CNC Cutting Tool Geometry & Selection 2 — Questions and Answers
Question 1: What does a negative rake angle on a cutting tool indicate?
- The cutting edge is angled away from the workpiece surface (Correct answer)
- The cutting edge is angled toward the workpiece surface
- The tool has no rake angle
- The tool cuts below the centerline
Correct answer: The cutting edge is angled away from the workpiece surface
A negative rake angle means the tool face tilts away from the direction of cut, which strengthens the cutting edge and is suited for hard or interrupted cuts.
Question 2: Which tool material is best suited for high-speed machining of cast iron without coolant?
- High-speed steel (HSS)
- Ceramic (Correct answer)
- Carbon steel
- Cobalt HSS
Correct answer: Ceramic
Ceramic inserts withstand very high temperatures and are ideal for dry, high-speed machining of cast iron due to their thermal stability.
Question 3: The nose radius of a turning insert primarily affects which machining outcome?
- Chip evacuation direction
- Surface finish quality (Correct answer)
- Tool entry angle
- Spindle speed selection
Correct answer: Surface finish quality
A larger nose radius produces a smoother surface finish by spreading the cutting contact over a wider area.
Question 4: What is the purpose of a chip breaker groove on an insert?
- Increase cutting speed capacity
- Curl and break chips to prevent long stringy chips (Correct answer)
- Reduce insert weight
- Improve thermal conductivity
Correct answer: Curl and break chips to prevent long stringy chips
Chip breaker grooves deform the chip as it forms, curling it into manageable pieces that clear the cutting zone safely.
Question 5: When turning stainless steel, which insert grade characteristic is most important?
- High hardness at room temperature
- High toughness and built-up edge resistance (Correct answer)
- Maximum brittleness
- Low thermal conductivity
Correct answer: High toughness and built-up edge resistance
Stainless steel is tough and work-hardens, so inserts need toughness and coatings that resist built-up edge (BUE) formation.
Question 6: In a milling operation, what does the term 'axial depth of cut' refer to?
- How far the cutter extends into the workpiece along the spindle axis (Correct answer)
- The width of material removed in a single pass
- The feed rate per tooth
- The cutter diameter engagement percentage
Correct answer: How far the cutter extends into the workpiece along the spindle axis
Axial depth of cut is the depth measured parallel to the cutter's rotational axis, determining how deep the tool plunges into the material.
Question 7: Which end mill type is preferred for machining aluminum due to chip evacuation?
- 4-flute end mill
- 2-flute end mill (Correct answer)
- 6-flute end mill
- Ball-nose end mill with 4 flutes
Correct answer: 2-flute end mill
2-flute end mills provide larger flute gullets, allowing aluminum chips (which are large and sticky) to evacuate without clogging.
CNC Cutting Tool Geometry & Selection 2
What does a negative rake angle on a cutting tool indicate?