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| Yah metric often means keep the half nut closed unless the lead screw is metric. Then is when you wish for a hand crank on the spindle for a few turns or a good quick drive clutch in a gear head lathe so you can sneak up and easily back up.
Friend of mine has a sturdy Italian lathe that has US style quick change box, but shows all kinds of pitches US, Metric, modular for cutting worm gears, and about 5 others set up by changing the manual change gears and it never has had a threading dial. Just has a quick clutch and gear head to get really slow. It has a separate shaft out of that gear box for the manual change gear drive the turns the same as the hollow spindle.
On my little lathe I made a hand crank to fit in the outside of the spindle hollow shaft. I used a flat piece of steel with a knob on the side, and an expanding concrete anchor bolt in the hollow shaft. It mounts and comes out fairly easily, really handy when cutting a short coarse thread. Like a 2"-4 thread for a spare water cap for my camper that has to stop three or four turns in against the inside of the cap.
Sometimes that crank needs to be on the lead screw instead of the spindle where the pitch is large, like fewer than four to the inch because the change gears and the quick change gear box are often turning the lead screw faster than the spindle and they can't hack that and cut steel with the rapid feed too. Also in that situation the hand crank is easier to turn on the right hand end of the lead screw than on the spindle.
The 50 or 100 to 127 gears are exact. There are other odd ratios that are not as close but close enough.
Gerald J.
Edited by Gerald J. 3/2/2013 21:53
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Units of measure
