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

Characteristics of a good milling cutter include:

1. High Abrasive Resistance: This ensures that the cutter maintains its sharpness and longevity during the milling process.

2. Red Hardness: The cutter should maintain its hardness even when subjected to high temperatures generated during cutting, preventing wear and deformation.

To perform screw cutting using the compound-slide method:

1. Set Up: Turn the part to be threaded to the major diameter of the thread.
2. Positioning: Set the compound slide at a 30° angle to the right and accurately set the tool in the tool post.
3. Selecting Threads: Check the index plate of the quick-change gearbox and adjust levers for the needed pitch of the thread.
4. Initiating Cutting: Start the lathe and set it to cut the workpiece. Set the dial to zero on the cross feed and compound slide.
5. Cutting Process: Move the cutting tool a short distance off to clear the end of the workpiece, then feed the compound slide 0.05 mm inward.
6. Engaging Half-Nuts: While turning the lathe, engage half-nuts in the correct position to begin the chasing dial.
7. Final Touch: Withdraw the cutting tool and disengage the half-nut lever. Return the carriage to the starting point and check the thread gauge for correctness.
8. Repeat: Continue this process until the full thread is complete.

The types of milling cutters suitable for machining the gear include:

1. Form Cutters.
2. Profile Cutters.

To calculate the indexing needed for 33 teeth,

1. Formula: The number of turns needed can be calculated as:

   egin{align*} ext{Number of Turns} &= rac{1 ext{ Full Turn}}{33 ext{ teeth}} + ext{Holes per half-circle} \ &= rac{1}{33} + 1 ext{ Full Turn = } rac{1}{2} ext{ for 7 holes} \ &= rac{1}{33} + rac{7}{2}
   egin{align*}

   This calculation results in the proper indexing for the mechanical setup.

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: Collars and spacers.
• F: Indexing worm
• G: Handwheel
• H: Tailstock.

The three parts of the screw thread are:

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