Guys I have finally started to use my my lathe more and more and now found out that I have a little to much play in the cross slide so the nut needs to be replace.I have the 12" Sears 101.28940 and looking in the download section is part #33 537-041 Carriage Slide Nut.I have found a couple on ebay for 35.00 and they are new never been installed.I was wondering if others have replace their carriage slide nut and if that cure the play in the cross slide?There is no side to side movement just towards/backwards from the nut.I watch a Utube while back where a guy replace his and it was just to tight so he had to machine his to get his to fit.Thanks guys for the advice and pointers----kroll
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Carriage Slide Nut Replacement???
- Thread starter Kroll
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I have an Sears/Atlas 6" lathe and replaced the lead screw nut years ago. It will help to take up some of the play but do not expect it to remove all play. There will also be wear in the lead screw and there may be some clearance in the bearing adjustment. The latter can be fixed with an adjustment or shims. To assess the lead screw contribution, move the cross slide to the far inboard position. This is a region where it is least likely that you have wear. Set a dial or test indicator up to measure the slide movement and record the dial readings where you first see the slide move. Check out the center of travel as well as this is probably where most of the wear occurs.
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On the 6" lathe at least, the lead screw nut is held in place by a single flat head screw which also fastens the lead screw cover. Make sure that screw is tight. If it is loose , it contribute to the backlash.
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Kroll,
With a sixteenth inch of movement, if it were all attributable to the nut, you would have virtually no threads left as the thread thickness can't be much more than that. Have you adjusted the cross-feed screw end float? You do that by differential adjustments of the nut that secures the crank and the nut between the crank and the dial. Best done with the carriage nut run off the end of the screw at the rear. And it will be easier to do if you have a thin pattern (tappet) open-end wrench for the nut between the crank and dial, and a box end for the crank nut.
If you do replace the cross feed brass nut, also order a couple of 9-87 Washer, Carriage Slide Nut. These are actually shims. The original illustrated parts lists show it as one round washer, but they are actually rectangular shims. I think that the copy of the parts lists in Downloads have been corrected but if the washer still shows as round, let me know.
Anyway, to properly install the nut, first adjust the screw end float to minimum. Then install the new nut but only run the round head screw down to finger tight. Pull back on the cross slide and start turning the crank until the screw engages the nut, and then retract the carriage until the nut again runs off the screw. Push the carriage and turn the crank until the threads grab, and then about 8 more revolutions of the crank. Loosen the round head screw slightly and then with your fingers carefully tighten it until it just touches the top of the cross slide. Note the position of the slot. With a screwdriver, fully tighten the screw, noting how may turns or fractions of turns the screw makes. The screw is 20 TPI which is 0.050" per turn. Calculate the shim thickness required from this and the number of turns and fractions of turns. Crank the nut back off of the screw, install the shims (if needed), back the nut fully onto the cross feed screw, and fully tighten the round head screw.
With a sixteenth inch of movement, if it were all attributable to the nut, you would have virtually no threads left as the thread thickness can't be much more than that. Have you adjusted the cross-feed screw end float? You do that by differential adjustments of the nut that secures the crank and the nut between the crank and the dial. Best done with the carriage nut run off the end of the screw at the rear. And it will be easier to do if you have a thin pattern (tappet) open-end wrench for the nut between the crank and dial, and a box end for the crank nut.
If you do replace the cross feed brass nut, also order a couple of 9-87 Washer, Carriage Slide Nut. These are actually shims. The original illustrated parts lists show it as one round washer, but they are actually rectangular shims. I think that the copy of the parts lists in Downloads have been corrected but if the washer still shows as round, let me know.
Anyway, to properly install the nut, first adjust the screw end float to minimum. Then install the new nut but only run the round head screw down to finger tight. Pull back on the cross slide and start turning the crank until the screw engages the nut, and then retract the carriage until the nut again runs off the screw. Push the carriage and turn the crank until the threads grab, and then about 8 more revolutions of the crank. Loosen the round head screw slightly and then with your fingers carefully tighten it until it just touches the top of the cross slide. Note the position of the slot. With a screwdriver, fully tighten the screw, noting how may turns or fractions of turns the screw makes. The screw is 20 TPI which is 0.050" per turn. Calculate the shim thickness required from this and the number of turns and fractions of turns. Crank the nut back off of the screw, install the shims (if needed), back the nut fully onto the cross feed screw, and fully tighten the round head screw.
Thank you Robert,I will check into that.I don't remember seeing any shims which means that I lost them I guess.I will have to enlarge the drawings to see if the shims are round or rectangular and just to double check to see if their there or not.If I do need some shims,where can they be purchase from or is this something that I will have to try and make?
OK Robert,I think I understand now and I see its part#35 (9-81).I think I will take it apart again and just go through it.Thanks for taking the time and doing a fantastic download section
OK Robert,I think I understand now and I see its part#35 (9-81).I think I will take it apart again and just go through it.Thanks for taking the time and doing a fantastic download section
Last edited:
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On the 9", 10" and 12", the screw holding the cross feed nut is a separate part and is a round head slotted screw.
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Kroll,
You're welcome.
The shim could be stuck to the bottom of the cross slide. Or it might not have been there to begin with. My 3996 didn't have one originally. But when I installed a new nut last year, the new nut needed one.
You can buy them from Clausing or make them. I forget what the thickness is but if you find that you need one and decide to make it, determine what thickness you need and buy the nearest standard shim stock.
I forgot to add earlier that while you are determining what thickness you need, when you have the carriage in position over tighten the feed screw thrust bearing adjustment snugly.. If it is a little or a lot loose, the screw will droop and move around.
You're welcome.
The shim could be stuck to the bottom of the cross slide. Or it might not have been there to begin with. My 3996 didn't have one originally. But when I installed a new nut last year, the new nut needed one.
You can buy them from Clausing or make them. I forget what the thickness is but if you find that you need one and decide to make it, determine what thickness you need and buy the nearest standard shim stock.
I forgot to add earlier that while you are determining what thickness you need, when you have the carriage in position over tighten the feed screw thrust bearing adjustment snugly.. If it is a little or a lot loose, the screw will droop and move around.
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Was awaiting my new $35 cross slide nut when I first read your post. Got it yesterday, installed it today. Vastly Improved the sloppy condition that I had been experiencing. I don't believe there is any wear on the screw, just the nut,
STEEL/BRASS Which is harder?
STEEL/BRASS Which is harder?
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Why, steel, of course. And the coefficient of both static and dynamic friction of steel on steel is lower than that of brass on steel. Which is one reason that no one used brass for gibs. However, a steel nut would be more expensive than a brass one, all other things being equal. Which I assume is the reason that feed screw nuts are usually made of brass.