CNC Programming & Machine Operation 3 — Questions and Answers
Question 1: What is the purpose of the M03 command in a CNC program?
- Stop the spindle
- Start the spindle in a clockwise direction (Correct answer)
- Start the spindle in a counterclockwise direction
- Activate the coolant system
Correct answer: Start the spindle in a clockwise direction
M03 starts the spindle in the clockwise (forward) direction, which is the standard direction for most milling and turning operations.
Question 2: Which M-code is used to activate flood coolant in most CNC controllers?
- M06
- M07
- M08 (Correct answer)
- M09
Correct answer: M08
M08 activates flood coolant, while M07 activates mist coolant, and M09 turns all coolant off.
Question 3: A programmer writes 'S1200 M03' in a CNC block. What does the S-word value represent?
- Feed rate in inches per minute
- Spindle speed in RPM (Correct answer)
- Step-over amount in thousandths of an inch
- Surface footage per minute directly
Correct answer: Spindle speed in RPM
The S-word sets the spindle speed in revolutions per minute (RPM) when the machine is in direct RPM mode.
Question 4: What does G96 mode do in CNC turning?
- Sets constant feed rate in inches per revolution
- Activates constant surface speed (CSS) control (Correct answer)
- Cancels all speed and feed overrides
- Programs spindle speed as a percentage of maximum RPM
Correct answer: Activates constant surface speed (CSS) control
G96 activates Constant Surface Speed mode, automatically adjusting RPM as the tool moves to maintain a consistent surface speed.
Question 5: When using G97 in a CNC lathe program, what is being commanded?
- Constant surface speed mode
- Direct RPM spindle speed mode (Correct answer)
- Feed rate in surface feet per minute
- Spindle orientation for tool change
Correct answer: Direct RPM spindle speed mode
G97 sets the spindle to direct RPM mode, canceling any G96 constant surface speed that may have been active.
Question 6: In CNC turning, what does the address 'F0.012' typically specify when programmed in feed-per-revolution mode?
- Feed rate of 0.012 inches per minute
- Feed rate of 0.012 inches per revolution of the spindle (Correct answer)
- Depth of cut of 0.012 inches
- Tool nose radius of 0.012 inches
Correct answer: Feed rate of 0.012 inches per revolution of the spindle
In feed-per-revolution mode (G99), the F-word specifies how far the tool advances per spindle revolution, directly controlling chip thickness.
Question 7: What is the function of the M30 code at the end of a CNC program?
- Pause the program and wait for operator input
- End the program and reset the control to the beginning (Correct answer)
- Stop the spindle only and leave the program active
- Execute a subprogram call and return
Correct answer: End the program and reset the control to the beginning
M30 ends the program, stops the spindle and coolant, and rewinds/resets the control to the program start for the next cycle.
CNC Programming & Machine Operation 3
What is the purpose of the M03 command in a CNC program?