Hand Wheel on the Lead Screw of the Minilathe
On more than one occasion I've found myself advancing the carriage of the minilathe by hand, instead engaging the half-nuts and allowing the carriage to advance under power. Often, this is simply because I've got the lathe set up for threading and need to turn a small piece before going back to threading, and all that messing around with the back gears simply is more trouble than it's worth.
However using the existing carriage wheel is a pain. It's hard to turn smoothly, and advances the carriage too fast. If only it had a hand wheel on the end of the lead screw...
I made a lead screw extension from a piece of scrap I had, of 1/2" steel rod that was threaded 1/4" on both ends.
It was a simple matter to drill the end of the lead screw 13/64" and tap it 1/4" - in theory. Making the hole concentric and straight, and especially tapping it straight, was a challenge.
Drilling was fairly easy, made especially so by the fact that the lead screw had been center drilled to allow for turning between centers during manufacture. This made starting the 13/64" hole in the center very easy. I drilled the 13/64" hole with a hand drill, and to make sure the hole was straight, I drilled with the lathe running, turning the lead screw fairly fast (it was set up for 20 TPI and I used full speed in low gear) in the opposite direction of the drill bit. This is very important - if you make the hole crooked, you'll be quite unhappy.
Tapping the hole square was more challenging. I started by making a pointer, turning down a piece of 1/4" drill rod to fit the hole, and turning the other end to a point. I stuck this into the hole and turned the lathe back on. It was very close to perfect, turning with very little wobble, and a few taps with a small hammer took care of that. Using the point of the piece, I marked a scrap piece of 2x4, and traced the base of the scrap on the table surface. After removing the piece, I returned the scrap piece of 2x4 to the same location, and the mark I had made on it served as an alighnment aid in getting the tap in straight.
In retrospect, there has to be a better way - maybe drilling the 2x4 scrap for a tap guide - because even with this aid, I wasn't able to get the threads perfectly square. I came pretty close, though.
After screwing the end of the extension into the hole, I found that the hole in the lead screw mounting bracket is a bit under 1/2", so I couldn't tighten the 1/2" diameter extension down against the lead screw. I turned a small shoulder onto the end so the rod would seat tightly against the end of the rod without binding. After seating it solidly, the extension wobbled a bit (those damn drunken threads), but a few hammer-taps straightened it out nicely.
I needed a hand wheel. Not having one, I decided to swipe the tailstock hand wheel (I can't think of a time you'll want to use both the lead screw hand wheel and the tailstock hand wheel at the same time). which is held on with a nut and a grub screw. I removed the extension from the end of the lead screw and turned the outside end of it down to fit the tailstock hand wheel. I filed a small flat for the grub screw.
Lead Screw Extension
I probably should have shortened the extension while I was at it. It's rather longer than it needs to be. I may still go back and do that.
Firmly tightening the 1/2" rod to the lead screw is important, or you'll unscrew it when you try to advance the carriage. This required holding the end of the lead screw in a pair of pliers, protected by a thin sheet of aluminum. Do this carefully to avoid damaging the lead screw threads, and do it at the very end where the carriage can't reach anyway. There is probably a better way to do this - I think the headstock end of the lead screw has an unthreaded section inside the control box, but I didn't feel like removing the control box to see. I thought about jamming the gears with a piece of wood to hold the lead screw still, but I'd rather not risk damaging the gears. Locktite will help.
Whenever the lathe is running and the back gears are engaged, the hand wheel spins. This could be dangerous, to both the operator and the lathe, if something should get tangled with it. Fortunately, it's easy to loosen the grub screw and remove the hand wheel - something you'll need to do if you want to use the tailstock ram anyway.
The LittleMachineShop.com sells replacement parts for the Minilathe, so you can buy an extra tailstock hand wheel for $12.90 (part number 1380, $7.95 - you'll also need the handle, part number 1381, $4.95) if you don't want to swap one back and forth.
© 2003 W. E. Johns