CNC Safety Standards & Maintenance Practices 2 — Questions and Answers
Question 1: When performing a lockout/tagout (LOTO) procedure on a CNC machine, what is the correct sequence of steps?
- Notify affected employees, shut down equipment, isolate energy sources, apply locks (Correct answer)
- Apply locks first, then shut down, then notify employees
- Isolate energy sources, apply locks, then start the machine to verify
- Shut down, verify zero energy, then notify employees
Correct answer: Notify affected employees, shut down equipment, isolate energy sources, apply locks
LOTO requires notifying affected employees first, then shutting down and isolating all energy sources before applying locks and tags.
Question 2: Which type of fire extinguisher is appropriate for a CNC machine electrical fire?
- Class A
- Class B
- Class C (Correct answer)
- Class D
Correct answer: Class C
Class C extinguishers are designed for electrical fires and use non-conductive agents that won't create shock hazards.
Question 3: What is the primary hazard associated with a worn or damaged CNC machine way cover?
- Increased electrical resistance
- Chip and coolant intrusion damaging linear guides and ball screws (Correct answer)
- Reduced spindle speed accuracy
- Tool changer misalignment
Correct answer: Chip and coolant intrusion damaging linear guides and ball screws
Damaged way covers allow chips and coolant to contact and abrade the precision linear guides and ball screws, causing premature wear.
Question 4: Under OSHA 29 CFR 1910.217, point-of-operation guarding on CNC machining centers must prevent the operator from reaching into the:
- Tool storage carousel
- Control panel area
- Danger zone during the hazardous portion of the machine cycle (Correct answer)
- Coolant reservoir
Correct answer: Danger zone during the hazardous portion of the machine cycle
Point-of-operation guards must physically prevent operator contact with the danger zone during any hazardous part of the machine cycle.
Question 5: A CNC operator notices hydraulic fluid pooling beneath the machine. The correct immediate action is to:
- Continue running the job and report at end of shift
- Stop the machine, place absorbent material, and tag out the machine for maintenance (Correct answer)
- Add fluid to the reservoir and monitor the level
- Increase hydraulic pressure to compensate for the loss
Correct answer: Stop the machine, place absorbent material, and tag out the machine for maintenance
Hydraulic leaks create slip hazards and indicate potential system failure; the machine must be stopped and tagged out for repair.
Question 6: What is the recommended method for removing chips from a CNC machine's work envelope?
- Bare hands while the spindle is stationary
- Compressed air directed at the work zone
- Chip hook or brush with machine in a safe state (Correct answer)
- Shop vacuum without stopping the machine
Correct answer: Chip hook or brush with machine in a safe state
Chip hooks and brushes protect hands from sharp edges, and the machine must be in a safe, non-operating state before chip removal.
Question 7: How often should CNC spindle bearing preload and runout typically be verified as part of preventive maintenance?
- Only when surface finish degrades noticeably
- Per manufacturer's schedule, commonly every 1,000–2,000 operating hours (Correct answer)
- Once per year regardless of usage
- Every shift before production begins
Correct answer: Per manufacturer's schedule, commonly every 1,000–2,000 operating hours
Manufacturer-specified intervals (often 1,000–2,000 hours) ensure bearing condition is caught before it causes dimensional errors or catastrophic failure.
CNC Safety Standards & Maintenance Practices 2
When performing a lockout/tagout (LOTO) procedure on a CNC machine, what is the correct sequence of steps?