CNC Basics 2 — Questions and Answers
Question 1: What does the term 'feed rate' refer to in CNC cutting?
- The speed at which the spindle rotates
- The rate at which the cutting tool advances into the workpiece (Correct answer)
- The depth of each cutting pass
- The tool change frequency
Correct answer: The rate at which the cutting tool advances into the workpiece
Feed rate is the speed at which the cutting tool moves relative to the workpiece, typically expressed in inches per minute (IPM) or millimeters per minute.
Question 2: Which G-code command is used to set absolute positioning mode in CNC programming?
- G90 (Correct answer)
- G91
- G92
- G94
Correct answer: G90
G90 sets the machine to absolute positioning mode, where all coordinates are measured from the origin (work zero).
Question 3: What is the purpose of a coolant in CNC cutting operations?
- To lubricate the machine ways only
- To reduce heat, lubricate the cut, and flush away chips (Correct answer)
- To harden the workpiece surface
- To increase spindle torque
Correct answer: To reduce heat, lubricate the cut, and flush away chips
Coolant simultaneously reduces cutting heat, lubricates the tool-workpiece interface, and evacuates chips from the cutting zone.
Question 4: What is 'climb milling' in CNC machining?
- Milling uphill on an inclined surface
- The cutter rotates in the same direction as the feed (Correct answer)
- The cutter rotates opposite to the feed direction
- Milling at increasing depth per pass
Correct answer: The cutter rotates in the same direction as the feed
In climb milling, the cutter rotates in the same direction as the workpiece feed, which tends to produce a better surface finish and longer tool life.
Question 5: What unit is spindle speed (RPM) typically calculated from when setting up a CNC cut?
- Material hardness and depth of cut
- Cutting speed (SFM or m/min) and tool diameter (Correct answer)
- Feed rate and number of flutes
- Coolant flow rate and chip load
Correct answer: Cutting speed (SFM or m/min) and tool diameter
RPM is derived from the recommended cutting speed (surface feet per minute) and the tool diameter using the formula RPM = (CS × 12) / (π × D).
Question 6: In G-code, what does the M03 command do?
- Stops the spindle
- Starts the spindle clockwise (Correct answer)
- Starts the spindle counterclockwise
- Activates the coolant
Correct answer: Starts the spindle clockwise
M03 starts the spindle in the clockwise (forward) direction and is paired with an S word to set the speed.
Question 7: What is 'depth of cut' (DOC) in CNC milling?
- The total length of the tool path
- How deep the tool engages the workpiece in the axial direction (Correct answer)
- The radial width of the cut
- The distance from the tool tip to the spindle nose
Correct answer: How deep the tool engages the workpiece in the axial direction
Depth of cut (axial DOC) is the measurement of how far the cutter plunges into the workpiece along the spindle axis per pass.
CNC Basics 2
What does the term 'feed rate' refer to in CNC cutting?