, the negative source connected to the electrodes

Electrode cable

Power source Electrode
Workpiece cable Workpiece

Figure 7.2 Straight Polarity

Characteristics of polarity are:
a. Deep transparency
b. Liquidity electrode slower
c. A moderate speed

57 eBook PSP | Workshop Technology

Direct Current Reverse Polarity – (D.C.R.P.)
In reverse polarity, the positive source connected to the electrodes

Figure 7.2 Reverse polarity of direct current
Characteristics of polarity are:
a. Liquidity electrode faster.
b. Transparency in the shallow.
c. Speeds faster weld required.

7.1.4 Classify The Techniques Of Arc Welding

Angle of Welding Rod
a. 45 degrees of wedding rods in the direction of the right from the left
b. 90 degrees to two griddles.

Distance between the Welding Rod and Material
a. As a standard, the distance is about 3-5mm between electrode and workpiece.

Movements of Welding Rod
a. Weaving motion (uniform side-to-side motion) is applied to the electrode which gives

better fusion of the weld metal.
b. The motion of the rod must be uniform to get better weld.

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7.1.5 Welding Joints

a. Butt joint –
b. Edge joint –

c. Lapp joint –
d. Tee joint

e. Corner joint

Figure 7.4 Welding Joints

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7.1.6 Welding Positions

a. Flat
b. Horizontal (on a vertical plane).
c. Vertical
d. Overhead

7.1.7 Steps To Take Before Welding

Before you ever touch the welding machine there are a number of very important safety
checks that you should always make it a point to do first.
a. Safety – check the work area
b. Prepare necessary equipment - Safety glasses, welding mask, gloves, chipping hammer,

wire brush, apron and pliers
c. Prepare electrode
d. Select the suitable power supply and set the power.
e. Clean your metal
f. Set up your work-piece
g. Strike the workpiece
h. Start welding process.

7.1.8 Arc Welding Terminology Weld direction

Electrode Weld pool
Workpiece
Arc spray
Slag
Weld

Figure 7.5 Arc welding terminology

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7.1.9 Adjustment Of Electric Current

In the arc welding, the adjustment of an electric current is very important. If the electric
current is too low, the materials are not melted enough. If the electric current is too high, the
materials are melted excessively, and a hole is often made at the welding point.

7.1.10 Function of Slag / Flux

a. Protect the outside air during the molding of the cooling occurs.
b. Float the dirt to the surface of the molten crater.
c. Controlling the shape moldings so uniform.
d. Slowing down the cooling rate for repairing metal properties
e. Providing mechanical protection to the metal transfer from the electrode to the parent

metal.

7.1.11 Safety

a. Protective equipment – All the listed equipment protects you from heat, splatter and
harmful rays. (Ultraviolet & Infrared).

b. Gloves – leather
c. Do not hold hot metal or get them wet. Leather shrinks, burns and hardens.
d. Jacket – leather
e. Not to be used as a shop coat. For arc welding only.
f. Helmet – A full head and face shield
g. Protects head, face, and neck, can be adjusted and has a #10 welding lens.
h. Don’t Expose skin or eyes to a flash or arc.
i. Don’t try to chip slag without eye protection.

61 eBook PSP | Workshop Technology

7.2 Introduction to Oxy Acetylene Welding

Gas welding is a material joining process in which two or more parts are coalesced (joined
together) at their contacting surfaces by a suitable application of heat and/or pressure by
using mix of acetylene and oxygen gases. In some welding process a filler material is added
to facilitate coalescence.

7.2.1 Application Of Oxy-Acetylene

Gas welding is commonly used in industrial sector especially in metal fabrication work. Metal
sheets used usually from 1.0 mm to 3.0 mm in thickness.
For example general repair work- striking and patching the body of damage car.
Other general uses are:
a. Airplane Construction
b. Automobile Manufacture
c. Boiler Shops
d. Brass and Copper
e. Commercial welding
f. Electric Railway

7.2.2 Oxy-Acetylene Welding Equipment

a. Oxygen Cylinder
b. Acetylene Cylinder
c. Welding Torch / Welding Tip (Nozzle)
d. Pressure Regulators
e. Hose and Hose Fittings
f. Goggles and Face Shield
g. Gloves and Apron
h. Spark-Lighter
i. Filler Rod

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7.2.3 High Pressure And Low Pressure Oxy Acetylene Welding

a. Low pressure gas welding received acetylene supply from acetylene power plant with
pressure smaller than 1.0 psi or 1.0 bar

b. High pressure gas welding received acetylene supply from acetylene power plant with
pressure range 1 – 15 psi or 1 – 15 bar.

7.2.4 Regulators

A regulator reduces and controls the high pressure of gas from a cylinder to a constant lower
working pressure. Regulators used with oxygen and acetylene have two gauges. One gauge
shows cylinder pressure that may be used to indicate the amount of gas that remains in the
cylinder. The other provides a reading of line working pressure at the regulator.

There are two types of regulator used during oxy acetylene welding:
a. Single-stage regulator
b. Two-stage regulator

Pressure Regulator Function
a. Maintain a constant outlet pressure or flow.
b. Reduce the pressure in a system to a lower pressure or to regulate system pressure at

the desired value.

7.2.5 Welding Gases

Two types of gases commonly used is gas welding work are oxygen (O2) and acetylene (C2H2).
Combination of these two gases may produce the highest heat comparing to other gases. The
temperature may exceed 3316oC.

63 eBook PSP | Workshop Technology

Oxygen
Oxygen is colourless, odourless and tasteless gas at room temperature. Oxygen helps burning
and can react with metal and form oxidation on it. For example: Corrosion on steel
Acetylene Gas
Acetylene is a colourless hydrocarbon gas with a strong pungent odour or smell. It is made of
a composition of hydrogen and carbon. Acetylene is unstable gas and need to be keep
properly.

Oxy Acetylene Hoses
The oxygen hose is GREEN, and the acetylene hose is RED.

7.2.6 Welding Torch

There are two types of welding torches:
a. Injector Torch (cutting)
b. Equal-pressure Torch (welding)

7.2.7 Welding Tip

The tip is provided with a center hole through which a jet of pure oxygen passes. Mixed
oxygen and acetylene pass through holes surrounding the center holes for the preheating
flames. The tip must be kept clean

Figure 7.6 Diagram of oxy acetylene welding tip

eBook PSP | Workshop Technology 64

7.2.8 Welding Manifold System And Single Station System

Welding Manifold system is installed where welding operations are conducted in a fixed
location. Oxygen and acetylene are supplied to the welding stations through a pipe to each
welding stations. This arrangement produced comfortable and safe working place instead of
gas saver.

Figure 7.7 Manifold system
Single Station System – Oxygen and acetylene cylinder are combined together in each welding
stations. However this method use high quantity of gases and low safety precaution

Figure 7.8 Single station welding system

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7.2.9 Types Of Flames Used

a. The neutral flame - In which a balanced mixture of oxygen and acetylene is burned, is
used for welding operations.

b. The oxidizing flame -The oxidizing flame is produced by burning an excess of oxygen. It
used for cutting.

c. The carburizing flame -in which an excess of acetylene is burned, is used for brazing.

Figure 7.9 Types of Flames
Important of flame adjustment in gas welding
a. To ensure the ratio of acetylene and oxygen mixture suitable to the effects in welding

steel.
b. Reduce the influence to the weld pool.
c. As an adjustment of the heat requirement of welding job.

7.2.10 Advantages Of Oxy-Acetylene Welding

a. It's easy to learn.
b. The equipment is cheaper than most other types of welding rigs (e.g. TIG welding)
c. The equipment is more portable than most other types of welding rigs (e.g. TIG welding)
d. OA equipment can also be
e. used to "flame-cut" large pieces of material.

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7.2.11 Disadvantages Of Oxy-Acetylene Welding

a. OA weld lines are much rougher in appearance than other kinds of welds, and require
more finishing if neatness is required.

b. OA welds have large heat affected zones

7.3 Introduction to Metal Inert Gas (MIG)

Gas Metal Arc Welding (GMAW), also known as Metal Inert Gas (MIG) welding, is a joining
process that used a consumable wire electrode to produce the weld.

Arc welding Gas flow
power supply meter

Welding Spool of Inert gas
power electrode cylinder
cable wire

Electrode Contactor
feed rools lead,welding
current,electrode, and
inert gasto welding
gun

Contactor Control head
forelectrode
cable feed and gas
Ground supply

cable

Figure 7.10 MIG welding equipment

67 eBook PSP | Workshop Technology

Inert/noble
gas

Shielded
Arc gas

Melting

Work piece

Figure 7.11 MIG in progress

7.3.1 Shielding Gas

Table 7.1: Shielding gas

Metal Shielding Gas Remarks

Aluminium and Argon + helium High heat input
copper 20-80% mixture Minimum of porosity
Copper Argon + nitrogen Good heat input on copper
25-30% mixture
Carbon steels Argon + oxygen Stabilizes arc
Low alloy steels 3-5% mixture Reduces spatter
Causes weld metal to flow
Low alloy steels Mixture of argon, helium Eliminates undercut
and carbon dioxide May require electrode to contain
deoxidizers
Increases toughness of weld deposit

eBook PSP | Workshop Technology 68

7.3.2 Application

The process is suitable for welding aluminium, magnesium alloys, plain and low-alloy steels,
stainless and heat-resistant steel, copper and bronze, the variation being filler wire type of
gas shielding the arc.

7.3.3 Electrode

Electrodes used are much smaller in diameter than those used with the metal-arc process.
Sizes may range from 0.4 mm to 5.5 mm in diameter. Small diameter electrodes require high
feed rates, from 100 to 1,400 inches per minute.

7.3.4 MIG Welding Techniques

There are three methods of initiating the arc.
a. The gun switch operates the gas and water solenoids and when released the wire drive

is switched on together with the welding current.
b. The gun switch operates the gas and water solenoids and strikes the wire end on the

plate operates the wire drives and welding current (known as ‘scratch start’).
c. The gun switch operates the gas and water solenoids and wire feed with welding current

known as ‘scratch start’.

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7.3.5 Advantages Of MIG

a. Higher welding speeds
b. Greater deposition rates
c. Less post welding cleaning (e.g. no slag to chip off weld)
d. Better weld pool visibility
e. Highly versatile and one can work on a variety of materials
f. Low skill factor required to operate M.I.G
g. Easy to learn
h. Easy to operate
i. Very clean and efficient to use
j. High quality welding

7.3.6 Disadvantages Of MIG

a. Not suitable for outdoor welding work.
b. Need time to prepare the welding

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7.4 Introduction to Tungsten Inert Gas (TIG)

Gas tungsten arc welding (GTAW), also known as tungsten inert gas (TIG) welding, is a
welding process that used a non-consumable tungsten electrode to produce the weld. The
welding of aluminium and magnesium alloys by the oxy-acetylene and manual metal arc
processes is limited by the necessity to use a corrosive flux. The gas shielded, tungsten arc
process enables these metals and a wide range of ferrous alloys to be welded without the use
of a flux.

Torch

Power Gas
supply flow

Work
piece

Water
outlet

Figure 7.12 TIG welding equipment

Figure 7.13 TIG in progress

71 eBook PSP | Workshop Technology

7.4.1 Shielding Gas

Gas used with this process produces an atmosphere free from contamination and also
provides a path for arc transfer. The path creates an environment that helps stabilize the arc.
The gas and arc activity also perform a cleansing action on the base metal. Both argon and
helium are generally used for this process.

7.4.2 Filler Metal

Filler metals are selected to meet or exceed the tensile strength, ductility, and corrosion resis-
tance of the base metal. The usual practice is to select a filler metal having a composition
similar to that of the base metal. For most efficient application, select clean filler metals of
proper diameter; the larger the diameter of the filler metal, the more heat is lost from the
weld pool.

7.4.3 Advantages Of TIG

a. It produces a more precise weld
b. Can be used at lower amperages for thinner metal
c. Can be used on exotic metals.
d. TIG welding is a commonly used high quality welding process
e. High quality and strong welding finish
f. No flux
g. Most efficient ways to join two metals.

eBook PSP | Workshop Technology 72

7.4.4 Disadvantages Of TIG

a. Highly skilled needed
b. Take a lot of time when welding
c. High cost
d. Lower filler deposition rate as well.
e. Only weld thin materials

7.5 Weld Defects And Its Prevention

The properties of a welded joint depend on a few factors. There are
a. Metal should be cleaned.
b. Suitable size of welding tip and it cleanliness.
c. The speed of welding should be in stable condition
d. Suitable pressure for oxygen and acetylene
e. Angle of welding torch during welding
f. Form & thickness of metal to be weld
g. Pre-heat distance to the base metal

7.6 The Types Of Weld Defects

Type of defect in a gas welding
a. Lack of penetration
b. Lack of fusion
c. Poor appearance
d. Under cut
e. Porosity
f. Crack in weld

73 eBook PSP | Workshop Technology

Lack of penetration
Causes of defects
a. face and source distance is too thick
b. 'v' angle is too narrow
c. blowpipe nozzle holes are too narrow
d. welding speed is too fast
e. the distance between the metal and nozzle tip too far

How to overcome
a. face and source distance must be between 1.5mm - 2.0mm
b. 'v' angle should be between 60-70 degrees
c. medium speed of welding
d. the distance between the metal blowpipe nozzle is 2-3m

Lack of fusion
Causes of defects
a. Blowpipe nozzle holes are too narrow
b. Incorrect angle blowgun
c. Travelling too fast welding
d. The filler rod is too big
e. Rod is withdrawn before the molten metal

How to overcome
a. Use the correct torch tip according to the thickness of the metal
b. Welding angle is between 60o-70 o, while the filler rod angle is 30o-40o
c. Suitable welding speed
d. Using the suitable filler rod ( depends on base metal thickness)
e. Basic metals melted first and followed by filler rod in the middle of puddle

eBook PSP | Workshop Technology 74

Poor Appearance
Causes of defects
a. Welding speed is too fast
b. Torch distance is not stable
c. Incorrect flame adjustment
d. Base metal is not properly heated
e. Base metal surface is not clean

How to overcome
a. Welding speed must be appropriate
b. Blowgun nozzle distance to the base metal should be between 2-3mm
c. Adjust the flame according to the metal to be welded
d. Use the tip hole according to the thickness of the metal
e. Clean the metal surfaces

Undercut
Causes of defects
a. Incorrect welding angle
b. Base metal is too hot
c. Welded sling is too big and wide
d. Excessive heat
e. Incorrect movement of filler rod and torch

How to overcome
a. Proper welding angles between 60-70 degrees
b. Cooling the base metal first
c. Control the flame, to get the correct size of puddle
d. Pore size should be according to the thickness of the metal blowpipe
e. Stabilize the movement of welding and filler rod

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Porosity
Causes of defects
a. Metal surface is not clean
b. Inner touch the molten part
c. Incorrect flame adjustment
d. Excessive heat

How to overcome
a. Clean metal surfaces
b. Do not touch the place to weld when welding
c. Control the distance between the torch nozzle and the work piece
d. Adjust the flame base to metal (work piece) used
e. Use the correct size of the blowpipe, in accordance with the thickness of the metal

Cracks in Weld
Causes of defects
a. Improper pre-joint of work piece
b. Insufficient pre-heat
c. Disability due to other defects

How to overcome
a. pre-joint work piece must be correct in terms of diverted angle, distance and other

sources
b. proper pre-heat of the metal before welding
c. Fix the defects found in the previous welding before re-weld again.

eBook PSP | Workshop Technology 76

Summary

This Workshop Technology ebook aims at imparting knowledge and skill components in the
field of basic workshop technology. It deals with different hand and machine tools required
for manufacturing simple metal components and articles. It is hoped that this ebook This will
greatly benefit students, lecturers and even practicing engineers.

vii eBook PSP | Workshop Technology

References

Centre Lathe turning. Romeoengineering. (n.d.). Retrieved November 18, 2021, from
https://romeoengineering.com.au/centre-lathe-turning/.

Designed And Promoted By Maharashtra Industries Directory, W. (n.d.).
M.S.Enterprises. Metal Working Machines, Workshop Machines, Supplier, Pune,
india. Retrieved November 18, 2021, from https://workshopmachinery.com/.

Garg, S. K. (2005). Comprehensive workshop technology: Manufacturing processes.
Laxmi Publications.

Gas welding - oxyacetylene. (n.d.). Retrieved November 18, 2021, from
http://www.technologystudent.com/equip_flsh/acet1.html.

Griffin, V. (2017, July 14). Centre lathe. - PPT video online download. SlidePlayer.
Retrieved November 18, 2021, from https://slideplayer.com/slide/5766879/.

Hipatmachinetools. (2013, January 16). Important workshop machinery – lathe,
milling machine, press brake, Bandsaw Machines. Machine Tools – Lathe Machine
| Drilling Machine | Milling Machine | Shaping Machine | Grinding Machine.
Retrieved November 18, 2021, from
https://hipatmachinetools.wordpress.com/2013/01/16/important-workshop-
machinery-lathe-milling-machine-press-brake-bandsaw-machines-2/.

James, C. W. A. (1972). Workshop technology. Edward Arnold.

Nice, K. (2021, October 12). How gears work. HowStuffWorks Science. Retrieved
November 18, 2021, from http://science.howstuffworks.com/transport/engines-
equipment/gear.htm.

eBook PSP | Workshop Technology viii

Stasterisk, & Instructables. (2017, November 11). How to Weld - Tig Welding.
Instructables. Retrieved November 18, 2021, from
http://www.instructables.com/id/How-to-Weld-TIG/.

Scribd. (n.d.). Discover numerical control books. Scribd. Retrieved November 18,
2021, from https://www.scribd.com/interest/Numerical-Control/explore.

What does CNC mean? (n.d.). Retrieved November 18, 2021, from
http://www.technologystudent.com/cam/cnccut1.html.

Wikimedia Foundation. (2021, November 12). Numerical control. Wikipedia. Retrieved
November 18, 2021, from http://en.wikipedia.org/wiki/Numerical_control.

Wikimedia Foundation. (2021, November 15). Milling (machining). Wikipedia.
Retrieved November 18, 2021, from
http://en.wikipedia.org/wiki/Milling_%28machining%29.

Wikimedia Foundation. (2021, November 9). Oxy-fuel welding and cutting. Wikipedia.
Retrieved November 18, 2021, from http://en.wikipedia.org/wiki/Oxy-
fuel_welding_and_cutting.

Wikimedia Foundation. (2021, October 16). Gear. Wikipedia. Retrieved November 18,
2021, from http://en.wikipedia.org/wiki/Gear.

Workshop safety rules. (n.d.). Retrieved November 18, 2021, from
http://www.technologystudent.com/health1/safetyr1.htm.

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