Question 41 QMED05 - Machinist-Pump Technician

The Correct Answer is D. ### Why Option D ("stop the lathe") is Correct When lathe centers begin to squeal, it is a critical indication that the two centers (the headstock center and the tailstock center) are rubbing severely against the workpiece, which is generating excessive friction and heat. This usually means the tailstock center is overtightened or the lubrication has failed entirely. Continuing to run the lathe risks immediate and serious damage to the equipment, the workpiece, and potentially the operator: 1. **Damage Prevention:** High friction generates extreme heat, which can soften, score, or weld the metal on both the workpiece center hole and the center point itself. Stopping immediately minimizes this irreversible damage. 2. **Diagnosis and Correction:** You cannot safely diagnose or fix the underlying issue (such as inadequate lubrication or improper tension) while the machine is running. The first and safest step is always to stop the motion, inspect the setup, loosen the tailstock, check the lubrication, and readjust the tension before resuming operations. ### Why Other Options Are Incorrect **A) run the lathe at a slower speed:** Running at a slower speed reduces the rotational velocity but does not eliminate the friction and heat being generated by the improperly loaded or unlubricated centers. While it might momentarily reduce the pitch of the squeal, the underlying destructive friction continues to occur, damaging the equipment. **B) lubricate the centers:** Lubrication is the likely ultimate solution, but you cannot effectively or safely apply lubricant directly to the interface between the rotating workpiece and the stationary tailstock center while the lathe is running, especially when it is under load and generating a squeal. Attempting this is dangerous, and the friction heat may immediately burn off the new lubricant anyway. The correct procedure requires stopping the machine first. **C) change the cutting bit:** The squealing is caused by a problem with the work-holding method (the centers), not the cutting tool itself. Changing the cutting bit addresses a completely unrelated operational parameter and would not solve the catastrophic friction occurring at the centers.