5.1 Milling cutters can be divided into two groups: according to design or method of sharpening - NSC Mechanical Technology Fitting and Machining - Question 5 - 2017 - Paper 1

A good milling cutter should have:

1. High Abrasive Resistance: This ensures durability and longevity.
2. Edge Toughness: The cutting edges must retain their hardness and not be adversely affected by heat generated during cutting.

To perform the screw-cutting procedure:

1. Turn the part to be threaded to the major diameter of the thread.
2. Set the compound slide at an angle of 30° to the right and accurately position the tool post.
3. Check the index plate of the quick-change gearbox and adjust the levers for the required thread pitch.
4. Begin the lathe and start the cutting tool against the workpiece while setting the dial to zero on both the cross feed and compound slide.
5. Move the cutter back a short distance, then feed the compound slide inward by 0.05 mm.
6. With the lathe engaged, use half-nuts to thread slowly, feeding until the cut first engages.
7. To verify the depth of the cut, retract the carriage, return to the start, and check thread pitch correctness.
8. Repeat this with successive cuts until the thread is complete.

For machining a gear with thirty-three (33) teeth, Form Cutters or Profile Cutters are suitable options.

To calculate the indexing for 33 teeth:

• Divide 1 full turn (360 degrees) by the number of teeth: ext{Number of turns} = rac{1}{33}
• Therefore, each turn must be divided into 33 holes.

The parts of the dividing head are labeled as follows: A. Side and face milling cutters B. Vice fixed jaw C. Parallels D. Work piece E. Collar and spacers F. Indexing disc G. Rotating handle H. Base

The parts of the screw thread are identified as: A. Major/Crest diameter B. Pitch diameter C. Minor or Root diameter