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Anti-backlash nut for cross slide.
- Thread starter agfrvf
- Start date
- Joined
- Jun 7, 2013
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- 10,450
The only time that I consider backlash an issue is when threading, as one must crank extra when withdrawing the tool, it should not effect finish, in any case, other than if the gib is not snug enough.
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- Apr 30, 2015
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- 12,243
That sounds like very loose gibs not a backlash issue. Re-adjust your cross slide gib adjustment screws
Mark
Mark
- Joined
- Jul 2, 2014
- Messages
- 7,594
When the gibs are adjusted to a sliding fit with a bit of resistance, then check your backlash at different places along its travel. If there is more backlash in the middle than at the ends, then that would be in the screw itself, and the maximum improvement you could get with that lead screw in place is the difference between the two most different backlash readings, assuming an (unlikely) perfect nut fit. First, find the problem(s).
- Joined
- Dec 25, 2011
- Messages
- 10,552
The other thing that you should do when facing is to lock the carriage. Tighten the square head bolt on the right side of the carriage just to the left of the threading gauge. Also lock the compound slide by tightening the middle gib adjusting screw. On my 3996, I replaced one of the cross slide and one of the compound gib screws with a T-handle screw. The gib lock for the 10" and 12" milling attachment fits the cross slide. And the one from the 6" milling attachment fits the compound slide. Same locks will work on the 10" and all 12".
To get back to backlash in the cross feed, there are two sources for it. One is backlash or clearance between the cross feed screw and the cross feed nut. The other is end float of the cross feed screw. Before trying to determine or reduce the magnitude of the former, you should address the latter. To do this, first run the cross slide nut off of the end of the cross feed screw and move the slide another quarter inch or so to the rear. Then remove the two screw plugs in top of the carriage dovetail and squirt a few drops of oil into the holes while rotating the screw. Also apply a little oil to the rear of the dial where it runs near or against the front of the bearing. Replace the two screw plugs and run them down flush with the top of the dovetail. Loosen the dial set screw of thumb screw and confirm that the dial rotates freely.
Loosen the special nut retaining the crank. If you haven't done it recently, go ahead and remove all parts and inspect for wear. There are three original versions of how this all goes together, 10" and early 12", late 12" version 1, and late 12" version 2. In some cases it may be advisable to remove the bearing from the front edge of the carriage and face it off flat again. Version 1 and 2 of the late 12" have a flat washer (not in the same location) that may need to be either turned over or replaced. When all is OK, reassemble. By differential adjustments of the hex jam nut, 537-015 Nut or 049-089 Bushing, and the 10D-262 Special Nut, reduce the end float to as near to zero as possible without introducing appreciable drag when you rotate the screw with the crank. When you are satisfied with the adjustment, reaffirm that when loosened, the dial still rotates freely.
In several cases, this procedure has reduced the back lash when everything was reassembled by as much as one-half if you had never done it before.
Pull the cross slide back toward you while rotating the crank CCW. When the screw is fully through the nut, stop and determine the back lash using the installed dial. A new screw and nut would have on the order of 0.005". Assuming that end float is near zero, anything over that is wear in the nut. Crank the cross slide back to where it normally runs and re-check. Any increase over the reading at the end of the screw represents wear on the screw.
What you do from this point is up to you.
To get back to backlash in the cross feed, there are two sources for it. One is backlash or clearance between the cross feed screw and the cross feed nut. The other is end float of the cross feed screw. Before trying to determine or reduce the magnitude of the former, you should address the latter. To do this, first run the cross slide nut off of the end of the cross feed screw and move the slide another quarter inch or so to the rear. Then remove the two screw plugs in top of the carriage dovetail and squirt a few drops of oil into the holes while rotating the screw. Also apply a little oil to the rear of the dial where it runs near or against the front of the bearing. Replace the two screw plugs and run them down flush with the top of the dovetail. Loosen the dial set screw of thumb screw and confirm that the dial rotates freely.
Loosen the special nut retaining the crank. If you haven't done it recently, go ahead and remove all parts and inspect for wear. There are three original versions of how this all goes together, 10" and early 12", late 12" version 1, and late 12" version 2. In some cases it may be advisable to remove the bearing from the front edge of the carriage and face it off flat again. Version 1 and 2 of the late 12" have a flat washer (not in the same location) that may need to be either turned over or replaced. When all is OK, reassemble. By differential adjustments of the hex jam nut, 537-015 Nut or 049-089 Bushing, and the 10D-262 Special Nut, reduce the end float to as near to zero as possible without introducing appreciable drag when you rotate the screw with the crank. When you are satisfied with the adjustment, reaffirm that when loosened, the dial still rotates freely.
In several cases, this procedure has reduced the back lash when everything was reassembled by as much as one-half if you had never done it before.
Pull the cross slide back toward you while rotating the crank CCW. When the screw is fully through the nut, stop and determine the back lash using the installed dial. A new screw and nut would have on the order of 0.005". Assuming that end float is near zero, anything over that is wear in the nut. Crank the cross slide back to where it normally runs and re-check. Any increase over the reading at the end of the screw represents wear on the screw.
What you do from this point is up to you.
Last edited:
- Joined
- Feb 1, 2015
- Messages
- 9,986
Rather than use a double nut on my Atlas/Craftsman 6 x 18, I used an old lead screw nut and a spring to bias the main nut. This arrangement accommodates variable lead screw wear. I now have .002" of backlash in the cross slide. I lose 1" of travel in the cross slide as a result but I can still center the compound pivot under the spindle.
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- Apr 23, 2018
- Messages
- 6,873
In addition to the advice already given, you do have the option of making new feed screws out of acme stock. With new nuts from ebay, I replaced both of mine for about twelve bucks each, and have enough material left over to make two more pair. Made a big difference for my lathe.