THREAD CUTTING IN A LATHE

Threads that must be accurate with some turned part must be turned in the lathe at the same setting
used to turn the work. For this work, a proper cutting tool is set up in the tool post, and the lead screw is
geared to the head stock spindle to give the required lead to the thread.

Cutting threads on the engine lathe is usually done when only a few threads are to be cut or when
special forms of threads are necessary. For the operation, the lead screw is revolved at a desired ratio
with the spindle of the lathe through a series of gears. Quick-change gearboxes enable the operator to
produce various pitches of threads, using control levers.

In the thread-cutting operation, the lathe should be set at the correct ratio of feed to speed for the
desired thread to be cut.

Next, the compound is adjusted so the micrometer dial on its collar is at zero. The tool is then brought
into contact with the work piece by adjusting the cross-slide and setting its micrometer dial to zero. All
adjustments for depth of cut can be made from these settings.

It is common practice to use both the cross-slide, and the compound. The tool is backed off the work
piece and the carriage is moved to where the tool is, at a point beyond the end of the work piece. The
cross-slide is then advanced until the micrometer dial reads the same as where the tool was touching
the work piece.

Next, the compound is advanced .002 to .003" and a trial cut is taken. At the end of the cut, the
cross-slide is backed off and the tool returned to its starting point.