Question 45 QMED05 - Machinist-Pump Technician

The Correct Answer is A **Why option A ("stop the lathe rotation") is correct:** Changing spindle speeds on a lathe typically involves moving internal gears within the headstock (the gear train). Attempting to shift these gears while the spindle and the gears are rotating (i.e., while the lathe is running) can cause severe damage to the gear teeth, potentially stripping them, and is extremely dangerous to the operator. Therefore, the absolute first step to safely change the spindle speed is to completely stop the spindle rotation. **Why the other options are incorrect:** * **B) disengage the feed reverse lever:** The feed reverse lever controls the direction of the automatic feed mechanism (carriage movement or thread cutting). While part of safe operation, it is unrelated to the requirement of stopping the physical rotation of the headstock gears necessary for a speed change. * **C) disengage the spindle clutch:** Disengaging the spindle clutch stops the power transmission to the spindle, effectively stopping the rotation (making the rotation stop). However, in many modern lathes, stopping the **lathe rotation** (usually via the main power switch or brake) is a more definite and necessary step before manipulating the internal gears, especially if the lathe lacks a direct clutch or if the shift requires the machine to be fully powered down or braked. More fundamentally, "stopping the rotation" (A) is the *result* that enables the safe shift, regardless of the exact mechanism (clutch or brake) used to achieve it. * **D) engage the feed change lever:** The feed change lever modifies the rate at which the carriage or cross slide moves (the feed rate). This is separate from the spindle speed and has no bearing on the safety procedure for shifting the main spindle gears.