Craftsman 101.28940 Half Nut Skipping Teeth

T

tkalxx

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I have a craftsman 101.28940 that has recently started skipping teeth in the ~10" of travel closest to the chuck. I can only assume this is either due to leadscrew or half nut wear (or both). When I take a look at the half nut while it's engaged, it looks like the upper portion of the half nut is jumping around. Initially I thought it may be due to some run out on the leadscrew, but I measured the run out to be .005". I was able to get into the tight space and clean the half nut, along with the leadscrew but this made no difference.

Before I tear this thing apart, is there any adjustment for the half nut? It feels to me like the upper portion of the nut is loose. There is definitely some wear on the leadscrew, so I assume the half nut is pretty worn as well but I'd like to avoid replacing the screw if I can.

-Adam.
 
Just a suggestion, I don't know the answer.

Remove the saddle, determine if a spacer can be put behind the upper half (the looser one) to move it closer to the lead screw. If so, do so.

Also it may be possilbe to replace both halves of the half nut.
 
T Bredehoft said:
Just a suggestion, I don't know the answer.

Remove the saddle, determine if a spacer can be put behind the upper half (the looser one) to move it closer to the lead screw. If so, do so.

Also it may be possilbe to replace both halves of the half nut.
Click to expand...

That seems like a decent temporary solution. I would need to make a spacer that pushes the upper half down towards the screw. I haven't taken the half nuts a part yet, so I'm not exactly sure how they function or if this is even feasible. The exploded view in the manual that I have is a little confusing and doesn't show adequately how the half nuts function.

Janderso said:
https://www.ebay.com/itm/Atlas-Craftsman-9-12-9-10-12-Lathe-Half-Nuts-Split-Nut-/202639054831

I found these on the Bay.
Are they correct?
Click to expand...

Those are incorrect. My lathe has a 3/4" ACME screw. Half nut part# from the manual is 10F-12. It looks like this is the correct nut:

bmpartstech.com

Atlas / Craftsman 10F-12 10" & 12" Lathe Half Nuts / Split Nut - BM Parts Tech

To place an order please email: info@bmpartstech.com
bmpartstech.com
 
After a little digging, it looks like the half nuts engage using some pins and a scroll wheel when the lever is engaged. I don't think adding a spacer is an option.
 
I do not know about your particular lathe, but I do know that in general, there are several adjustments that can be made to the half nuts.

You first need to determine if they are worn out and need replacement. If not then you can start figuring out what adjustments to do.

My import lathe has half a dozen adjuster screws as part of the half-nut assembly
 
macardoso said:
I do not know about your particular lathe, but I do know that in general, there are several adjustments that can be made to the half nuts.

You first need to determine if they are worn out and need replacement. If not then you can start figuring out what adjustments to do.

My import lathe has half a dozen adjuster screws as part of the half-nut assembly
Click to expand...

I'll pull the half nut off the lathe later today to inspect it; it's a 35 year old lathe, I can only imagine it's worn and needs replacement. From the various images I've found online, there doesn't appear to be any obvious adjustments available. The manual doesn't state anything either.

You can see the pins (one on each half) that seat in the scroll wheel. When the scroll wheel is spun, the two halves come together.
Atlas-Craftsman-10-12-Lathe-Half-Nut-Assembly-_1.jpg images.jpg
Original-Atlas-Craftsman-10-12-Metal-Lathe-Half.jpg
 
Hmm, looking at that design, perhaps no adjustments are possible
 
On Atlas lathes there really aren't any adjustments. When it's worn you replace. I'm guessing both the leadscrew and the half nuts are worn
-Mark
 
Couple months ago I purchased rebuilt half nuts for my SB9.
They were probably original.
I’m back to cutting threads, etc.
I’d be inclined to buy new/rebuilt half nuts if it were me, they wear more than the leadscrew.
of Course, YMMV
Cheers
 
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