# Cross feed lead screw



## sk1nner (Nov 27, 2022)

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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## OTmachine (Nov 27, 2022)

Green Bay Manufacturing
					

Chemistry - Responsive Muti-Purpose Portfolio Template




					greenbaymfgco.com
				



you will probably have to modify the available nut to your machine specific geometry, or buy a tap and make your own nut.


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## sk1nner (Nov 27, 2022)

OTmachine said:


> Green Bay Manufacturing
> 
> 
> Chemistry - Responsive Muti-Purpose Portfolio Template
> ...


My plan if I go this direction is to mod the McMaster nut to work.


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## JimDawson (Nov 27, 2022)

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.


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## OTmachine (Nov 27, 2022)

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?


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## Bi11Hudson (Nov 27, 2022)

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.

.


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## sk1nner (Nov 27, 2022)

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.
> 
> ...


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.


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## RJSakowski (Nov 27, 2022)

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.


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## sk1nner (Nov 27, 2022)

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.


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.


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## Mitch Alsup (Dec 2, 2022)

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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## aliva (Dec 3, 2022)

What I did was to make new nut from bronze. Instead of buying an expensive $100. tap I took the best part of the old lead screw and made a tap. Just had to harden it, worked fine


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## sk1nner (Dec 4, 2022)

I scabbed the screw together yesterday.  I'll get it installed today and see how it works.


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