CNC Cutting Tool Geometry & Selection 3 — Questions and Answers
Question 1: What does ISO insert designation 'C' in the shape position indicate?
- 80-degree diamond shape (Correct answer)
- Round insert
- Trigon (120-degree triangle)
- Square insert
Correct answer: 80-degree diamond shape
In the ISO insert identification system, 'C' designates an 80-degree rhombic (diamond) insert shape.
Question 2: Which coating is most commonly applied to carbide inserts to improve wear resistance at high temperatures?
- Titanium Nitride (TiN)
- Titanium Carbonitride (TiCN)
- Titanium Aluminum Nitride (TiAlN) (Correct answer)
- Diamond-like Carbon (DLC)
Correct answer: Titanium Aluminum Nitride (TiAlN)
TiAlN coatings have excellent oxidation resistance at elevated temperatures, making them the preferred choice for high-speed dry cutting.
Question 3: What is the relief angle (clearance angle) on a cutting tool designed to prevent?
- Chip recutting
- Rubbing of the tool flank against the machined surface (Correct answer)
- Built-up edge formation
- Excessive cutting forces
Correct answer: Rubbing of the tool flank against the machined surface
The relief angle provides clearance between the tool flank and the workpiece, preventing the tool body from rubbing against the just-machined surface.
Question 4: A drill with a 118-degree point angle is considered standard. A 135-degree point angle is used for:
- Soft materials like plastic
- Hard materials and self-centering applications (Correct answer)
- Deep hole drilling
- Thin sheet metal only
Correct answer: Hard materials and self-centering applications
The 135-degree split-point drill is designed for harder materials and provides better self-centering without a center punch.
Question 5: Which cutting tool material has the highest hardness but lowest toughness?
- Carbide
- Ceramic
- Polycrystalline Diamond (PCD) (Correct answer)
- Cubic Boron Nitride (CBN)
Correct answer: Polycrystalline Diamond (PCD)
PCD is the hardest cutting tool material but is very brittle and requires vibration-free conditions to avoid fracture.
Question 6: In turning, the 'side cutting edge angle' (SCEA) primarily influences:
- Surface finish and radial cutting force
- Axial cutting force and tool life in interrupted cuts
- Depth of cut capability
- Chip thickness and feed force (Correct answer)
Correct answer: Chip thickness and feed force
The SCEA controls the chip thickness relative to the feed per revolution and affects the axial (feed) force component.
Question 7: What distinguishes a roughing end mill from a standard end mill?
- It has more flutes for better finish
- It has serrated or wavy cutting edges to break chips into smaller segments (Correct answer)
- It is made of HSS instead of carbide
- It has a larger helix angle
Correct answer: It has serrated or wavy cutting edges to break chips into smaller segments
Roughing end mills (corncob mills) have serrated edges that divide chips into smaller pieces, reducing cutting forces and allowing heavier material removal rates.
CNC Cutting Tool Geometry & Selection 3
What does ISO insert designation 'C' in the shape position indicate?