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

A good milling cutter should possess the following characteristics:

• High Abrasive Resistance: The cutter must maintain its cutting edge under wear and tear for prolonged periods.

• Red Hardness: The hardness of the cutting edge should not significantly be affected by heat generated during machining.

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

1. Set Up: Turn the part to be threaded to the major diameter of the thread.
2. Angle Setting: Set the compound slide to 30 degrees to the right.
3. Tool Positioning: Accurately set the tool post.
4. Gear Check: Check the index plate of the quick-change gearbox for necessary thread pitch settings.
5. Starting the Process: Start the lathe and set it to touch the workpiece.
6. Zeroing: Set dial to zero on the cross feed and compound slide.
7. First Cut: Move the cutting tool a short distance off to clear the end of the workpiece and feed the compound slide 0.05 mm inward to initiate cutting.
8. Using the Half-Nuts: Engage half-nuts in the correct line on the chasing dial to begin the thread cutting process.
9. Retracting for Check: Withdraw the cutting tool and check if the thread pitch is correct after completing the first cut.
10. Successive Cuts: Repeat with successive cuts until the thread is fully complete.

The types of milling cutters that can be used to machine the gear include:

• Form Cutters: For cutting specific shapes such as gears
• Profile Cutters: Used for contouring and following specific profiles.

To calculate the indexing needed for 33 teeth:

The number of turns required is given by:

ext{Number of turns} = rac{1}{ ext{Number of teeth}} = rac{1}{33}

You will complete 1 full turn and then move to 7 holes in a 33 hole-circle for each tooth.

The parts of the dividing head are labeled as follows:

• A: Side and face milling cutters
• B: Vice fixed jaw
• C: Work piece
• D: Collars and spacers
• E: Work holding device
• F: Parallels
• G: Indexing worm
• H: Rotary table

The parts labelled on the screw thread are:

• A: Major/Crest diameter
• B: Pitch diameter
• C: Minor or Root diameter