When is the lead screw engaged in a lathe?

Explanation:

Lead Screw Engagement in a Lathe:

• A lead screw is a critical component in a lathe machine, primarily used for transmitting motion to the carriage during machining operations. Its engagement depends on the type of operation being performed. The lead screw is specifically utilized during thread-cutting operations to ensure precise and synchronized motion between the workpiece and the cutting tool. This synchronization is essential for creating accurate threads with consistent pitch.
• In a lathe, the lead screw is engaged by a mechanism called the half-nut, which locks onto the lead screw and allows the carriage to move at the same rate as the rotation of the spindle. This precise movement ensures that the cutting tool traces the desired helical path on the workpiece, which is a fundamental requirement for thread cutting.

Why is the Lead Screw Only Used for Thread-Cutting Operations?

• The lead screw is designed with a specific pitch and thread profile that matches the requirements of thread-cutting operations. Unlike the feed rod, which is used for general-purpose feeding of the carriage during turning, facing, or knurling operations, the lead screw ensures the exact pitch of the thread being cut. Using the lead screw for other operations, such as turning or facing, would result in excessive wear and tear on this critical component, as it is not designed for continuous or general-purpose motion transmission.