CNC Machine 4 — Questions and Answers
Question 1: What is the function of a through-spindle coolant (TSC) system on a CNC machining center?
- To cool the spindle motor windings
- To deliver coolant directly through the tool to the cutting edge (Correct answer)
- To flush chips from the tool changer magazine
- To regulate spindle bearing lubrication
Correct answer: To deliver coolant directly through the tool to the cutting edge
TSC channels high-pressure coolant through the spindle and tool body to the cutting zone, improving chip evacuation and heat removal in deep-hole or difficult-to-reach areas.
Question 2: On a CNC machine, what does 'G28' command the machine to do?
- Set the work coordinate system origin
- Return all axes to the machine home (reference) position (Correct answer)
- Enable cutter radius compensation
- Activate rigid tapping mode
Correct answer: Return all axes to the machine home (reference) position
G28 is the return-to-reference-point command that moves all programmed axes to the machine's home (zero) position.
Question 3: What is the purpose of a CNC machine's pallet changer?
- To automatically sort finished parts by size
- To allow one pallet to be loaded/unloaded while another is being machined (Correct answer)
- To swap tool magazines between jobs
- To rotate the workpiece 180 degrees mid-cycle
Correct answer: To allow one pallet to be loaded/unloaded while another is being machined
A pallet changer improves machine utilization by letting an operator set up the next workpiece on one pallet while the machine cuts the current one.
Question 4: Which axis is typically defined as the axis of rotation of the main spindle in CNC programming standards?
- X-axis
- Y-axis
- Z-axis (Correct answer)
- B-axis
Correct answer: Z-axis
By EIA/ISO convention, the Z-axis is always parallel to the principal spindle axis of rotation in CNC machine tool programming.
Question 5: What causes 'stick-slip' in older CNC machine slideways, and how is it typically corrected?
- Excessive coolant causing corrosion; corrected by switching to oil-based coolant
- Insufficient lubrication causing jerky motion at low feeds; corrected with proper way oil (Correct answer)
- Worn servo motors causing speed fluctuations; corrected by replacing motors
- Misaligned ball screws causing binding; corrected by realignment
Correct answer: Insufficient lubrication causing jerky motion at low feeds; corrected with proper way oil
Stick-slip occurs when dry or poorly lubricated slideways alternate between static and kinetic friction, causing jerky motion especially at slow feed rates.
Question 6: In a CNC machining center, what does the term 'spindle orientation' (M19) accomplish?
- Sets the maximum spindle RPM for the next operation
- Locks the spindle at a specific angular position for tool changes or boring bar indexing (Correct answer)
- Reverses spindle rotation direction
- Synchronizes spindle speed with feed rate
Correct answer: Locks the spindle at a specific angular position for tool changes or boring bar indexing
M19 stops and orients the spindle to a defined angular position, which is required for automatic tool changes or precise tool insertion into a boring bar.
Question 7: What machine feature is 'look-ahead' processing in a CNC controller designed to optimize?
- Tool wear compensation during long programs
- Velocity and acceleration as the machine approaches corners or direction changes (Correct answer)
- Spindle speed fluctuations during threading
- Coolant flow volume based on cut depth
Correct answer: Velocity and acceleration as the machine approaches corners or direction changes
Look-ahead reads multiple blocks ahead in the program so the controller can smoothly decelerate and accelerate around corners without overshooting or losing accuracy.
CNC Machine 4
What is the function of a through-spindle coolant (TSC) system on a CNC machining center?