Threading on a lathe using a proximity stop which is integrated into the VFD to control the stopping position of the lathe. The proximity sensor position is set by the micrometer stop, and the stopping position repeatability is ~0.0004" or better even at high feed rates.

In this example I am cutting a 3/8-24 thread in oil hard drill rod with a Dorian thread cutting insert. When treading a 0.1" relief grove is cut to approximately the depth of the final thread, the thread cutting insert is placed in the center of the relief and the cutter insert point advanced to the depth of the final thread cut. This is then used to set the lathe proximity carriage stop position, the tool post slide dial is set to 0 (the position of the cutter is expected to be in on the final cutting pass). The lathe cross slide is locked, and only the tool post slide is moved from this point forward.

When threading there is no need to disengage the half nut for each pass, at the end of each pass the cutter head is backed out with the tool post slide, the machined reversed by engaging a proximity bypass button, and then the tool post slide advanced to the next cutting depth and the next pass is taken. It is easy to cut a full thread in about 2 minutes with high RPMs and with no worries.

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