Millwright Level 1 Practice Exam

What controls the pitch of a thread cut on a lathe?

1. The tailstock

2. The lead screw

3. The cross-slide

4. The tool post

The correct answer is: The lead screw

The lead screw is the component that plays a crucial role in controlling the pitch of a thread cut on a lathe. It is a long, threaded rod that translates the rotation of the spindle into linear motion for the carriage. When you select a specific pitch for threading, the lead screw engages with the carriage and drives it at a constant rate corresponding to the thread pitch desired. As the lead screw turns, it moves the carriage forward or backward in precise increments, effectively allowing the cutting tool to create threads of a designated pitch. This mechanism is essential for achieving accuracy in the dimensions of the threads being cut, as different pitches require different lead screw settings or gears to match the desired specifications. Other components like the tailstock, cross-slide, and tool post serve different functions in the threading process. The tailstock can aid in supporting the workpiece or holding additional tooling but does not determine thread pitch. The cross-slide controls the depth of the cut, while the tool post holds the cutting tool in place; neither of these components impacts the linear movement driven by the lead screw that ultimately defines the pitch of the thread.