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

Procedure to Set Up a Lathe for Threading (Screw Thread)

1. Set lathe speed to ¼ speed used for turning2. Set quick-change gearbox for required pitch in

threads per inch or in millimeters3. Engage lead screw4. Secure 60º threading toolbit and check angle

using thread center gage5. Set compound rest at 29º to right; set to left for

left-hand thread

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

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

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

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

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

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

16

CNC thread milling

http://www.misan.cz

External thread millingEnd mill on CNC machining center

18

Threads grinding

Threads grinding• One-profile grinding wheel (Higher pitch values)

• Multiprofile (complete) Gr. Wheel (higher productivity, small ptich only)

20

Radial thread rolling – on a die machine

Methods according the dies function:

a) plunge methodb) traverse method

21

Thread rolling – on a die machine

22

Threading dies• half die →• button die ↓

Thread tapping

1) Drilling2) Countersinking3) Thread – 1st4) Thread – 2nd5) Thread - final

http://www.emugefranken.cz/

Thread taping

25

Thread tapping - manual

Thread Whirling

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

• Radial run out

• Eccentricity

• Axial run-Out

• Undulation

• The tooth alignment error