Only on the lowest of quality machines does the half nut lever get involved in ANYTHING but creating a thread. Better machines are built such that the screw portion of a lead screw is not used for anything else, so it isn't worn unnecessarily. (Many lathes have a slotted lead screw, with the slot driving the mechanisms discussed by Spro. Such mechanism provides feed for the carriage, and often the cross slide. Better quality machines use a separate rod for feeds, so the lead screw isn't even involved).Glenn Brooks wrote:The apron does have a lever on the right side that engages the half nuts for the power feed.
If your lathe has provisions for feeds beyond the use of the half nuts, then, yes, DO NOT ENGAGE BOTH OF THEM, as there would be a conflict of feed rates, resulting in something slipping, or even worse, something getting broken. More modern machines have interlocks that prevent such things from occurring, but they also typically don't have a star knob, but a lever, instead.If I understand you correctly, the star knob also engages the power feed? But Do not engage both.
Then you should try tightening the knob with the spindle of the machine rotating, with the carriage in free space, so if it moves, it won't be obstructed. If tightening the knob does nothing, then something is amiss. Do this with the half nuts open, NOT CLOSED.Still not,sure what the knob actually does.
Harold