CNC Cutting Tools and Tooling 2 — Questions and Answers
Question 1: What does SFM stand for in CNC cutting tool calculations?
- Surface Finish Measurement
- Standard Feed per Minute
- Surface Feet per Minute (Correct answer)
- Spindle Feed Multiplier
Correct answer: Surface Feet per Minute
SFM stands for Surface Feet per Minute, a measure of the cutting speed at the tool's cutting edge relative to the workpiece.
Question 2: Using the formula RPM = (SFM × 3.82) / Diameter, what RPM is needed for a 0.5-inch end mill at 600 SFM?
- 2,292 RPM
- 4,584 RPM (Correct answer)
- 1,146 RPM
- 3,600 RPM
Correct answer: 4,584 RPM
RPM = (600 × 3.82) / 0.5 = 2,292 / 0.5 = 4,584 RPM, which is the required spindle speed for this tool and cutting speed.
Question 3: What is the chip load (feed per tooth) for a 4-flute end mill running at 3,000 RPM with a feed rate of 60 IPM?
- 0.005 inches (Correct answer)
- 0.020 inches
- 0.015 inches
- 0.010 inches
Correct answer: 0.005 inches
Chip load = Feed Rate / (RPM × Number of Flutes) = 60 / (3,000 × 4) = 60 / 12,000 = 0.005 inches per tooth.
Question 4: What is the primary function of a drill's point angle?
- To determine spindle speed requirements
- To control the size of the entry chamfer
- To affect how the drill starts and centers itself (Correct answer)
- To set the correct retract height
Correct answer: To affect how the drill starts and centers itself
The drill point angle affects how the drill centers itself on entry and how aggressively it cuts — 118° is standard for general use, 135° for harder materials.
Question 5: Which tool type is specifically designed to enlarge and improve the surface finish of an existing hole?
- Center drill
- Boring bar
- Reamer (Correct answer)
- Counterbore
Correct answer: Reamer
A reamer is designed to slightly enlarge a pre-drilled hole while producing a very precise diameter and superior surface finish.
Question 6: What does the term 'runout' refer to when measuring a cutting tool in a holder?
- The distance the tool extends from the holder
- The deviation of the tool tip from true rotation center (Correct answer)
- The maximum depth of cut the tool can handle
- The feed rate range for the tool
Correct answer: The deviation of the tool tip from true rotation center
Runout is the amount of eccentricity (wobble) of the tool tip as it rotates, measured by a dial indicator — excessive runout reduces tool life and part accuracy.
CNC Cutting Tools and Tooling 2
What does SFM stand for in CNC cutting tool calculations?