I have a Downham Mini Borer (similar/identical to an Elliot) that has no mechanical stop on how far the Z-axis can be wound in the upward direction. This means it's possible to wind it up against some internal, physical limit. That's the situation mine is now in and it doesn't want to wind back the other way.
I imagine the hand-wheel has a worm gear, which turns a wheel around a nut on the vertical threaded bar in the pic below. At the hidden end of the threaded bar, that thread must end, either as an abrupt stop, or as a gradual transition back to the full diameter of the round bar, and it's that that the nut is jammed against. I've tried getting at that nut by removing the automatic feed selector, but the casting that accepts the drive doesn't want to separate from the main head.
Does anybody have any experience of this phenomena on this or a similar borer/mill?