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

Two characteristics of a good milling cutter are:

1. High abrasive resistance to withstand wear during milling operations.
2. Edge toughness to prevent chipping or breaking of the cutting edges.

To explain the screw-cutting procedure using the compound-slide method, follow these steps:

1. Turn the part to be threaded to the major diameter of the thread.
2. Set the compound slide at 30° to the right and accurately set the tool in the tool post.
3. Check the index plate of the quick-change gearbox and move the levers for the necessary pitch of the thread.
4. Start the lathe and set the cutting tool to touch the workpiece. Set the dial to zero on the cross feed and compound slide.
5. Move the cutting tool a short distance off to clear the end of the work piece and feed the compound slide 0.05 mm inward.
6. With lathe turning, engage half-nuts in the correct line on the chasing dial, putting the first cut in progress.
7. Withdraw the cutting tool quickly and disengage the half-nut lever return the carriage to the starting point of the thread and check with a gauge if the thread pitch is correct.
8. Repeat with successive cuts until the thread is complete.

The type of milling cutter that can be used to machine the gear is a form cutter or profile cutter.

To calculate the indexing needed for milling 33 teeth:

1. The formula for the number of turns is:

where n is the number of teeth. 2. This means 1 full turn and 7 holes in a 33 hole-circle are needed.

The parts of the dividing head are: A. Side and face milling cutter B. Vice fixed jaw C. Parallels D. Work piece E. Collar and spacers F. Work table G. Indexing head H. Dividing plate.

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