Cross feed lead screw

sk1nner

sk1nner

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The cross feed on my Dar Sin 1237GH has had a lot of slop on it. After disassembling the carriage I've found that the screw and but are quite worn. I know that most of the import lathes were sold under a whole slew of names. I can not find any parts for the lathe under its designated name so I've been looking at similar machines under other names. The few parts listings I've been able to find show similar parts but not quite the same. I'm toying with the idea of buying an acme threaded rod and brass nut from McMaster and cutting the old worn threads off of the screw and attaching the new screw via a threaded stud. Does anyone have or know of a place I can obtain a good screw and nut, or have a better idea of how I could make this repair?
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you will probably have to modify the available nut to your machine specific geometry, or buy a tap and make your own nut.
 
I guess I would just buy a stock screw from McMaster and modify to fit. If the area between 4.5 and 6.75'' in the picture needs to be that diameter, then just shrink a sleeve onto the new screw. Looks like the rest is smaller than the root diameter of the threads.
 
Also, be aware that just because the nut afixing boss / hole looks like it Should be on center of the screw, it may not be. Need to check the alignment with the cross-slide sucked all the way in, then transfer drill the screw hole. Manufacturing errors?
 
The concept varies from one manufacturer to another, both domestic and imported machines. A lead screw "follower", be it on a lathe or some other machine, is sometimes cut as two pieces with a spring load between. They are a pain in the wazoo to reassemble after being taken down but are well worth the effort as the two sections under spring load will compensate for most backlash, as well as tolerate considerable wear.

I have a lathe from Taiwan (Grizzly G 1550) where the nut is cut almost through, leaving just a slim connection like a hinge. A grub screw is then passed into this gap to widen or release the two sections. This serves as well but must be manually adjusted on occasion as backlash becomes less tolerable. The spring works well until it doesn't, not giving much notice or lead time.

Making such a modification to a worn screw will give a little more use and possibly keeping a priority project on track and not from being sidelined.

.
 
Bi11Hudson said:
The concept varies from one manufacturer to another, both domestic and imported machines. A lead screw "follower", be it on a lathe or some other machine, is sometimes cut as two pieces with a spring load between. They are a pain in the wazoo to reassemble after being taken down but are well worth the effort as the two sections under spring load will compensate for most backlash, as well as tolerate considerable wear.

I have a lathe from Taiwan (Grizzly G 1550) where the nut is cut almost through, leaving just a slim connection like a hinge. A grub screw is then passed into this gap to widen or release the two sections. This serves as well but must be manually adjusted on occasion as backlash becomes less tolerable. The spring works well until it doesn't, not giving much notice or lead time.

Making such a modification to a worn screw will give a little more use and possibly keeping a priority project on track and not from being sidelined.

.
Click to expand...
So the possibility of making it a zero backlash nut could "fix" (mask) the worn portion instead of replacing the entire assembly. I hadn't though about that, probably easier and cheaper then replacing/remaking the whole thing. Thanks for the idea.
 
The split nut will work well if there is even wear of the lead screw. However, it most cases of wear with use, there is a central section where most of the use occurs that is worn whole at either end, there is almost no wear. You have two options with the split nut; adjust for acceptable backlash at the central section and live with a tight lead screw at either end or adjust for acceptable operation at the extremes and live with the increased backlash in the central section. A third option is to compromise and split the difference.

On the other hand, a double nut coupled with a spring will be self compensating for varying lead screw wear. I did this on my Atlas/Craftsman 6 x 18 with good results. Backlash was reduced to a few thousandths of the entire travel. On the Atlas lathe, I had an old nut which I used for the second nut. I milled a slot on the back side of the cross slide for an anti-rotation screw for the nut. I lost some of my far side travel as the nut would come off the lead screw but it wasn't enough to affect most operation and should I need the extended travel, I could remove the second nut and reassemble it when finished with the job.
 
RJSakowski said:
The split nut will work well if there is even wear of the lead screw. However, it most cases of wear with use, there is a central section where most of the use occurs that is worn whole at either end, there is almost no wear. You have two options with the split nut; adjust for acceptable backlash at the central section and live with a tight lead screw at either end or adjust for acceptable operation at the extremes and live with the increased backlash in the central section. A third option is to compromise and split the difference.

On the other hand, a double nut coupled with a spring will be self compensating for varying lead screw wear. I did this on my Atlas/Craftsman 6 x 18 with good results. Backlash was reduced to a few thousandths of the entire travel. On the Atlas lathe, I had an old nut which I used for the second nut. I milled a slot on the back side of the cross slide for an anti-rotation screw for the nut. I lost some of my far side travel as the nut would come off the lead screw but it wasn't enough to affect most operation and should I need the extended travel, I could remove the second nut and reassemble it when finished with the job.
Click to expand...
I've ordered 2 nuts the acme threaded rod and springs. My plan is to make a sketch of the screw and get the lathe operational. I will put the acme rod and extra but in storage. In the future I will make a new screw and replace the whole assembly. I appreciate your advice, and the time you took to clearly explain it to me.
 
My only addition is that you can buy the ACME threaded rod, and cut the original rod at the thread start and weld the reference surfaces (assuming they are still "reference surfaces".) I saw Keith Fenner do this on a restoration he was working on (to save machining time and associated hassle)
 
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