CNC CNC Mill Setup & Operation 2 — Questions and Answers
Question 1: When indicating a vise jaw parallel to the X-axis on a CNC mill, which tool is most commonly used?
- Dead-blow hammer
- Dial test indicator (DTI) (Correct answer)
- Edge finder
- Touch-off probe
Correct answer: Dial test indicator (DTI)
A dial test indicator is swept along the jaw face while adjusting the vise until runout is within tolerance.
Question 2: A CNC milling program calls G43 H02. What does H02 specify?
- The tool diameter offset register 2
- The tool length offset register 2 (Correct answer)
- A canned cycle depth of 0.2 inches
- The second work coordinate system
Correct answer: The tool length offset register 2
G43 activates tool length compensation and H02 selects the value stored in offset register number 2.
Question 3: Which G-code cancels cutter radius compensation (CRC)?
- G40 (Correct answer)
- G41
- G42
- G49
Correct answer: G40
G40 cancels cutter radius compensation, while G41 is left compensation and G42 is right compensation.
Question 4: What is the purpose of a pecking cycle (G83) in CNC milling?
- Mill a pocket using an outward spiral path
- Drill deep holes with periodic chip-clearing retracts (Correct answer)
- Rigid tap a threaded hole
- Bore a hole to a precise diameter
Correct answer: Drill deep holes with periodic chip-clearing retracts
G83 is the deep-hole peck-drilling cycle that retracts to the R-plane between each peck to clear chips and allow coolant penetration.
Question 5: On a Fanuc-style control, what does the address F represent in a milling program?
- Feed rate in inches or mm per minute (or per revolution) (Correct answer)
- Finish allowance in the current axis
- Frequency of the spindle drive
- Number of flutes on the cutter
Correct answer: Feed rate in inches or mm per minute (or per revolution)
The F word specifies feed rate, interpreted as per-minute (G94) or per-revolution (G95) depending on the active feed mode.
Question 6: Which of the following best describes 'climb milling'?
- The cutter rotates opposite to the direction of feed
- The cutter rotates in the same direction as the table feed (Correct answer)
- The cutter is plunged vertically into the workpiece
- The spindle speed increases as depth of cut increases
Correct answer: The cutter rotates in the same direction as the table feed
In climb milling the cutter teeth move in the same direction as the feed, resulting in a chip that starts thick and thins, generally producing better surface finish.
Question 7: What is the function of the 'dry run' mode on a CNC mill control?
- Runs the program with coolant disabled only
- Overrides all feed rates to a rapid-like speed for program verification without cutting (Correct answer)
- Executes only the first block of the program
- Locks the Z-axis to prevent tool plunge
Correct answer: Overrides all feed rates to a rapid-like speed for program verification without cutting
Dry run mode substitutes the programmed feed rates with a manually set rapid-style rate so operators can verify tool paths without engaging the workpiece.
CNC CNC Mill Setup & Operation 2
When indicating a vise jaw parallel to the X-axis on a CNC mill, which tool is most commonly used?