CNC Machine 3 — Questions and Answers
Question 1: What does 'spindle runout' measure on a CNC machine?
- The distance the spindle travels per revolution
- The deviation of the spindle centerline from true rotation (Correct answer)
- The speed difference between programmed and actual RPM
- The thermal expansion of the spindle housing
Correct answer: The deviation of the spindle centerline from true rotation
Spindle runout is the radial deviation of the rotating spindle from its true centerline, which directly affects surface finish and tool life.
Question 2: In a CNC turning center, what is the purpose of the turret?
- It controls workpiece clamping pressure
- It holds multiple cutting tools and indexes them into position (Correct answer)
- It measures workpiece diameter during cutting
- It adjusts coolant flow direction
Correct answer: It holds multiple cutting tools and indexes them into position
The turret on a lathe holds multiple tools and rotates (indexes) to bring each tool into the cutting position without manual changes.
Question 3: What machine feature allows a CNC mill to tilt its spindle or table to machine angled features without repositioning the part?
- 4th or 5th axis (tilt axis) (Correct answer)
- Spindle speed override
- Dual-pallet system
- Through-spindle coolant
Correct answer: 4th or 5th axis (tilt axis)
A 4th or 5th rotary/tilt axis allows the machine to reorient the cutting tool relative to the part for complex angled surfaces in a single setup.
Question 4: Why is machine thermal stability important in precision CNC machining?
- It affects the color of the finished surface
- Thermal expansion changes machine geometry, causing dimensional errors (Correct answer)
- It determines the maximum tool change speed
- It controls the coolant pump flow rate
Correct answer: Thermal expansion changes machine geometry, causing dimensional errors
As machine components heat up, they expand and shift, altering the relative positions of the spindle and workpiece, causing out-of-tolerance parts.
Question 5: What is the role of a CNC machine's servo drive (amplifier)?
- To generate G-code from CAM software
- To convert low-power control signals into high-power motor commands (Correct answer)
- To filter electrical noise from the encoder signal
- To store tool offset data
Correct answer: To convert low-power control signals into high-power motor commands
The servo drive receives position/velocity commands from the controller and amplifies them to supply the power needed to drive the servo motor accurately.
Question 6: A CNC machine's axis position feedback is provided by an encoder. What type of encoder reads position relative to a fixed reference mark?
- Incremental encoder
- Absolute encoder (Correct answer)
- Linear scale
- Resolver
Correct answer: Absolute encoder
An absolute encoder stores the actual position value at every point, so the controller knows the exact location even after a power loss without homing.
Question 7: Which machine component on a CNC lathe holds and rotates the raw workpiece during turning?
- Tailstock
- Chuck (spindle nose) (Correct answer)
- Steady rest
- Carriage
Correct answer: Chuck (spindle nose)
The chuck mounted on the spindle nose grips and rotates the workpiece, while the cutting tool removes material as the part spins.
CNC Machine 3
What does 'spindle runout' measure on a CNC machine?