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HOW THREADS ARE CUT ON A LATHE

Threads are cut on a lathe with a single-point tool by taking a series of cuts in the same helix of the thread. This is sometimes called chasing a thread.A direct ratio exists between the headstock spindle rotation, the lead screw rotation, and the number of threads on the lead screw. This ratio can be altered by the quick-change gearbox to make a variety of threads.When the half-nuts are clamped on the thread of the lead screw, the carriage will move a given distance for each revolution of the spindle. This distance is the lead of the thread.

HOW THREADS ARE CUT ON A LATHE 299
If the infeed of a thread is made with the cross slide (FigureI-299), equal-sized chips will be formed on both cutting edges of the tool.

HOW THREADS ARE CUT ON A LATHE 300

 

This causes higher tool pressures, which can result in tool breakdown, and sometimes causes tearing of the threads because of insufficient chip clearance. A more accepted practice is to feed in with the compound, which is set at 29 degrees (Figure I-300) toward the right of the operator, for cutting right-hand threads. This ensures a cleaner cutting action than with 30 degrees, with most of the chip taken from the leading edge and a scraping cut from the following edge of the tool.

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