4. Cutting Screw Threads
• Design Considerations for Screw-Thread Cutting
– Should allow for the termination of threads before
they reach a shoulder
– Eliminate shallow, blind tapped hole
– Chamfers should be specified at the ends
– Threaded sections should not be interrupted with
slots, holes, or other discontinuities
– Use standard tooling for threads
– Operations should be completed in one step
5. Procedure to Set Up a Lathe for Threading (Screw
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
6. 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
6. Set toolbit at right angles to work, using thread
center gage
7. Arrange apron controls to allow split-nut lever to
be engaged
7. Procedure to cut a Screw 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
8. 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
9. 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
10. 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
11.
12.
13.
14. 14
Thread milling cutters
• single-form cutter – tilted at the helix angle of the thread, then
rotating cutter moved in parallel way with the axis of the
simultaneously rotating workpiece
• multiple-form cutter – set in parallel with the axis of the workpiece –
the thread is completed in one revolution of the workpiece
27. Gear Errors
• Adjacent Pitch Error
• Cumulative Pitch Error
• Profile Error
• The tooth to tooth composite error - Single Flank
• The total composite error - Single Flank
• The tooth composite error - Double Flank
• The total composite error - Double Flank
• The tooth thickness Error
• Cyclic Error
• Run Out
28. • Radial run out
• Eccentricity
• Axial run-Out
• Undulation
• The tooth alignment error
