The document outlines the technologies and procedures involved in thread cutting on lathes, covering various types of threads such as external, internal, and acme threads. It details thread terminology, measurements, and the setup required for cutting both metric and unified threads, including tolerances and allowances for different thread fits. Additionally, it provides step-by-step procedures for setting up a lathe for threading operations and verifying thread accuracy.

1. Copyright © The McGraw-Hill Companies, Inc.
Permission required for reproduction or display.
PowerPoint to accompany
Krar • Gill • Smid
Technology of Machine Tools
6th
Edition
Threads and Thread
Cutting
Unit 55

2. 55-2
Objectives
• Recognize and state the purposes of six
common thread forms
• Set up a lathe to cut inch external Unified
threads
• Set up an inch lathe to cut metric threads
• Set up a lathe and cut internal threads
• Set up a lathe and cut external Acme
threads

3. 55-3
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

4. 55-4
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

5. 55-5
Thread
Terminology
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6. 55-6
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

7. 55-7
• 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

8. 55-8
• 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)

9. 55-9
• 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

10. 55-10
• 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

11. 55-11
• 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
Copyright © The McGraw-Hill Companies, Inc.
Permission required for reproduction or display.

12. 55-12
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

13. 55-13
Table 55.1
ISO metric pitch and diameter
combinations
Nominal Thread Nominal Thread
Diameter Pitch Diameter Pitch
(mm) (mm) (mm) (mm)
1.6 0.35 20 2.5
2 0.4 24 3
2.5 0.45 30 3.5
3 0.5 36 4
3.5 0.6 42 4.5
4 0.7 48 5
5 0.8 56 5.5
Portion of table taken
from textbook

14. 55-14
ISO Metric Thread
• 60º included angle, crest = 0.125 times pitch
D (depth of thread) is 0.6143 times pitch
Root is 1/4th
of pitch,
Flat on root (FR) wider than crest (FC)
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Permission required for reproduction or display.

15. 55-15
ISO Metric Thread
x
.250
x
.125
x
54127
.
0
(external)
P
FR
P
FC
P
D



Copyright © The McGraw-Hill Companies, Inc.
Permission required for reproduction or display.

16. 55-16
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

17. 55-17
American National Standard Thread
N
P
F
N
P
D
.125
or
x
.125
.6134
or
x
6134
.


Copyright © The McGraw-Hill Companies, Inc.
Permission required for reproduction or display.

18. 55-18
British Standard Whitwork
(BSW) Thread
• Application is same
as for American
National form thread
N
P
R
N
P
D
.1373
or
x
.1373
.6403
or
x
6403
.


Copyright © The McGraw-Hill Companies, Inc.
Permission required for reproduction or display.

19. 55-19
Unified Thread
• Developed by U.S., Britain, and Canada for
standardized thread system
• Combination of British Standard Whitworth and
American National Standard Thread
Copyright © The McGraw-Hill Companies, Inc.
Permission required for reproduction or display.

20. 55-20
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




Copyright © The McGraw-Hill Companies, Inc.
Permission required for reproduction or display.

21. 55-21
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)
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Permission required for reproduction or display.

22. 55-22
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
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23. 55-23
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
Copyright © The McGraw-Hill Companies, Inc.
Permission required for reproduction or display.

24. 55-24
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)
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25. 55-25
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

26. 55-26
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.

27. 55-27
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
Maximum pitch diameter of the
external thread (2A) = .9168 in.
Minimum pitch diameter of the
external thread (2A) = .9100 in.
Tolerance = .0068 in.
The tolerance for a 1 in.—8 UNC Class 2A thread is:

28. 55-28
Limits
• Maximum and minimum dimensions of part
Maximum pitch diameter of the
external thread (2A) = .9168 in..
Minimum pitch diameter of the
external thread (2A) = .9100 in.
The limits for a 1 in.—8 UNC Class 2A thread are:

29. 55-29
ISO Metric Tolerances and Allowances
• ISO metric screw thread tolerance system provides for
allowances and tolerances defined by tolerance grades,
tolerance positions, and tolerance classes
• Tolerance grades specified numerically
– Medium tolerance indicated by number 6, number below 6
indicates finer tolerance and number above 6 indicates greater
tolerance
– Tolerance for thread at pitch line and major diameter may be
shown on drawing using the following symbols:
External threads:
e indicates large allowance
g indicates small allowance
h indicates no allowance
Internal threads:
G indicates small allowance
H indicates no allowance

30. 55-30
Tolerance Example:
An external metric thread may be designated as follows:
Pitch Outside
Nominal Dia. Dia.
Metric Size Pitch Tolerance Tolerance
M 6 X 0.75 - 5g 6g
The thread fit between mating parts is indicated by
internal thread designation followed by the external
thread tolerance:
M 20 X 2 - 6H/5g 6g

31. 55-31
Symbols Used to Indicate
Allowance
• For external threads:
– e indicates a large allowance
– g indicates a small allowance
– h indicates no allowance
• For internal threads:
– G indicates a small allowance
– H indicates no allowance

32. 55-32
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
• Classes 2A and 2B
– Used for most commercial fasteners
– Medium or free fit
• Classes 3A and 3B
– Used where more accurate fit and lead required
– No allowance provided

33. 55-33
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

34. 55-34
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

35. 55-35
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

36. 55-36
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

37. 55-37
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
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Permission required for reproduction or display.

38. 55-38
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

39. 55-39
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

40. 55-40
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

41. 55-41
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

42. 55-42
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

43. 55-43
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

44. 55-44
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

45. 55-45
When tool is fed in at 29º, most of the cutting
is done by the leading edge of toolbit.
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46. 55-46
Table 55.3: Depth setting for cutting
60° ISO
metric threads
Compound Rest Setting
Pitch (mm)
(mm) 0° 30° 29°
0.35 0.19 0.21 0.21
0.4 0.21 0.25 0.24
0.45 0.24 0.28 0.27
0.5 0.27 0.31 0.31
0.6 0.32 0.37 0.37
0.7 0.37 0.43 0.43
0.8 0.43 0.5 0.49
Portion of table taken
from textbook

47. 55-47
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

48. 55-48
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

49. 55-49
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

50. 55-50
To Reset a Threading Tool
• Must reset when need to remove partly
threaded work from lathe, tool removed for
regrinding, or work slips under lathe dog
Procedure
1. Set up lathe and work for thread cutting
2. Start lathe, toolbit clear of work, engage
split-nut lever on correct line
3. Allow carriage to travel until toolbit
opposite any portion of unfinished thread

51. 55-51
4. Stop lathe, leaving split-nut lever engaged
5. Feed toolbit into thread groove using only
compound rest and crossfeed handles until
right-hand edge of toolbit touches rear side
of thread
6. Set crossfeed graduated collar to zero
7. Back out threading tool using crossfeed
handle, disengage split-nut lever, and
move carriage until toolbit clears start of
thread

52. 55-52
8. Set crossfeed handle back to zero and take
trial cut without setting compound rest
9. Set depth of cut using compound rest
handle and finish thread to required depth

53. 55-53
To Convert an Inch-Designed
Lathe to Metric Threading
• Metric threads may be cut on standard quick-
change gear lathe by using a pair of change gears
having 50 and 127 teeth respectively. Lead screw
has inch dimensions so necessary to convert pitch
in millimeters to centimeters and then into threads
per inch
1 in. = 2.54 cm which gives ration
1:2.54
teeth
127
teeth
50
50
50
x
54
.
2
1

(spindle or drive gear)
(lead screw)

54. 55-54
Procedure to Cut a 2-mm Metric Thread on
Standard Quick-Change Gear Lathe
1. Mount the 127-tooth gear on lead screw
2. Mount the 50-tooth gear on spindle
3. Convert the 2-mm pitch to threads per
centimeter:
cm
P
cm
mm
thread/
5
2
10
1
10



4. Set quick-change gearbox to 5 tpi

55. 55-55
5. Set up lathe for thread cutting
6. Take light trial cut
7. Reverse spindle rotation until cutting tool
has just cleared start of threaded section
8. Check thread with metric screw pitch gage
9. Cut thread to required depth
Note: Never disengage the split nut until
the thread has been cut to depth.

56. 55-56
Procedure to Cut
a Left-Hand Thread (60º)
• Basically same as for right-hand threads,
with few exceptions:
1. Set lathe speed and quick-change gearbox
for pitch of thread to be cut
2. Engage feed-direction lever so that lead
screw will revolve in opposite direction to
that for right-hand thread

57. 55-57
3. Set compound rest to 29º to the LEFT
4. Set up left-hand threading tool and square
it with work
5. Cut groove at left end of section to be
threaded
• Gives cutting tool starting point
6. Proceed to cut thread to same dimensions
as for right-hand thread

58. 55-58
Cutting a Thread on
a Tapered Section
• Use same setup as for regular thread cutting
• Most important that threading tool be set at
90º to axis of work
– Do NOT set it square with tapered surface

59. 55-59
Common Methods of
Measuring Threads
1. Thread ring gage
2. Thread plug gage
3. Thread snap gage
4. Screw thread micrometer
5. Optical comparator
6. Three-wire method

60. 55-60
Three-Wire Method of
Measuring Threads
• Recommended by Bureau of Standards and
National Screw thread Commission
• Three wires of equal diameter placed in thread,
two on one side and one on other side
– Wire used should be hardened and lapped to three times
accuracy of thread to be inspected
• Standard micrometer used to measure distance
over wires (M)
• Different sizes and pitches of threads require
different sizes of wires

61. 55-61
The Three-Wire Method of
Measuring 60º Threads
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Permission required for reproduction or display.

62. 55-62
To Calculate the
Measurement over the Wires
N
G
D
M
5155
.
1
3 


where M = measurement over the wires
D = major diameter of the thread
G = diameter of the wire size used
N = number of tpi
Any of the following formulas can be used to calculate G:
P
N
P
N
P
N
.505
or
.505
ire
Smallest w
.57735
or
.57735
wire
size
-
Best
1.010
or
010
.
1
re
Largest wi




63. 55-63
Multiple Threads
• Used when necessary to obtain increase in lead and
deep, coarse thread cannot be cut
• May be double, triple or quadruple, depending on
number of starts around periphery of work
• Pitch: distance from point on one thread to
corresponding point on next thread
• Lead: distance nut advances lengthwise in one
complete revolution
– Single-start: pitch and lead equal
– Double-start: lead twice the pitch
– Triple-start: lead three times pitch

64. 55-64
Single Thread
Double Thread
Triple Thread
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65. 55-65
Multiple Threads May
be Cut on a Lathe
1. Using accurately slotted driveplate or
faceplate
2. Disengaging intermediate gear of end gear
train and rotating spindle desired amount
3. Using thread-chasing dial
• Only for double-start threads with odd-number
lead

66. 55-66
Procedure to Cut an 8-tpi
Double Thread
1. Set up lathe and cutting tool as for cutting
single-start thread
2. Set quick-change gearbox to 4 tpi
3. Cut first thread to half depth required for 4 tpi
4. Leave crossfeed handle set to depth of
thread and not reading on compound rest
graduated collar
5. Withdraw threading tool from work using
compound rest handle

67. 55-67
6. Revolve work exactly ½ turn
• Remove work from lathe with lathe dog
attached
• Replace work in lathe with tail of dog in slot
exactly opposite one used for first thread
7. Reset crossfeed handle to same position as
when cutting first thread
8. Cut second thread, feeding compound rest
handle until graduated collar at same
setting as for first thread

68. 55-68
Thread-Chasing Dial Method of
Cutting Multiple Threads
• Double-start threads with odd-numbered
lead may be cut using thread-chasing dial
1. Take one cut on thread by engaging split
nut at numbered line on chasing dial
2. Without changing depth of cut, take
another cut at unnumbered line on chasing
dial (second thread will be exactly in
middle of first thread)
3. Continue cutting thread to depth, taking
two passes for every depth-of-cut setting

69. 55-69
Square Threads
• Found in vise screws,
jacks, and other devices
where maximum power
transmission required
• Square threading tool
looks like short cutting-off
tool
• Both sides of square
threading tool must be
ground at angle to
conform to helix angle
of thread
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Permission required for reproduction or display.

70. 55-70
Square Threading Tool
• Helix angle of thread (angle of square threading
tool) depends on two factors:
– Changes for each different lead on given diameter
(greater lead, greater angle)
– Changes for each different diameter of thread for given
lead (larger diameter, smaller angle)
Copyright © The McGraw-Hill Companies, Inc.
Permission required for reproduction or display.

71. 55-71
To Calculate the Helix Angles of the
Leading and Following Sides of a
Square Thread
diameter
major
of
nce
circumfere
thread
of
lead
angle
following
Tan
diameter
minor
of
nce
circumfere
thread
of
lead
angle
leading
Tan



72. 55-72
Clearance
• Square toolbit must be
provided with approximately
1º clearance on each side
– Makes it thinner at bottom
• For leading side of tool
– Add 1º to calculated helix
angle
• On following side
– Subtract 1º from calculated
angle
Copyright © The McGraw-Hill Companies, Inc.
Permission required for reproduction or display.

73. 55-73
Procedure to Cut Square thread
1. Grind threading tool to proper leading and
following angles
• Width of tool should be ~.002 in. wider than
thread groove
2. Align lathe centers and mount work
3. Set quick-change gearbox for required
number of tpi
4. Set compound rest at 30º to right, which
will provide side movement if necessary to
reset cutting tool

74. 55-74
5. Set threading tool square with work and
center
6. Cut right-hand end of work to minor
diameter for approximately .060 in. long
7. If work permits, cut recess at end of thread
to minor diameter
8. Calculate single depth of thread
N
500
.
9. Start lathe and just touch tool to work
diameter
10. Set crossfeed graduated collar to zero

75. 55-75
11. Set .003 in. depth of cut with crossfeed
screw and take trial cut
12. Check thread with thread pitch gage
13. Apply cutting fluid and cut thread to
depth, moving crossfeed in from .002
to .010 in. for each cut
• Depth of cut will depend on thread size and
nature of workpiece
Note: Since thread sides are square, all
cuts must be set using crossfeed screw

76. 55-76
Acme Thread
• Gradually replacing square thread because
stronger and easier to cut with taps and dies
• Used extensively for lead screws because
29º angle formed by its sides allows split nut
to be engaged during thread cutting
• Provided with .010-in. clearance for both
crest and root on all sizes of threads

77. 55-77
Procedure to Cut an Acme Thread
1. Grind toolbit to fit
end of Acme thread gage
2. Grind point
of tool flat until
it fits into slots
of gage
• Indicates number
of threads per
inch to be cut
Copyright © The McGraw-Hill Companies, Inc.
Permission required for reproduction or display.

78. 55-78
3. Set quick-change gearbox to required
number of threads per inch
4. Set compound rest 14 ½º to right
5. Set Acme threading tool on center and
square it with work using gage
6. At right-hand end of work, cut
section .060 in. long to minor diameter
7. Cut thread to proper depth by feeding
cutting tool, using compound rest

79. 55-79
Measuring Acme Threads
One Wire Method
• Single wire or pin of correct diameter placed in
thread groove and measured with micrometer
• Thread correct size when micrometer reading over
wire is same as major diameter
of thread and wire is tight
in the thread
Diameter of wire to be
used can be calculated
as follows:
Wire diameter = .4872 x pitch
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Permission required for reproduction or display.

80. 55-80
Internal Threads
• Cutting threads in a hole
– Operation performed on work held in chuck
or collet or mounted on faceplate
– Threading tool similar to boring toolbit
except shape ground to form of thread to be
cut
Procedure
1. Calculate tap drill size of thread
N
1
-
diameter
major
size
drill
Tap 

81. 55-81
2. Mount work to be threaded in chuck or
collet or faceplate
3. Drill hole approximately 1⁄16 in. smaller
than tap drill size in workpiece
4. Mount boring tool in lathe and bore hole to
tap drill size
5. Recess start of hole to major diameter of
thread for .060-in. length
6. If thread does not go through workpiece, a
recess should be cut at end of thread to
major diameter; recess should be wide
enough to allow threading tool to “run out”
and permit time to disengage split-nut lever

82. 55-82
The compound rest is set at 29º to the left
for cutting right-hand internal threads.
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Permission required for reproduction or display.

83. 55-83
7. Set compound rest at 29° to left, to right for
left-hand threads
8. Mount threading toolbit into boring bar and
set it to center
9. Square threading tool with thread center gage
10. Place mark on boring bar, measuring from
threading tool, to indicate length of hole to be
threaded
11. Start lathe and turn crossfeed handle out until
threading tool just scratches internal diameter

84. 55-84
7. Set crossfeed graduated collar to zero
8. Set .003-in. depth of cut by feeding
compound rest out and take trial cut
9. At end of each cut on internal thread,
disengage split-nut lever and feed crossfeed
handle in to clear thread
10. Clear threading tool from hole and check
pitch of thread
11. Return crossfeed handle back to zero and
set depth of cut by turning compound rest
out desired amount
12. Cut thread to depth; check fit with a screw
or threaded plug gage