As promised, here are some pics of the Unimat headstock alignment guide. Let me emphasize here that this tool is a commercial product made by National Camera, Englewood, CO 80110 and not something made by me. It was bought many, many years ago so I have no idea if the company still exists. That said, it's a simple enough device and any competent hobby machinist could cobble one together in a few hours.
As is obvious from the pictures it clamps across the Unimat drill rod lathe ways and is secured in place by the small thrumb screw. The differential screw mechanism consists of a large hex-headed adjuster nut threaded 28 tpi into the frame. In the center of this adjuster, a small pusher screw is threaded 32 tpi into the adjuster and prevented from rotating by the spring lock visible on the back of the frame in the second photo.
Thus a full rotation of the adjuster will move the pusher by:
1/28 - 1/32 = 1/224 = 0.00446"
so a 1/6 rotation (ie, one flat on the adjuster) will move it 0.00074"
In use, one butts the pusher against the Unimat spindle, takes a test cut on a bit of scrap, measures the amount of taper produced and then makes a correction with the adjuster nut. This process is repeated until the taper is reduced to an acceptable level at which time the lock nut on the top of the frame is used to lock the adjuster in place. Then the next time the headstock is moved, it's a simple matter to drop the unit in place, move the spindle against the pusher, lock in place and Bob's your mother's brother.
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