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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.

Downham

Does anybody have any experience of this phenomena on this or a similar borer/mill?

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  • $\begingroup$ Is it the quill or the column that's jammed? Try practicalmachinist.com forums also. $\endgroup$ – GisMofx Dec 22 '15 at 12:49
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In this instance, the issue was as predicted - the wheel/nut driven by the worm connected to the hand wheel had jammed against an internal stop.

The solution I went with begins with removing the conventional nut at the top of the vertical screw pictured. This allows the plate at the top end of the large diameter section to lift off the end of the screw (taking the chuck etc. with it). It only needs to be lifted far enough to expose the top end of the screw. At this point I found a suitably sized nut, drilled it to half an inch and cut/filed a slot in it to accept the Woodruff key. It can then be placed on the end of the screw and used to turn it (clockwise, viewed from above) to release the internal jam. It did not require much torque.

NOTE: There's a near-horizontal linkage that transfers load from an internal counter-weight to make raising the head easier. That needs to be removed to allow the quill to rise higher than normal, but watch out for the tension in the chain when doing that. Take steps to constrain the linkage.

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