LATHE_OPERATIONS_1.ppt basics in manufacturing processes

Copyright © The McGraw-Hill Companies, Inc.
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PowerPoint to accompany
Krar • Gill • Smid
Technology of Machine Tools
6th
Edition
The Lathe
Section 11

History
• Lathe forerunner of all machine tools
• First application was potter's wheel
– Rotated clay and enabled it to be formed into
cylindrical shape
• Very versatile (many attachments)
– Used for turning, tapering, form turning, screw
cutting, facing, drilling, boring, spinning,
grinding and polishing operations
• Cutting tool fed either parallel or right angles

Special Types of Lathes
• Engine lathe
– Not production lathe, found in school shops,
toolrooms, and jobbing shops
– Basic to all lathes
• Turret lathe
– Used when many duplicate parts required
– Equipped with multisided toolpost (turret) to
which several different cutting tools mounted
• Employed in given sequence

6th
Edition
Engine Lathe Parts
Unit 45

Engine Lathe
• Accurate and versatile machine
• Operations
– Turning, tapering, form turning, threading,
facing, drilling, boring, grinding, and polishing
• Three common
– Toolroom
– Heavy-duty
– Gap-bed

Lathe Size and Capacity
• Designated by largest work diameter that
can be swung over lathe ways and generally
the maximum distance between centers
• Manufactured in wide range of sizes
– Most common: 9- to 30- in. swing with
capacity of 16 in. to 12 feet between centers
– Typical lathe: 13 in. swing, 6 ft long bed, 36 in.
– Average metric lathe: 230-330 mm swing and
bed length of 500 – 3000 mm

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Indicated by the swing
and the length of the bed
Lathe Size

Parts of the Lathe
Bed
Headstock
Quick
Change
Gearbox
Tailstock
Carriage

Setting Speeds on a Lathe
• Speeds measured in revolutions per minute
– Changed by stepped pulleys or gear levers
• Belt-driven lathe
– Various speeds obtained by changing flat belt
and back gear drive
• Geared-head lathe
– Speeds changed by moving speed levers into
proper positions according to r/min chart
fastened to headstock
Safety Note!! NEVER change speeds
when lathe is running.

Shear Pins and Slip Clutches
• Prevents damage to feed mechanism from
overload or sudden torque
• Shear pins
– Made of brass
– Found on feed rod, lead screw, and end gear train
• Spring-loaded slip clutches
– Found only on feed rods
– When feed mechanism overloaded, shear pin will
break or slip clutch will slip causing feed to stop

Shear pin in end gear
train prevents damage
to the gears in case
of an overload
Spring-ball clutch
will slip when too
much strain is
applied to feed rod

6th
Edition
Lathe Accessories
Unit 46

46-15
Lathe Accessories
• Divided into two categories
– Work-holding, -supporting, and –driving devices
• Lathe centers, chucks, faceplates
• Mandrels, steady and follower rests
• Lathe dogs, drive plates
– Cutting-tool-holding devices
• Straight and offset toolholders
• Threading toolholders, boring bars
• Turret-type toolposts

46-16
Lathe Centers
• Work to be turned between centers must
have center hole drilled in each end
– Provides bearing surface
• Support during cutting
• Most common have
solid Morse taper shank
60º centers, steel with carbide tips
• Care to adjust and lubricate occasionally

46-17
Chucks
• Used extensively for holding work for
machining operations
– Work large or unusual shape
• Most commonly used lathe chucks
– Three-jaw universal
– Four-jaw independent
– Collet chuck

46-18
Three-jaw Universal Chuck
• Holds round and hexagonal work
• Grasps work quickly and accurate within
few thousandths/inch
• Three jaws move
simultaneously when
adjusted by chuck wrench
– Caused by scroll plate into
which all three jaws fit
• Two sets of jaw: outside chucking and
inside chucking

46-19
Four-Jaw Independent Chuck
• Used to hold round, square, hexagonal, and
irregularly shaped workpieces
• Has four jaws
– Each can be adjusted independently by chuck
wrench
• Jaws can be reversed to hold work by inside
diameter

46-20
Headstock Spindles
Universal and independent chuck fitted to
three types of headstock spindles
1. Threaded spindle nose
– Screws on in a
clockwise direction
2. Tapered spindle nose
– Held by lock nut
that tightens on chuck

46-21
Headstock Spindles
3. Cam-lock spindle nose
• Held by tightening cam-locks using T-wrench
• Chuck aligned by taper
on spindle nose
Registration lines on spindle nose
Registration lines on cam-lock
Cam-locks
Cam-lock mating stud on
chuck or faceplate

46-22
Collet Chuck
• Most accurate chuck
• Used for high-precision work
• Spring collets available to hold round,
square, or hexagon-shaped workpieces
• Each collet has range of only few
thousandths of an inch over or under size
stamped on collet

46-23
|
Collet Chuck
Special adapter fitted into taper of headstock spindle,
and hollow draw bar having internal thread inserted
in opposite end of headstock spindle. It draws collet
into tapered adapter causing collet to tighten on workpiece.

46-24
Types of Lathe Dogs
• Standard bent-tail lathe dog
– Most commonly used for round
workpieces
– Available with square-head
setscrews of headless setscrews
• Straight-tail lathe dog
– Driven by stud in driveplate
– Used in precision turning

46-25
Types of Lathe Dogs
• Safety clamp lathe dog
– Used to hold variety of work
– Wide range of adjustment
• Clamp lathe dog
– Wider range
than others
– Used on all shapes

46-26
Left-Hand Offset Toolholder
• Offset to the right
• Designed for machining work close to
chuck or faceplate and cutting right to left
• Designated by letter L

46-27
Right-Hand Offset Toolholder
• Offset to the left
• Designed for machining work close to the
tailstock and cutting left to right
– Also for facing operations
• Designated by letter R

46-28
Straight Toolholder
• General-purpose type
• Used for taking cuts in either direction and
for general machining operations
• Designated by letter S

46-29
Toolholders for Indexable
Carbide Inserts
• Held in holder by cam action or clamps
• Types available
– Conventional
– Turret-type
– Heavy-duty toolposts

46-30
Cutting-Off (Parting) Tools
• Used when work must be grooved or
parted off
• Long, thin cutting-off blade locked
securely in toolholder by either cam lock or
locking nut
• Three types of parting toolholders
– Left-hand
– Right-hand
– Straight

46-31
Threading Toolholder
• Designed to hold special form-relieved
thread-cutting tool
• Has accurately ground 60º angle
– Maintained throughout life of tool
• Only top of cutting surface sharpened when
becomes dull

46-32
Super Quick-Change Toolpost

6th
Edition
Cutting Speed, Feed,
and Depth of Cut
Unit 47

47-34
Cutting Speed
• Rate at which point on work circumference
travels past cutting tool
• Always expressed in feet per minute (ft/min)
or meters per minute (m/min)
• Important to use correct speed for material
– Too high: cutting-tool breaks down rapidly
– Too low: time lost, low production rates

47-35
Lathe Cutting Speeds in Feet and Meters per
Minute Using High-Speed Steel Toolbit
Turning and Boring
Rough Cut Finish Cut Threading
l ft/min m/min ft/min m/min ft/min
steel 90 27 100 30 35 11
el 70 21 90 27 30 9
n 60 18 80 24 25 8
90 27 100 30 25 8
m 200 61 300 93 60 18

47-36
Calculating Lathe Spindle Speed
• Given in revolutions per minute
• Cutting speed of metal and diameter of
work must be known
• Proper spindle speed set by dividing
CS (in/min) by circumference of work (in)
D
4
x
CS
D
12
x
CS
r/min 



47-37
Example:
D
4
x
CS
r/min 
Calculate r/min required to rough-turn 2 in. diameter
piece of machine steel (CS 90):
180
2
4
x
90
r/min 

D
320
x
CS
r/min 
Metric Formula

47-38
Lathe Feed
• Distance cutting tool advances along length
of work for every revolution of the spindle
• Feed of engine lathe dependent on speed of
lead screw for feed rod
– Speed controlled by change gears in
quick-change gearbox

47-39
Two Cuts Used to Bring
Diameter to Size
• Roughing cut
– Purpose to remove excess material quickly
– Coarse feed: surface finish not too important
• .010- to .015-in. (0.25- to 0.4-mm)
• Finishing cut
– Used to bring diameter to size
– Fine feed: Produce good finish
• .003- to .005-in (0.07- to 0.012-mm)

47-40
Feeds for Various Materials
(using high-speed steel cutting tool)
Rough Cuts Finish Cuts
Material in. mm in. mm
Machine steel .010–.020 0.25–0.5 .003–.010 0.07–0.25
Tool steel .010–.020 0.25–0.5 .003–.010 0.07–0.25
Cast iron .015–.025 0.4–0.65 .005–.012 0.13–0.3
Bronze .015–.025 0.4–0.65 .003–.010 0.07–0.25
Aluminum .015–.030 0.4–0.75 .005–.010 0.13–0.25

47-41
Depth of Cut
• Depth of chip taken by cutting tool and one-
half total amount removed from workpiece
in one cut
• Only one roughing and one finishing cut
– Roughing cut should be deep as possible to
reduce diameter to within .030 to .040 in. (0.76
to 1 mm) of size required
– Finishing cut should not be less than .005 in.

47-42
Example: Depth of cut on a lathe

47-43
Factors Determining Depth of
Rough-Turning Cut
• Condition of machine
• Type and shape of cutting tool used
• Rigidity of workpiece, machine, and cutting
tool
• Rate of feed

47-44
Inch System
• Circumference of crossfeed and compound
rest screw collars divided into 100-125
equal divisions
– Each has value of .001 in.
• Turn crossfeed screw clockwise 10 graduations,
cutting tool moved .010 in. toward work
• Lathe revolves, so .010 depth of cut taken from
entire work circumference reducing diameter .020 in.
• Check machine for its' graduations

47-45
On machines where the workpiece revolves,
the cutting tool should be set in for only half
the amount to be removed from the diameter.

47-46
On machines where the workpiece does not
revolve, the cutting tool should be set in for
the amount of material to be removed.

47-47
Hints on Graduated Collar Use
1. Make sure collar is secure before setting a
depth of cut
2. All depths of cut must be made by feeding
cutting tool toward workpiece
3. If graduated collar turned past desired
setting, must be turned backward half-turn
and fed into proper setting to remove
backlash
4. Never hold graduated collar when setting
depth of cut

47-48
5. Graduated collar on compound rest can be
used for accurately setting depth of cut
• Shoulder turning
• Compound rest set at 90º to cross-slide
• Lock carriage in place
• Spacing of shoulders to within .001 in. accuracy
• Facing
• Compound rest swung to 30º, amount removed from
length of work = ½ amount of feed on collar
• Machining accurate diameters
• Set compound rest to 84º16' to the cross-slide
• .001 in movement = .0001-in. infeed movement

47-49
The compound rest is set at 84º16' for
making fine settings.

6th
Edition
Lathe Safety
Unit 48

48-51
Safety
• Be aware of safety requirements in any area
of shop
• Always attempt to observe safety rules
• Failure results in:
– Serious injury
– Resultant loss of time and pay
– Loss of production to company

48-52
Safety Precautions
• Lathe hazardous if not operated properly
• Important to keep machine and surrounding
area clean and tidy
• Accidents usually caused by carelessness

48-53
Safety Precautions
• Always wear approved safety glasses
• Rollup sleeves, remove tie and tuck in loose
clothing
• Never wear ring or watch

48-54
Safety Precautions
• Do not operate lathe until understand controls
• Never operate machine if safety guards
removed
• Stop lathe before measure work or clean, oil
or adjust machine
• Do not use rag to clean work or machine
when in operation
– Rag can get caught and drag in hand

48-55
Safety Precautions
• Never attempt to stop a lathe chuck or
driveplate by hand
• Be sure chuck or faceplate mounted securely
before starting
– If loose, becomes dangerous missile
• Always remove chuck wrench after use
– Fly out and injure someone
– Become jammed, damaging wrench or lathe

48-56
Safety Precautions
• Move carriage to farthest position of cut and
revolve lathe spindle one turn by hand
– Ensure all parts clear without jamming
– Prevent accident and damage to lathe
• Keep floor around machine free from grease,
oil, metal cuttings, tools and workpieces
– Oil and grease can cause falls
– Objects on floor become tripping hazards

48-57
Safety Precautions
• Avoid horseplay at all times
• Always remove chips with brush
– Chips can cause cuts if use hands
– Chips become embedded if use cloths
• Always remove sharp toolbit from
toolholder when polishing, filing, cleaning,
or making adjustments

6th
Edition
Mounting, Removing,
and Aligning Lathe
Centers
Unit 49

49-59
Objectives
• Mount and/or remove lathe centers
properly
• Align lathe centers by visual, trial-cut,
and dial-indicator methods

49-60
Lathe Centers
• Work machined between centers turned for
some portion of length, then reversed, and
other end finished
• Critical when machining work between
centers that live center be absolutely true
– Concentric work

49-61
To Mount Lathe Centers
• Remove any burrs from lathe spindle,
centers, or spindle sleeves
• Clean tapers on lathe centers and in
headstock and tailstock spindles
• Partially insert cleaned center in lathe spindle
• Force center into spindle
• Follow same procedure when mounting
tailstock center
• Check trueness of center

49-62
To Remove Lathe Centers
• Live center
– Use knockout bar pushed through headstock
spindle (slight tap)
– Use cloth over center and hold to prevent damage
• Dead center
– Turn tailstock handwheel to draw spindle back
into tailstock
• End of screw contacts end of dead center, forcing it
out of spindle

49-63
Alignment of Lathe Centers
• Parallel diameter produced when lathe
center aligned
• Three common methods
used to align
1. Aligning centerlines
on back of tailstock
with each other
– Only a visual check
and not too accurate

49-64
Alignment of Lathe Centers
2. Using the trial-cut
method where small
cut taken from each
end of work and
diameters measured with a micrometer
3. Using parallel test bar and dial indicator
• Fastest and most accurate method

49-65
To Align Centers by Adjusting
the Tailstock
1. Loosen tailstock clamp nut or level
2. Loosen on of the adjusting screws,
depending on direction tailstock must be
moved and tighten other until line on top
aligns with line on bottom half
3. Tighten screw to lock both halves in place
4. Make sure tailstock lines still aligned
5. Lock tailstock clamp nut or lever

49-66
To Align Centers by
Trial-Cut Method
1. Take a light cut (~.005 in.) to true
diameter from section A at tailstock end
for .250 in. long
2. Stop feed and note reading on graduated
collar of crossfeed handle
3. Move cutting tool away from work with
crossfeed handle
4. Bring cutting tool close to headstock end

49-67
To Align Centers by
Trial-Cut Method
5. Return cutting tool to same graduated
collar setting as at section A
6. Cut a .500-in (13 mm) length at section B
and stop lathe
7. Measure both diameters with micrometer

49-68
To Align Centers by
Trial-Cut Method
8. If both diameters not same size, adjust
tailstock either toward or away from
cutting tool ½ difference of two readings
9. Take another light cut at A and B at same
crossfeed graduated collar setting.
Measure diameters and adjust tailstock.

49-69
To Align Centers Using Dial
Indicator and Test Bar
1. Clean lathe and work center, mount test
bar
2. Adjust test bar snugly between centers and
tighten tailstock spindle clamp
3. Mount dial indicator on toolpost or lathe
carriage
– Indicator plunger should be parallel to lathe
bed and contact point set on center

49-70
4. Adjust cross-slide
– Indicator registers approximately .025 in at
tailstock, indicator bezel to 0
5. Move carriage by hand so indicator
registers on diameter at headstock end and
not indicator reading
6. If both indicator readings not same, adjust
tailstock with adjusting screws until
indicator registers same at both ends

49-71
7. Tighten adjusting screw that was loosened
8. Tighten tailstock clamp nut
9. Adjust tailstock spindle until test bar snug
between lathe centers
10. Recheck indicator readings at both ends
and adjust tailstock, if necessary

6th
Edition
Grinding Lathe
Cutting Tools
Unit 50

50-73
Grinding Lathe Cutting Tool
• Wide variety of cutting tools for lathe
– All have certain angles and clearances regardless
of shape
Shape and Dimensions of General-purpose Lathe Toolbit

50-74
To Grind a
General-Purpose Toolbit
1. Dress face of grinding wheel
2. Grip toolbit firmly, supporting hands on grinder
toolrest
3. Hold toolbit at proper
angel to grind cutting
edge angle
• Tilt bottom of toolbit
toward wheel and
grind 10º side relief
or clearance angle

50-75
Cutting edge ~ ½ In long and extend
over ¼ width of toolbit
10º side relief or
clearance angle

50-76
4. While grinding, move toolbit back and
forth across face of wheel
• Prevents grooving wheel
5. Toolbit must be cooled frequently during
grinding
• Never overheat toolbit!
• Never quench stellite or cemented-carbide
tools
• Never grind carbides with aluminum oxide
wheel

50-77
6. Grind end cutting edge so it forms angle of
a little less than 90º with side cutting edge
– Hold tool so that end cutting edge angle and
end relief angle of 15º ground at same time
70º to 80º Point Angle

50-78
7. Using toolbit grinding gage, check amount
of end relief when toolbit is in toolholder

50-79
8. Hold top of toolbit approximately 45º to
axis of wheel and grind side rake to
approximately 14º
– Do not grind below top of toolbit
• Creates a chip trap
Side rake ground the length
of the cutting edge

50-80
9. Grind slight radius on point of cutting
tool, being sure to maintain same front
and side clearance angle
10. With oilstone, hone cutting edge of toolbit
slightly
• Lengthen life of toolbit
• Enable it to produce better surface finish on
workpiece

6th
Edition
Machining
Between Centers
Unit 52

52-82
Machining Between Centers
• Training programs (schools)
– Remove and replace work in lathe many times
before completed
– Need assurance that machined diameter will run
true with other diameters
• Machining between centers saves time in setting up
• Common operations
– Facing, rough and finish-turning, shoulder
turning, filing and polishing

52-83
Setting Up a Cutting Tool
1. Move toolpost to the left-hand side of the T-slot
in the
compound
rest
2. Mount tool-
holder in
toolpost so
setscrew in
toolholder 1 in.
beyond toolpost

52-84
Heavy Cuts: Set toolholder at right
angles to work

52-85
Setting Up a Cutting Tool: cont.
3. Insert proper cutting tool into toolholder,
having tool extend .500 in. beyond
toolholder and never more than twice its
thickness
4. Set cutting-tool point to center height
• Check it against lathe center point
5. Tighten toolpost securely to prevent it
from moving during a cut

52-86
Purposes of a Trial Cut
• Produce accurate turned diameter
– Measured with micrometer
• Set cutting-tool point to the diameter
• Set crossfeed micrometer collar to the
diameter

52-87
Procedure to Take a Trial Cut
1. Set up workpiece and cutting tool as for
turning
2. Set proper speeds and feed to suit material
3. Start lathe and position toolbit over work
approximately .125 in. from end
4. Turn compound rest handle clockwise ¼
of a turn to remove any backlash

52-88
5. feed toolbit into work by turning crossfeed
handle clockwise until light ring appears
around entire circumference of work
6. Do NOT move crossfeed handle setting
7. Turn carriage handwheel until toolbit clears
end of workpiece by about .060 in.
8. Turn crossfeed handle clockwise
about .010 in. and take trial cut .250 in.
along length of work
9. Disengage automatic feed and clear toolbit
past end of work with carriage handwheel

52-89
10. Stop the lathe
11. Test accuracy of micrometer by cleaning
and closing measuring faces and then
measure trial-cut diameter
12. Calculate how much material must still be
removed from diameter of work
13. Turn crossfeed handle clockwise ½
amount of material to be removed

52-90
14. Take another trial cut .250 in. long and
stop the lathe
15. Clear toolbit over end of work with
carriage handwheel
16. Measure diameter and readjust crossfeed
handle until diameter is correct
17. Machine diameter to length

52-91
Rough Turning
• Removes as much metal as possible in
shortest length of time
• Accuracy and surface finish are not
important in this operation
– .020- to .030-in. feed recommended
• Work rough-turned to
– Within .030 in. of finished size when
removing up to .500 in. diameter
– Within .060 in. when removing > .500 in.

52-92
Procedure for Rough Turning
1. Set lathe to correct speed for type and size
of material being cut
2. Adjust quick-change gearbox for a .010-
to .030-in. feed
• Depends on depth of cut and condition of
machine
3. Move toolholder to left-hand side of
compound rest and set toolbit height to
center

52-93
4. Tighten toolpost securely to prevent
toolholder from moving during machining
5. Take light trial cut at right-hand end of
work for a .250 in. length
6. Measure work and adjust toolbit for
proper depth of cut
7. Cut along for .250 in., stop lathe, and
check diameter for size
1. Diameter .030 in. over finish size
8. Readjust depth of cut, if necessary

52-94
Finish Turning
• Follows rough turning
• Produces smooth surface finish and cuts
work to an accurate size
• Factors affecting type of surface finish
– Condition of cutting tool
– Rigidity of machine and work
– Lathe speeds and feeds

52-95
Procedure For Finish Turning
1. Make sure cutting edge of toolbit free
from nicks, burrs, etc.
2. Set toolbit on center; check it against lathe
center point
3. Set lathe to recommended speed and feed

52-96
4. Take light trial cut .250 in. long at right-
hand end of work
• Produce true diameter
• Set cutting tool to diameter
• Set graduated collar to diameter
5. Stop lathe and measure diameter
6. Set depth of cut for half amount of
material to be removed
7. Cut along for .250 in., stop lathe, check
8. Readjust depth of cut and finish-turn

52-97
Filing in a Lathe
• Only to remove small amount of stock,
remove burrs, or round off sharp corners
• Work should be turned to within .002 to .003
in. of size
• For safety, file with left hand so arms and
hands kept clear of revolving chuck
• Remove toolbit from toolholder before filing
• Cover lathe bed with paper before filing

52-98
Procedure to File in a Lathe
1. Set spindle speed to twice that for turning
2. Mount work between centers, lubricate,
and carefully adjust dead center in work
3. Move carriage as far to right as possible
and remove toolpost
4. Disengage lead screw and feed rod
5. Select 10- or 12-in. mill file or long-angle
lathe file

52-99
6. Start lathe
7. Grasp file handle in left hand and support
file point with fingers of right hand

52-100
8. Apply light pressure and push file forward
to its full length; release pressure on
return stroke
9. Move file about half width of file for each
stroke and continue filing until finished
• Use 30-40 strokes per minute
10. Safety precautions
• Roll sleeves above elbow
• Remove watches and rings
• Never use file without properly fitted handle
• Never apply too much pressure
• Clean file frequently with file brush

52-101
Procedure for
Polishing in a Lathe
1. Select correct type and grade of abrasive
cloth for finish desired
• Piece about 6 – 8 in. long and 1 in. wide
• Use aluminum oxide abrasive cloth for
ferrous metals
• Use silicon carbide abrasive cloth should be
used for nonferrous metals
2. Set lathe to run at high speed
3. Disengage feed rod and lead screw

52-102
4. Remove toolpost and toolholder
5. Lubricate and adjust dead center
6. Roll sleeves up above elbows and tuck in
any loose clothing
7. Start lathe
8. Hold abrasive cloth on work
9. With right hand, press cloth firmly on
work while tightly holding other end of
abrasive cloth with left hand
10. Move cloth slowly back and forth

52-103
Shoulder
• Shoulder: the change in diameters, or step,
when turning more than one diameter on a
piece of work
• Three common types of shoulders
– Square
– Filleted
– Angular or Tapered

52-104
Three Types of Shoulders

6th
Edition
Knurling, Grooving,
and Form Turning
Unit 53

53-106
Knurling
• Process if impressing a diamond-shaped or
straight-line patter into the surface of the
workpiece
– Improve its appearance
– Provide better gripping surface
– Increase workpiece diameter when press fit
required

53-107
Knurling
• Diamond- and
straight-pattern
rolls available in
three styles
– Fine
– Medium
– Course

53-108
Knurling Tool
• Toolpost-type toolholder on which pair of
hardened-steel rolls mounted
Knurling tool with
one set of rolls in
self-centering head
Knurling tool with
three sets of rolls
in revolving head

53-109
Universal Knurling Tool System
• Dovetailed shank and as many as seven
interchangeable knurling heads that can
produce wide range of knurling patterns
• Combines in one tool
– Versatility
– Rigidity
– Ease of handling
– Simplicity

53-110
Procedure to Knurl in a Lathe
1. Mount work between centers and mark
required length to be knurled
• If work held in chuck for knurling, right end
of work should be supported with revolving
tailstock center
2. Set lathe to run at one-quarter speed
required for turning
3. Set carriage feed to .015 to .030 in.

53-111
4. Set center of floating head of knurling tool
even with dead-center point
5. Set knurling tool at right angles to
workpiece and tighten it securely

53-112
6. Start machine and lightly touch rolls
against work to check tracking
7. Move knurling tool to end of work so
only half the roll face bears against work
8. Force knurling tool into work
approximately .025 in. and start lathe
OR
Start lathe and then force knurling tool into
work until diamond pattern come to point

53-113
9. Stop lathe and examine pattern
10. Once pattern correct, engage automatic
carriage feed and apply cutting fluid to
knurling rolls
11. Knurl to proper length and depth
• Do not disengage feed until full length has
been knurled; otherwise, rings will be formed
on knurled pattern
12. If knurling pattern not to point after length
has been knurled, reverse lathe feed and
take another pass across work

53-114
Grooving
Square
Round
V-shaped
• Done at end of thread to
permit full travel of nut up
to a shoulder or at edge of
shoulder for proper fit
• Also called recessing,
undercutting, or necking
• Rounded grooves used
where there is strain on
part

53-115
Procedure to Cut a Groove
1. Grind toolbit to desired size and shape of
groove required
2. Lay out location of groove
3. Set lathe to half the speed for turning
4. Mount workpiece in lathe
5. Set toolbit to center height

53-116
6. Locate toolbit on work at position where
groove is to be cut
7. Start lathe and feed cutting tool toward
work using crossfeed handle until toolbit
marks work lightly
8. Hold crossfeed handle in position and set
graduated collar to zero
9. Calculate how far crossfeed screw must be
turned to cut groove to proper depth
10. Feed toolbit into work slowly using
crossfeed handle

53-117
11. Apply cutting fluid to point of cutting tool
• To ensure cutting tool will not bind in
groove, move carriage slightly to left and to
right while grooving
• Should chatter develop, reduce spindle speed
12. Stop lathe and check depth of groove with
outside calipers or knife-edge verniers
Safety note: Always wear safety goggles when
grooving on a lathe

6th
Edition
Threads and Thread
Cutting
Unit 55

55-119
Threads
• Used for hundreds of years for holding parts
together, making adjustments, and
transmitting power and motion
• Art of producing threads continually
improved
• Massed-produced by taps, dies, thread
rolling, thread milling, and grinding

55-120
Threads
• Thread
– Helical ridge of uniform section formed on
inside or outside of cylinder or cone
• Used for several purposes:
– Fasten devices such as screws, bolts, studs, and
nuts
– Provide accurate measurement, as in micrometer
– Transmit motion
– Increase force

55-121
Thread
Terminology

55-122
Thread Terminology
• Screw thread
– Helical ridge of uniform section formed on
inside or outside of cylinder or cone
• External thread
– Cut on external surface or cone
• Internal thread
– Produced on inside of cylinder or cone

55-123
• Major diameter
– Largest diameter of external or internal thread
• Minor diameter
– Smallest diameter of external or internal thread
• Pitch diameter
– Diameter of imaginary cylinder that passes
through thread at point where groove and thread
widths are equal
– Equal to major diameter minus single depth of
thread
– Tolerance and allowances given at pitch
diameter line

55-124
• Number of threads per inch
– Number of crests or roots per inch of threaded
section (Does not apply to metric threads)
• Pitch
– Distance from point on one thread to
corresponding point on next thread, measured
parallel to axis
– Expressed in millimeters for metric threads
• Lead
– Distance screw thread advances axially in one
revolution (single-start thread, lead = pitch)

55-125
• Root
– Bottom surface joining sides of two adjacent
threads
– External thread on minor diameter
– Internal thread on major diameter
• Crest
– Top surface joining two sides of thread
– External thread on major diameter
– Internal thread on minor diameter
• Flank
– Thread surface that connects crest with root

55-126
• Depth of thread
– Distance between crest and root measured
perpendicular to axis
• Angle of thread
– Included angle between sides of thread
measured in axial plane
• Helix angle
– Angle that thread makes with plane
perpendicular to thread axis

55-127
• Right-hand thread
– Helical ridge of uniform cross section onto
which nut is threaded in clockwise direction
– When cut on lathe, toolbit
advanced from right to left
• Left-hand thread
– Helical ridge of uniform cross section onto
which nut is threaded in counterclockwise
direction
– When cut on lathe, toolbit
advanced from left to right

55-128
Thread Forms
• April, 1975 ISO came to an agreement
covering standard metric thread profile
– Specifies sizes and pitches for various threads
in new ISO Metric Thread Standard
– Has 25 thread sizes, range in diameter from 1.6
to 100 mm
– Identified by letter M, nominal diameter, and
pitch M 5 X 0.8

55-129
American National Standard Thread
• Divided into four main series, all having
same shape and proportions
– National Coarse (NC)
– National Fine (NF)
– National Special (NS)
– National Pipe (NPT)
• Has 60º angle with root and crest truncated
to 1/8th
the pitch
• Used in fabrication, machine construction

55-130
N
P
F
N
P
D
.125
or
x
.125
.6134
or
x
6134
.



55-131
Unified Thread
• Developed by U.S., Britain, and Canada for
standardized thread system
• Combination of British Standard Whitworth and

55-132
N
P
F
N
P
F
N
P
D
N
P
D
.250
or
x
.250
thread)
(internal
.125
or
x
.125
thread)
(external
.5413
or
x
5413
.
thread)
(internal
.6134
or
x
6134
.
thread)
(external





55-133
American National Acme Thread
• Replacing square thread in many cases
• Used for feed screws, jacks, and vises
D = minimum .500P
= maximum .500P + 0.010
F = .3707P
C = .3707P - .0052
(for maximum depth)

55-134
Brown & Sharpe Worm Thread
• Used to mesh worm gears and transmit
motion between two shafts at right angles to
each other but not in same plane
D = .6866P
F = .335P
C = .310P

55-135
Square Thread
• Being replaced by Acme thread because of
difficulty in cutting it
• Often found on vises
and jack screws
D = .500P
F = .500P
C = .500P + .002

55-136
International Metric thread
• Standardized thread used in Europe
F = 0.125P
R = 0.0633P (maximum)
= 0.054P (minimum)
D = 0.7035P (maximum)
= 0.6855P (minimum)

55-137
Thread Fits and Classifications
• Fit
– Relationship between two mating parts
– Determined by amount of clearance or
interference when they are assembled
• Nominal size
– Designation used to identify size of part
• Actual size
– Measured size of thread or part
– Basic size: size from which tolerances are set

55-138
Allowance
• Permissible difference between largest
external thread and smallest internal thread
• Difference produces tightest fit acceptable
for any given classification
The allowance for a 1 in.—8 UNC Class 2A and 2B fit is:
Minimum pitch diameter of the
internal thread (2B) = .9188 in.
Maximum pitch diameter of the
external thread (2A) = .9168 in.
Allowance = .002 in.

55-139
Tolerance
• Variation permitted in part size
• May be expressed as plus, minus, or both
• Total tolerance is sum of plus and minus tolerances
• In Unified and National systems, tolerance is plus
on external threads and minus on internal threads
Tolerance = .0068 in.
The tolerance for a 1 in.—8 UNC Class 2A thread is:

55-140
Limits
• Maximum and minimum dimensions of part
external thread (2A) = .9168 in..
The limits for a 1 in.—8 UNC Class 2A thread are:

55-141
Three Categories of Unified
Thread Fits
• External threads classified as 1A, 2A, and 3A and
internal threads as 1B, 2B, 3B
• Classes 1A and 1B
– Threads for work that must be assembled
– Loosest fit
– Used for most commercial fasteners
– Medium or free fit
– Used where more accurate fit and lead required
– No allowance provided

55-142
Thread Calculations: Example 1
To cut a correct thread on a lathe, it is necessary first to
make calculations so thread will have the proper dimensions.
D = single depth of thread
P = pitch
in.
.061
.100
x
.61343
x
61343
.
in.
100
.
10
1
1






P
D
tpi
P
Calculate pitch, depth, minor diameter, and width of flat
for a ¾—10 UNC thread.
in.
0125
.
10
1
x
8
1
8
flat
of
Width
in.
628
.
.061)
(.061
-
.75
)
(
-
dia
Major
dia
Minor








P
D
D

55-143
Thread Calculations: Example 2
P = pitch = 1 mm
D = 0.54127 x 1
= 0.54 mm
What are the pitch, depth, minor diameter, width of crest
and width of root for an M 6.3 X 1 thread?
mm
125
.
0
1
x
125
.
0
x
.125
0
crest
of
Width
mm
22
.
5
.54)
(.54
-
6.3
)
(
-
dia
Major
dia
Minor








P
D
D
mm
25
.
0
1
x
0.25
x
25
.
0
root
of
Width


 P

55-144
Procedure to Set the Quick-
Change Gearbox for Threading
1. Check drawing for thread pitch required
2. From chart on quick-change gearbox, find
whole number that represents pitch in
threads per inch or in millimeters
3. With lathe stopped, engage tumbler lever
in hole, which is in line with the pitch
4. Set top lever in proper position as
indicated on chart

55-145
5. Engage sliding gear in or out as required
6. Turn lathe spindle by hand to ensure that
lead screw revolves
7. Recheck lever settings to avoid errors

55-146
Thread-Chasing dial
• Lathe spindle and
lead screw must be
in same relative
position for each cut
– Thread-chasing dial
attached to carriage for
this purpose
• Dial has eight divisions
– Even threads use any division
– Odd threads either numbered
or unnumbered: not both

55-147
Thread Cutting
• Produces a helical ridge of uniform section
on workpiece
• Performed by taking successive cuts with
threading toolbit of same shape as thread
form required
• Work may be held between centers or in
chuck

55-148
Procedure to Set Up a Lathe for
Threading (60º Thread)
1. Set lathe speed to ¼ speed used for turning
2. Set quick-change gearbox for required pitch
in threads per inch or in millimeters
3. Engage lead screw
4. Secure 60º threading toolbit and check
angle using thread center gage
5. Set compound rest at 29º to right; set to left
for left-hand thread

55-149
6. Set cutting tool to height of lathe center
point
7. Mount work between centers
• Make sure lathe dog is tight on work
• If work mounted in chuck, it must be held
tightly
8. Set toolbit at right angles to work, using
thread center gage
9. Arrange apron controls to allow split-nut
lever to be engaged

55-150
Thread-Cutting Operation
Procedure to cut a 60º thread
1. Check major diameter of work for size
2. Start lathe and chamfer end of workpiece
with side of threading tool to just below
minor diameter of thread
3. Mark length to be threaded by cutting
light groove at this point with threading
tool while lathe revolving

55-151
4. Move carriage until point of threading tool
near right-hand end of work
5. Turn crossfeed handle until threading tool
close to diameter, but stop when handle is at
3 o'clock position
6. Hold crossfeed handle in this position and
set graduated collar to zero
7. Turn compound rest handle until threading
tool lightly marks work

55-152
8. Move carriage to right until toolbit clears
end of work
9. Feed compound rest clockwise about .003 in.
10. Engage split-nut lever on correct line of
thread-chasing dial and take trial cut along
length to be threaded
11. At end of cut, turn crossfeed handle
counterclockwise to move toolbit away from
work and disengage split-nut lever

55-153
12. Stop lathe and check number of tpi with
thread pitch gage, rule, or center gage
13. After each cut, turn carriage handwheel to
bring toolbit to start of thread and return
crossfeed handle to zero
14. Set depth of all threading cuts with
compound rest handle
• See Table 55.2 and Table 55.3

55-154
When tool is fed in at 29º, most of the cutting
is done by the leading edge of toolbit.

55-155
Table 55.2 Depth settings for cutting
60° national form threads*
Compound Rest Setting
tpi 0° 30° 29°
24 .027 .031 .0308
20 .0325 .0375 .037
18 .036 .0417 .041
16 .0405 .0468 .046
14 .0465 .0537 .0525
13 .050 .0577 .057
11 .059 .068 .0674
Portion of table taken
from textbook

55-156
15. Apply cutting fluid and take successive
cuts until top (crest) and bottom (root) of
thread are same width
16. Remove burrs from top of thread with file
17. Check thread with master nut and take
further cuts

55-157
Six Ways to Check Threads
• Depends on accuracy required:
1. Master nut or screw
2. Thread micrometer
3. Three wires
4. Thread roll or snap gage
5. Thread ring or plug gage
6. Optical comparator

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