This document provides lecture notes on workshop practice II, covering drilling operations and welding processes. It discusses drilling machine types, drilling geometry, cutting conditions, feed and speed, operations like drilling and reaming. It also covers welding principles like fusion and pressure welding, classification into oxy-acetylene, shielded metal arc, MIG and TIG welding. Key details are provided on welding processes, inert gas shielding, and consumable electrodes.

1. WORKSHOP PRACTICE II
LECTURE NOTES
BY
Jean de Dieu IYAKAREMYE (Msc)
Email: iyakjdd@gmail.com
University of Rwanda

2. AGM 204 WORKSHOP PRACTICE AND
APPLICATIONS
• Component Name: Workshop Practice II
Part 1: Drilling operation
Part 2: Welding Processes
Part 3: Lathe machine

3. Workshop Practice II
Part I. Drilling operation

4. 1. Introduction
• Drilling is a process of producing round holes
in a solid material or enlarging existing holes
with the use of multi-tooth cutting tools called
drills or drill bits.
• The hole is produced by axially feeding the
rotating drill into the workpiece which is held
on the table of the drilling machine.
• The most common widely employed drilling
tool is the twist drill.

5. 2. Types of holes
• Drilled holes can be either through holes or
blind holes (see Figure 1 on the next slide).
• A through holes is made when a drill exits the
opposite side of the work; in blind hole the
drill does not exit on the other side of the
workpiece.

6. • Two types of holes: (a) through hole and (b) blind
hole

7. 3. Drilling machines - Drill press

8. 3.1. Types of Drilling Machines
• The sensitive or bench drill is used for light
drilling on small parts.
• The upright drill press is used for heavy duty
drilling and finally the radial drill press is used
for drilling large, heavy work piece that are
difficult to move.

9. • Sensitive or Bench drill
press
• Upright drill press

10. Radial drill Press
• This is the largest drill
press designed to drill
up to 100-mm diameter
holes in large
workparts.
• It has a radial arm along
which the drilling head
can be moved and
clamped.

11. Other drilling machines
• The gang drill is a drill press consisting of a series
of drill presses connected together in an in-line
arrangement so that a series of drilling
operations can be done in sequence.
• In the multiple-spindle drill, several drill spindles
are connected together to drill multiple holes
simultaneously into the workpart.
• Numerical control drill presses (CNC)are available
to control the positioning of the holes in the
workparts.

12. 4. Geometry of twist drill
• The twist drill is the most used cutting tools in
the drilling operation.
Figure : Standard geometry of a twist drill

13. • The twist drill is the most used cutting tools in
the drilling operation.
• The twist drill is provided with two spiral grooves
and two cutting edges.
• The chips produced are guided up through these
spiral grooves.
• The grooves also serve as passage to the cutting
fluid.
• In order that the cutting edges can cut off chips,
two movements are required simultaneously;
rotational speed and axial feed.

14. • The typical helix angle of a general purpose twist drill is
18~30o
while the point angle (which equals two times
the major cutting edge angle) for the same drill is 118o
.
• Some standard drill types are,
 straight shank: this type has a cylindrical shank and is
held in a chuck;
 taper shank: his type is held directly in the drilling
machine spindle.
• Drills are normally made of HSS but carbide-tipped
drills, and drills with mechanically attached carbide
inserts are commonly used in many operations,
especially on CNC drilling machines.

15. Cutting Drill angles
• In twist drill, there are various angles to be considered:
 Cutting angle (ca) or angle of lip:
The two lips must be of same length and equal angle.
For ordinary work, the cutting angle is 59º and vary
with metal to metal.
 Lip clearance angle:
The cone shaped cutting end is the point from the lips
and varies from 12- 15º degrees. In drilling soft
materials, the angle may be increased under heavy
feeds. For hard materials, the recommended angle is
9º degrees. If reduced further the drill cannot cut into
the metal and may break in the centre along the web.

16. Rake angle: It is the angle between the flute
and the workpiece that is usually 70-75º
degrees. This helps to secure the lip over the
correct space to curl the chips. If more there
will be no edge for cutting and if less the
cutting edge will be too thin and may break
under strain.

17. 5. Cutting conditions in drilling
• The twist drill is a
cutting tool with two
symmetrical opposite
cutting edges, each
removing part of the
material in the form of
chip.
• Fig. : Basics of a drilling
operation.

18. 6. Motions of Drill and Cutting
Velocity
• In drilling, the primary motion is the rotation
of the cutting tool held in the spindle.
• Drills execute also the secondary feed motion.
• Cutting velocity V in drilling is not a constant
along the major cutting edge as opposed to
the other machining operations.
It is zero at the center of the twist drill, and
has a maximum value at the drill corner.
The maximum cutting speed is given by:

19. V = πDN
where D is the drill diameter, and N is the
rotational speed of the drill.
• As in the case of turning and milling, cutting
speed V is first calculated or selected from
appropriate reference sources, and then the
rotational speed of the drill N, which is used to
adjust drill press controls, is calculated.

20. 7. Feed in Drilling
• Feed (f) is the distance that the drill penetrates
per revolution (mm/rev), the share of each
cutting edge is = f/2
• Two types of feed in drilling can be identified:
feed per tooth fz: has the same meaning as in the
other multi-tooth cutting tools.
Feeds per tooth are roughly proportional to drill
diameter, higher feeds for larger diameter drills.
• feed per minute fm: feed per minute is calculated
taking into account the rotational speed N,
fm = 2fzN

21. • Feed per minute is used to adjust the feed change
gears.
• Depth of cut d is equal to the half of drill diameter,
d = 1⁄2 D
where D is the drill diameter.
• In core drilling, a drilling operation used to enlarge an
existing hole of diameter D(hole), depth of cut is given
by
d = 1⁄2 (D(drill) – D(hole))
where D(drill) is the drill diameter, and D(hole) is the
diameter of the hole being enlarged.

22. 8. Drilling time
• Drilling time (T) can be given by the equation;
T = L / f N;
Where f is the feed (mm/rev) N is the
rotational speed (rpm) L is the sum of hole
depth, approach and over travel distances.
*The approach is usually considered as 0.4D
while over travel ranges from 1 to 3mm.

23. 9. Drilling operations

24. • Drilling is used to drill a round blind or through
hole in a solid material. If the hole is larger than
~30 mm, its a good idea to drill a smaller pilot
hole before core drilling the final one. For holes
larger than ~50 mm, three-step drilling is
recomended;
• Core drilling is used to increase the diameter of
an existing hole.
• Step drilling is used to drill a stepped (multi-
diameter) hole in a solid material.

25. • Counterboring provides a stepped hole again but
with flat and perpendicular relative to hole axis
face. The hole is used to seat internal hexagonal
bolt heads.
• Countersinking is similar to counterboring,
except that the step is conical for flat head
screws.
• Reaming provides a better tolerance and surface
finish to an initially drilled hole. Reaming slightly
increases the hole diameter. The tool is called
reamer;

26. • Center drilling is used to drill a starting hole to
precisely define the location for subsequent drilling.
The tool is called center drill. A center drill has a thick
shaft and very short flutes. It is therefore very stiff and
will not walk as the hole is getting started.
• Gun drilling is a specific operation to drill holes with
very large length-to-diameter ratio up to L/D ~300.
There are several modifications of this operation but in
all cases cutting fluid is delivered directly to the cutting
zone internally through the drill to cool and lubricate
the cutting edges, and to remove the chips

27. 10. Reamers
• The reamer used in reaming operation has
similar geometry as for twist drill .
• The difference in geometry between a reamer
and a twist drill are:
The reamer contains four to eight straight or
helical flutes, respectively cutting edges.
The tip is very short and does not contain any
cutting edges.

29. 11. Drill materials
• Drills are normally made of high-speed steel
(HSS) but carbide-tipped drills, and drills with
mechanically attached carbide inserts are
commonly used in many operations, especially
on CNC drilling machines

30. 12. Apparatus needed during drilling
operation
• Normally, holes produced by drilling are bigger than the drill diameter and
depending on its applications; the drilled holes will subjected to other
operations such as reaming or honing to better surface finish and
dimensional accuracy
• There are also several apparatus needed during the drilling operation as
shown below:
 Drilling machine
 Center punch
 Hammer
 Center drill
 Twist drills
 Coolant
 Vernier caliper
 Two flute drill set: i. Center drill; ii. Countersink drill; iii. Counter bore drill;
iv. Drill various diameter

31. Part II. Welding Processes

32. Welding Processes
Ship Structures

33. 1. INTRODUCTION
• Welding is the process of permanently joining two or more metal
parts, by melting both materials. The molten materials quickly cool,
and the two metals are permanently bonded.
• Modern welding technology started just before the end of the 19th
century with the development of methods for generating high
temperature in localized zones.
• Welding generally requires a heat source to produce a high
temperature zone to melt the material, though it is possible to weld
two metal pieces without much increase in temperature.
• Welding process can be done with or without the application of
pressure, and with or without the use of filler metal.

34. 2. Classification of Welding
• Fusion Welding or Non-Pressure Welding
 The materials at the joint are heated to a molten
state and allowed to solidify.
(Ex) Gas welding, Electric Arc welding
• Pressure Welding or Plastic Welding
 The piece of metal to be joined are heated to a
plastic state and forced together by external
pressure.
(Ex) Resistance welding

35. Classification of Welding (Cont’)
Fusion Welding Pressure Welding
Homogeneous Heterogeneous
Brazing SolderingGas Welding
Electroslag
High Energy Beam
Electric Arc
MIG
TIG
Shielded Metal Arc – “Stick”
Friction Welding

36. 2.1. Fusion Welding Principles
• Base metal is melted
• Filler metal may be added
• Heat is supplied by various means
– Oxyacetylene gas
– Electric Arc
– Plasma Arc
– Laser

37. Fusion Weld Zone
Fig : Characteristics of a
typical fusion weld zone
in oxyfuel gas and arc
welding.

38. Fusion Welding
BASE METAL
WELD
SOLIDIFIED SLAG
ARC POOL
WELDING ATMOSPHERE
CORE WIRE
ELECTRODE COATING
ARC STREAM
PENETRATION
DEPTH

39. Weld Metal Protection
• During fusion welding, the molten metal in the weld
“puddle” is susceptible to oxidation
• Must protect weld puddle (arc pool) from the
atmosphere
• Methods
– Weld Fluxes
– Inert Gases
– Vacuum

40. Weld Fluxes
• Typical fluxes
– SiO2, TiO2, FeO, MgO, Al2O3
• Produces a gaseous shield to prevent
contamination the oxygen and nitrogen of
the air.
• Act as scavengers to reduce oxides.
• Add alloying elements to the weld.
• Influence shape of weld bead during
solidification.

41. Inert Gases
• Argon, helium, nitrogen, and carbon dioxide
• Form a protective envelope around the weld
area
• Used in
– MIG
– TIG
– Shield Metal Arc

42. Vacuum
• Produce high-quality welds
• Used in electron beam welding
• Nuclear/special metal applications
– Zr, Hf, Ti
• Reduces impurities by a factor of 20 versus
other methods
• Expensive and time-consuming

43. 3. Types of Fusion Welding
• Oxyacetylene Cutting/Welding
• Shielded Metal Arc (“Stick”)
• Metal Inert Gas (MIG)
• Tungsten Inert Gas (TIG)

44. 3.1. Oxy-acetylene Arc Welding
• Flame formed by burning a mix of acetylene (C2H2)
and oxygen
• Fusion of metal is achieved by passing the inner
cone of the flame over the metal
• Oxyacetylene can also be used for cutting metals
Inner Cone: 5000-6300 deg F Combustion Envelope 3800 deg F
2300 deg FTORCH TIP

45. Oxyacetylene flames
Fig : Three basic types of oxyacetylene flames used in oxyfuel-gas welding and
cutting operations: (a) neutral flame; (b) oxidizing flame; (c) carburizing, or reducing
flame. The gas mixture in (a) is basically equal volumes of oxygen and acetylene.

46. Oxyacetylene flames
• Oxygen is turned on, flame immediately changes into a long white inner area
(Feather) surrounded by a transparent blue envelope is called Carburizing flame
(30000
C)
• Addition of little more oxygen give a bright whitish cone surrounded by the
transparent blue envelope is called Neutral flame (It has a balance of fuel gas and
oxygen) (32000
c)
 Used for welding steels, aluminium, copper and cast iron
• If more oxygen is added, the cone becomes darker and more pointed, while the
envelope becomes shorter and more fierce is called Oxidizing flame
 Has the highest temperature about 34000
C
 Used for welding brass and brazing operation

47. Oxyacetylene Torch
Fig. (a) General view of and (b) cross-
section of a torch used in
oxyacetylene welding. The acetylene
valve is opened first; the gas is lit
with a spark lighter or a pilot light;
then the oxygen valve is opened and
the flame adjusted. (c) Basic
equipment used in oxyfuel-gas
welding. To ensure correct
connections, all threads on acetylene
fittings are left-handed, whereas
those for oxygen are right-handed.
Oxygen regulators are usually
painted green, and acetylene
regulators red.

48. 3.2. Shielded Metal Arc (Stick)
• An electric arc is generated between a coated
electrode and the parent metal
• The coated electrode carries the electric current to
form the arc, produces a gas to control the
atmosphere and provides filler metal for the weld
bead
• Electric current may be AC or DC. If the current is
DC, the polarity will affect the weld size and
application

49. Shielded Metal Arc (Stick)
Fig. Schematic illustration of the shielded
metal-arc welding process. About 50% of
all large-scale industrial welding operations
use this process.

50. Shielded Metal Arc (con’t)
• Process:
– Intense heat at the arc melts the tip of the electrode
– Tiny drops of metal enter the arc stream and are
deposited on the parent metal
– As molten metal is deposited, a slag forms over the bead
which serves as an insulation against air contaminants
during cooling
– After a weld ‘pass’ is allowed the cool, the oxide layer is
removed by a chipping hammer and then cleaned with a
wirebrush before the next pass.

51. 3.3. Inert Gas Welding
• For materials such as Al and its alloys or Ti
which quickly form oxide layers. The
shielded gases used are:
Argon, Helium, nitrogen, carbon dioxide or
mixture of them.
Argon and Helium are completely inert and
therefore they provide a complete inert
atmosphere around the puddle.

52. • Uses a consumable electrode (filler wire made of the base metal) and is
fed automatically from a coil into the arc.
• Inert gas is typically Argon
Metal Inert Gas (MIG)
BASE METAL PUDDLE
POWER
SOURCE
DRIVE WHEELS
CONSUMABLE
ELECTRODE
ARC COLUMNSHIELDING GAS

53. • Tungsten electrode acts as a cathode
• A plasma is produced between the tungsten cathode and the base
metal which heats the base metal to its melting point
• Filler metal can be added to the weld pool
Tungsten Inert Gas (TIG)
BASE METAL PUDDLE
POWER
SOURCE
ARC COLUMNSHIELDING GAS
TUNGSTEN
ELECTRODE
+ +
BASE METAL (ANODE)
TUNGSTEN
ELECTRODE
(CATHODE)
- - -
+ +

54. 4. Submerged arc welding
Fig : Schematic illustration of the submerged-arc welding process
and equipment. The unfused flux is recovered and reused .

55. Submerged arc welding (Cont)
Fig : Simplified schematic illustration of the submerged-arc welding
process

56. Submerged arc welding (Cont)
• Submerged arc welding (SAW) is an electric arc welding
process that uses a continuous, consumable bare wire
electrode.
• The arc shielding is provided by a cover of granular flux.
• The electrode wire is fed automatically from a coil into the
arc.
• The flux is introduced into the joint slightly ahead of the weld
arc by gravity from a hopper.

57. 5. Flux cored Arc Welding
• Flux cored arc welding (FCAW) is similar to a
gas metal arc welding (MIG).
• Electrode is tubular in shape and is filled
with flux.
• Cored electrodes produce more stable arc,
improve weld contour and produce better
mechanical properties.
• Flux is more flexible than others.

58. Equipment used in MIG and FCAW
Welding Operations
Fig : Basic equipment used in gas metal-arc (MIG) and (FCAW)
welding operations

59. 6. Plasma-Arc Welding Process
• Plasma Arc Welding (PAW) is a special form of gas
tungsten arc welding in which a plasma arc is directed at
the weld area.
• The tungsten electrode is contained in a specially
designed nozzle that focuses a high-velocity stream of
inert gas (for example, argon or argon-hydrogen mixtures,
and helium) into the region of the arc to produce a high-
velocity plasma jet of small diameter and very high-energy
density.
• Temperatures in plasma arc welding reach 30,000o C or
greater, hot enough to melt any known metal.

60. Plasma-Arc Welding Process (Cont)
Fig.: Two types of plasma-arc welding processes: (a) transferred, (b)
nontransferred. Deep and narrow welds can be made by this
process at high welding speeds.

61. 7.Welding Positions

62. 8.Main Joint Design
BUTT JOINTBUTT JOINT
STRAP JOINT
LAP JOINT
FILLET JOINT
CORNER JOINT

63. Derived Welding Joint Design
Fig. Examples of welded
joints and their
terminology.

64. 9. Resistance welding
• Resistance welding (RW) is a group of fusion
welding processes that utilizes a combination of
heat and pressure to accomplish coalescence.
• The heat required is generated by electrical
resistance to current flow at the interface of two
parts to be welded.
• The resistance welding processes of most
commercial importance are spot and seam
welding.

65. 9.1. Resistance Spot Welding
• Resistance spot welding (RSW) is a resistance
welding process in which fusion of the base metal is
achieved at one location by opposing electrodes.
• Resistance spot welding is widely used in mass
production of automobiles, appliances, metal
furniture, and other products made of sheet metal of
thickness 3 mm or less.

66. • The cycle in a spot welding operation consists of
the steps depicted in the figure:
Steps in a spot welding cycle: (1) parts inserted between open electrodes, (2)
electrodes close and force is applied, (3) weld time (current is switched), (4)
current is turned off but force is maintained, and (5) electrodes are opened,
and the welded assembly is removed.

67. 9.2. Resistance Seam Welding
• In Resistance Seam
Welding (RSEW), the
electrodes are two
rotating wheels as
shown in the figure:

68. Different types of seam welding
Different types of seam welding, (from left to right)
conventional seam welding, roll spot welding, continuous
resistance seam welding.

69. Different types of seam welding
(Cont’)
• The spacing between the weld nuggets in resistance seam
welding depends on the motion of the electrode wheels
relative to the application of the weld current.
• In the usual method of operation, called continuous motion
welding, the wheel is rotated continuously at a constant
velocity, and current is turned on at timing intervals
consistent with the desired spacing between spot welds along
the seam so that overlapping weld spots are produced.

70. Different types of seam welding
(Cont’)
• But if the frequency of current switching is reduced
sufficiently, there will be spacing between the weld
spots, and this method is termed roll spot welding.
• In another variation, the welding current remains on
at a constant level so that a truly continuous welding
seam is produced.

71. 10. Generalized Welding Symbol
FAR SIDE DETAILS
ARROW SIDE DETAILS
Field weld symbol
Weld all-around for
pipes, etc.
L1-L2
L1-L2
D = Weld Depth (usually equal to plate thickness)
L1 = Weld Length
L2 = Distance between centers for stitched welds
The Field Weld Symbol (generally used in arc welding)is a guide for installation.
Shipyards normally do not use it, except in modular construction.
Electrode
Material
D
D
Weld Geometry

72. Example Welding Symbol
1/2” 1/2”
1/2
1/2
One-sided welds are max 80% efficient
Two sided are 100% efficient
Geometry symbol for V-groove

73. Weld Symbols (Butt Joints)
Backing

74. Weld Symbol (Fillet Joints)

75. Weld Symbol (Corner Joints)

76. General Design Guidelines

77. 11. Electrode Designations

78. Weld Quality and Testing
in Arc Welding

79. 1. WELD QUALITY
• Welding discontinuities can be caused by inadequate or
careless application.
• The major discontinuities that affect weld quality are:
 Porosity
 Slag Inclusions
 Incomplete fusion and penetration
 Weld profile
 Lamellar tears
 Cracks
 Surface damage
 Residual stresses

80. Discontinuities and Defects in
Fusion Welds
Fig.1. Examples of various discontinuities in fusion
welds.

81. Fig.2. Schematic illustration of various defects in fusion welds.

82. 1.1. Porosity
• Caused by gases released during melting of the weld area but
trapped during solidification, chemical reactions,
Contaminants
• They are in form of spheres or elongated pockets.
• Porosity can be reduced by
 Proper selection of electrodes
 Improved welding techniques
 Proper cleaning and prevention of contaminants
 Reduced welding speeds

83. 1.2. Slag Inclusions
• Compounds such as oxides ,fluxes, and electrode-
coating materials that are trapped in the weld Zone.
• Prevention can be done by following practices :
 Cleaning the weld bed surface before the next layer
is deposited.
 Providing enough shielding gas.
 Redesigning the joint.

84. 1.3. Incomplete Fusion and
Penetration
• Produces lack of weld beads
• Practices for better weld :
 Raising the temperature of the base metal.
 Cleaning the weld area, prior to the welding.
 Changing the joint design and type of electrode.
 Providing enough shielding gas.

85. 1.4. Penetration
• Incomplete penetration occurs when the depth of
the welded joint is insufficient.
• Penetration can be improved by the following
practices :
 Increasing the heat Input.
 Reducing the travel speed during the welding.
 Changing the joint design.
 Ensuring the surfaces to be joined fit properly.

86. 1.5. Weld Profile
• Under filling results when the joint is not filed with
the proper amount of weld metal.
• Undercutting results from the melting away of the
base metal and consequent generation of a groove in
the shape of a sharp recess or notch.
• Overlap is a surface discontinuity usually caused by
poor welding practice and by the selection of
improper material.

87. 1.6. Cracks
• Cracks occur in various directions and various
locations
• Factors causing cracks:
 Temperature gradients that cause thermal
stresses in the weld zone.
 Variations in the composition of the weld zone.
 Embrittlement of grain boundaries
 Inability of the weld metal to contract during
cooling.

88. Types of cracks
Fig : Types of cracks (in welded joints) caused by thermal stresses that develop during
solidification and contraction of the weld bead and the surrounding structure. (a) Crater cracks
(b) Various types of cracks in butt and T joints.

89. 1.7. Lamellar tears
• Occurred due to the shrinkage of the restrained
components in the structure during cooling.
• Can be avoided by providing for shrinkage of the
members.
• Changing the joint design.
• Surface Damage : These discontinuities may
adversely affect the properties of welded structure,
particularly for notch sensitive metals.

90. 1.8. Residual Stresses
• Caused because of localized heating and cooling
during welding, expansion and contraction of the
weld area causes residual stresses in the work
piece.
• Distortion, Warping and buckling of welded parts
• Stress corrosion cracking
• Further distortion if a portion of the welded
structure is subsequently removed
• Reduced fatigue life

91. 1.9. Distortion of Parts After
Welding
Fig. Distortion of parts after welding. (a) Butt joints and (b) fillet welds. Distortion is
caused by differential thermal expansion and contraction of different regions of the welded
assembly.

92. 2. Weld Testing
2.1. Destructive Techniques
Fig. Destructive Techniques: (a) Specimen for longitudinal tension-shear testing; (b)
specimen for transfer tension-shear testing; (c) wraparound bend test method; (d) three-
point bending of welded specimens.

93. 2.2. Non-Destructive testing
• Often weld structures need to be tested Non-
Destructively
• Non-Destructive testing are :
 Visual
 Liquid-penetrant
 Radiographic
 Magnetic-particle
 Ultrasonic

95. Part 3: Turning operations

96. 1. Introduction
• Turning is a machining process to produce parts
round in shape by a single point tool on lathe
Machines.
• The cutting tool is fed either linearly in the
direction parallel or perpendicular to the axis of
rotation of the workpiece, or along a specified
path to produce complex rotational shapes.
• The primary motion of cutting in turning is the
rotation of the workpiece, and the secondary
motion of cutting is the feed motion of the
cutting tool (See figure on the next slide).

97. 2. Principal Surfaces and Motions

98. 3. Cutting conditions in turning
• Cutting speed in turning V in m/s is related to
the rotational speed of the workpiece by the
equation:
V = πDN (m/sec)
where D is the diameter of the workpiece, m;
N is the rotational speed of the workpiece,
rev/s (rpm).
• Feed in turning is generally expressed in mm
tr-1 (millimetres per revolution).

99. • The turning operation reduces the diameter of
the workpiece from the initial diameter Do to the
final diameter Df. The change in diameter is
actually two times depth of cut, d:
2d = Do - Df
• The volumetric rate of material removal (so-
called material removal rate, mrr) is defined by
mrr = Vfd
• When using this equation, care must be exercised
to assure that the units for V are consistent with
those for f and d.

100. 4. Operations in turning
• Turning of cylindrical surfaces
• Turning of flat surfaces
• Threading
• Form turning
• Knurling
• Drilling, Internal grooving and Boring

101. 4.1. Turning of cylindrical surfaces
The lathe can be used to reduce the diameter
of a part to a desired dimension. The resulting
machined surface is cylindrical.

102. 4.2. Turning of flat surfaces
A lathe can be used to create a smooth, flat
face very accurately perpendicular to the axis
of a cylindrical part.
Tool is fed radially or axially to create a flat
machined surface.

103. 4.3. Threading
 Threading is turning operation on lathe machine to
cut an helical groove on or in the workpiece, which is
actually a thread, by The single-point cutting tool at a
feed exactly equal to the thread pitch.
 The procedure calls for correct settings of the
machine, and also that the helix be restarted at the
same location each time if multiple passes are
required to cut the entire depth of thread.
 The tool point must be ground so that it has the
same profile as the thread to be cut.

104. Another possibility is to cut threads by means
of a thread die (external threads), or a tap
(internal threads). These operations are
generally performed manually for small
thread diameters.

105. 4.4. Form turning
Cutting tool has a shape that is imparted to
the workpiece by plunging the tool into the
workpiece.
In form turning, cutting tool is complex and
expensive but feed is linear and does not
require special machine tools or devices.

107. 4.5. Contour turning (profiling)
Cutting tool has a simple shape, but the feed
motion is complex; cutting tool is fed along a
contour thus creating a contoured shape on
the workpiece.
For profiling, special lathes* or devices are
required.
Producing tapers on a lathe is a specific task
and contour turning is just one of the possible
solutions**.

109. 4.6. Drilling, Internal grooving and
Boring

110. 4.7. Knurling
This is not a machining operation at all,
because it does not involve material removal.
Instead, it is a metal forming operation used
to produce a regular crosshatched pattern in
the work surface.

112. 5. Lathes
• A lathe is a machine tool that rotates the workpiece
against a tool whose position it controls.
• The spindle (see picture in the next page) is the part of the lathe
that rotates. Various work holding attachments such
as three jaw chucks, collets, and centers can be held
in the spindle. The spindle is driven by an electric
motor through a system of belt drives and gear
trains.
• Spindle rotational speed is controlled by varying the
geometry of the drive train.

113. 6. Principal components of a lathe

114. • The tailstock can be used to support the end of the
workpiece with a center, or to hold tools for drilling,
reaming, threading, or cutting tapers.
• The carriage controls and supports the cutting tool.
It consists of:
a saddle that slides along the ways;
an apron that controls the feed mechanisms;
a cross slide that controls transverse motion of the
tool;
a tool post that holds the cutting tools.

115. 7. Work holding methods in lathes

116. 8. Turning tapers on lathes
• A taper is a conical shape.
• The tailstock offset h is defined by
h = Lsinα
where L is the length of workpiece, and α is the half of the taper angle.

117. 9. Cutting tools

118. Left and Right-hand turning tool
bit

119. Shapes of Tool Bits

120. END OF PART 3
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