This is a lovely drawing of my Atlas/Craftsman 12" lathe's compound screw and parts.
Now, I intend to replace the 1" dial with a 2" dial so I can see it easier. While I was taking it apart to see how it worked and to remove some backlash, I decided perhaps it could be improved with a bearing.
I'll describe the drawing. You see the compound's screw at the top. One end is acme threaded, the other has normal threads.
The bushing slides over the end of the shaft and is bolted to the compound casting. Note where I've put the black arrow - this shoulder butts up against the bushing. This is what prevents the screw from backing out of the compound. The 3/8" hole in the bushing is a good fit on the compound screw. This bushing prevents the screw from flopping around.
Next, the dial goes on. Note the set screw. I suppose this is how I'm supposed to 'zero' the dial.
Now the 'thin nut' goes on. It's so thin none of my wrenches can tighten it once the handle's on. I need to make a wrench from bar stock I suppose. I believe backlash is removed by tightening this nut up against the shoulder in the screw.
Next the handle and its woodruff key go on.
Finally, the normal nut goes on. I believe tightening this down actually tightens the handle against the thin nut, and thus locks the thin nut.
Now, I'm already going to replace the 1" dial with a 2" dial. While I'm hacking away, is there any reason not to add some real bearings?
1. The shoulder just begs for a bearing of some sort. It rubs against the bushing, and I have to remake the bushing anyway; the dial's 'zero mark' is cast into it. And it will be too small for the larger dial. I could drill the hole in the new bushing a little bigger and install this bronze sleeve bearing. The bearing's flange would rub against the screw's shoulder.
2. The dial rubs directly against the bushing. Since I am making a new dial, and it's 1/2" thick, is there any reason not to sneak a ball thrust bearing in there?
3. I really dislike the setscrew that's on the dial. I'd prefer something without a set screw. My friend's 9x20's dials move easily enough but stay put due to friction. I believe the dial has an inner ring and an outer ring, and an o-ring between them. Anyone know a different snazzy way to accomplish this?
Any other ideas?