Having worked in a production shop on Porter-Cable lathes many years ago, I very well remember that the mechanical feed stops supplied with the lathes from the factory did have issues with repeatability. The heavier the cut, and even the duller the tool became in production, the more stress on the feed engagement gear/dog? and the further it would hang on till disengaging. We had to have the same depth cut on each pass to ensure there were no disasters!! I have a homemade stop on the halfnut lever on my Chinese lathe but I don't really trust it. If I was to build an auto feed stop for the feed lever, I would use a micro switch and a solenoid to disengage. We had used a similar system on some Logan lathes, and the disengage point was very stable, an air cylinder was used not a solenoid, but the stop point was very reliable
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