# Lead Screw Problem - Craftsman 6”



## Voda2000 (Oct 26, 2020)

Hi, I’ve finally got back to working on my Craftsman 101.20140 lathe I got last year. So far I have had to replace the cross feed nut and the pinion gear on the rack. I also added a QCTP to replace the broken lantern and I’m quite happy with how it’s working. 

I had noticed it was cutting a taper so I attempted to level the lathe last night.  I don’t have a machinist level so I did a few test cuts on a 12” bar and was working back and forth to see if I could get the cuts the same.  After realizing the tail stock was way out of alignment I was able to get it to about 0.002” which I was happy with given my method. 

When I went to take a pass along the whole bar with the power feed the half nuts started “skipping” in the middle. I’m not sure if that’s the right term but it’s like the are crawling up and over the threads on the lead screw. 

When I got the lathe, the half nuts wouldn’t hold the screw at all. I shimmed them a little between the back of the carriage and the nuts and this seemed to help but I was assuming it was a temporary fix. The lead screw threads don’t look pointy but they are not square either.  I have cleaned the nuts and the lead screw and picked out all the debris. Given the number of odd things when I got the lathe I wouldn’t be surprised if the previous owner had used the half wheel with the half nuts engaged. 

My question is about what my next steps would be.  I had got a quote a year ago from Clausing and the lead screw is about $150 and the half nuts are $50.  I’m in Canada so the shipping will be steep and I prefer to try  and minimize the number of orders. I am planning on keeping the lathe long term as it is the appropriate for the small work I do so I don’t mind putting some money into it. 

Is it likely just the half nuts are worn?

Should I just bite the bullet and replace both?  

With a worn lead screw ware out new half nuts quickly?


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## markba633csi (Oct 26, 2020)

When I got mine, the leadscrew was badly worn. I found a very nice used one on Ebay.  I also replaced (I think) one of the half nuts, and cleaned everything completely, using a string to clean the screw while running slowly. 
The nuts really need to be in good shape for this to work well.  Also the leadscrew should be decent and not bent.  Check the carriage also for binding- it should move freely. On a lathe with a worn bed, you may have to make a compromise with the shims; you may not have full easy travel all the way down to the tailstock, depending on the degree of wear.  
-Mark


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## Voda2000 (Oct 26, 2020)

Thanks Mark. I checked Ebay but all the used ones are coming from the US and the shipping plus the item is as much as ordering it new. Ebay kills Canadians with shipping sometimes. 

Carriage is moving freely but I’ll double check. Maybe after leveling the lathe it is binding a little. 

I’m going pull the half nuts tonight and take another look at them but I think they are pretty worn. 

Would the easiest way to check the lead screw for a bend to be to just run it with a straight edge?  How straight does it need to be?

I’m really torn between just trying new half nuts and try to save $150 or just replace it all...

How much wear on the lead screw is too much?


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## phubbman (Oct 26, 2020)

The half nuts are intentionally softer than the lead screw so that they wear out before the lead screw does.  They're meant to wear out.  Not that the lead screw couldn't be worn, but it's probably the half nuts.  

If the threads are worn, they will look rounded off instead of having crisp edges at the peaks and valleys of the threads.  If you need to buy new ones, consider getting two pair.  That may take some of the sting out of the shipping costs, and you'd have another set on hand for when the new ones wear out.


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## pontiac428 (Oct 26, 2020)

Lead screws are easy to make for the Atlas.  Acme threaded rod is pretty cheap.  I replaced all of my lead screws with stock from McMaster.  Just copy what you have on your machine while it still runs, then do the replacement.  The Acme rod will cost less than the nuts do.  It will make a positive difference if you replace all of the screws, nuts, and half nuts while you're doing it, and will last for your lifetime under hobby use.


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## Voda2000 (Oct 26, 2020)

Thank guys. 

I just took another look at it and it seems most of the wear on the lead screw is in the middle.  It sure the history of this lathe so I don’t know why there particularly.  Not sure how bad this would be considered. 






The half nuts look done to me.  Here’s a few photos. Any thoughts? 
	

		
			
		

		
	






I had a look at McMasters site but I could find Acme precision ground 1/2-16tpi. Anyone have a link? Seems like it would be simple enough to machine it myself from a threaded rod.


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## pontiac428 (Oct 26, 2020)

Are you sure it's 16 tpi?  10 is a more reasonable pitch for a lead screw, especially since your handwheels are marked .100 per turn...

You could machine it.  Lots have, even on this site.  It's just a matter of making an Acme thread cutting profile tool. I prefer to buy commercial for lead screws, since it is a "standard" to which the movement of your lathe is calibrated. It may be a throwback to my lab days, but a commercial operation can grind a more precise and uniform lead screw than my lathe can by the time I factor in gear play and all the wear points along the way on my old lathe. Four feet of 1/2-10 is $10 from McMaster.  At that price, it isn't even worth my time to try!


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## Voda2000 (Oct 26, 2020)

I read it was 1/2”-16tpi in another site but perhaps that is wrong?  Maybe some can confirm that one way or the other.  Turning down the ends for the bearings would be easy enough if I had a pre threaded rod. 

I could try to make my own from a scratch but I’m fairly new to machining and have yet to do any single point threading. Also I would need a functioning lathe to cut the threads on.


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## francist (Oct 26, 2020)




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## wa5cab (Oct 27, 2020)

Assuming that the model number of your lathe is 101.21400 and not 101.20140 as you wrote, then the only differences between it and the Atlas 618 are the printing on the badges and nameplate.  The lead screw diameter and pitch are 1/2"-16 acme  as you said.  The pitch of the lead screw has nothing to do with the markings on the cross feed.  That screw is (where there is a relation) is 3/8"-10 Acme.

Both your lead screw and half nuts are worn out,  Even were the lathe bed long enough to make a new lead screw (which it isn't as the lead screw is longer than the maximum center to center rating of the lathe), you would not be happy with the accuracy of the results.  It is long enough, however, to machine the ends of a 2 or three foot long piece of precision Acme threaded rod given that the lead screw will just fit through the hollow spindle. To do it, you will need to have a steady rest or rig up an outboard bearing to support the left end if the rod.  However, I would not recommend trying to do it despite what a few others have done.  You might try to find someone close enough to the factory to pick it up and who has a Stamps.com  account.  The reason for the Stamps.com account is that they recently added for shipping to Canada a way to prepay the customs and tax  so that you don't have to go through all of that.  However, I don't know what the cost would be as the only time I have used it was on a radio part that cost less than $10.00 US.  The fee was $6.95.  But I don't know whether that was a flat rate or based on the declared value of the part.


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## pontiac428 (Oct 27, 2020)

Yeah, I was thinking lead screws as in screws that drive movement (compound and cross) compared to feed screws for threading.  The Atlas has one screw for both purposes on the carriage, except the carriage is moved by the handwheel and fed by the feed screw... but it's also a lead screw because the names are somewhat interchangeable depending on who you ask and how many drinks they've had.  So disregard anything I said about lead screws, none of that will apply to your feed screw.  If you buy the correct threaded rod for your needs, you can still work the ends of the rod as needed on your lathe because the spindle is hollow.  Custom precision Acme rod is available for an attainable price in the US.  I feel your pain on shipping, I lived overseas for 10 years and had hobbies then, too.


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## markba633csi (Oct 28, 2020)

Yes your leadscrew is worn out- that's what mine looked like.  Not sure about the half nuts but they are probably worn too.
My feeling is that the screw on these lathes should be used mostly for threading; using it frequently for feeding wears it and the nuts much too quickly.
-Mark


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## Voda2000 (Oct 28, 2020)

Thanks everyone. 

Yes that was a typo on the middle number. It’s 101.21400. 

I’m glad the consensus is that is worn out. Not that I want to spend the money but I didn’t want to replace parts that were still serviceable. 

I got everything taken apart tonight and the rest seem good. I wasn’t able to remove the pin that holds the collar on but from the looks of the replacement part that collar is already installed. 

I don’t think there is anything else I need to order form them but the half nuts and the screw. But I will double check before ordering from Clausing. 

Has anyone ordered the screw from Clasuing?  Just wondered if there is anything I needed to know about it.   

I agree and can see the problem using it for feeding as opposed to threading.  My thought had been it’s really only good for a final very light finish in pass if used for feeding. 

I do remember seeing something someone rigged up with a second screw below it that ran off a drill for feeding so as to not wear out the screw.


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## WCraig (Oct 29, 2020)

Voda2000 said:


> I wasn’t able to remove the pin that holds the collar on but from the looks of the replacement part that collar is already installed.



Is this the collar that would not come off?  If so, I had the same problem.  I destroyed two pin punches and burned a bottle of gas trying to get it free.



My lead screw should probably be replaced, as well.  I believe I'm going to have to try to drill out pin or cut the collar off with a Dremel if/when I get there.  

Craig


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## wa5cab (Oct 29, 2020)

According to the later 6" parts lists, the lead screw and left-end collar are not available separately.  Unlike the 9", 10" and both of the 12" model groups, the 6" lead screw should only be removed to the left.  In other words, you do not need to remove the left hand collar  in order to remove the lead screw.  And spending any time removing the left hand collar would be time and effort wasted.  Note, however, that this only applies to the various 6" models.  

The half nuts wear more quickly than the lead screw.  Especially if you or a PO installed brass ones.  Therefore, unless you happen to know that the half nuts have been recently replaced, if the lead screw needs to be replaced, so do the half nuts.  

Also, if any of you do the replacements, and follow the standard lubrication instructions, it is highly unlikely that you will live long enough to ever need to do it again.  And that is assuming that you don't fall victim to hysteria and cease using the lead screw for routine turning.


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## Voda2000 (Oct 29, 2020)

Hi Craig, ya that’s the one that I couldn’t get off, mine is completely flush. As was pointed out there really isn’t any reason to. The only thing I discovered was I didn’t have enough clearance to the left of my lathe to slide it out so I just unscrewed the bearing from the bed and then took it apart on my bench.

Hi Wa5cab, thanks for the confirmation. I have no idea how old they are (wouldn’t surprise me if original) but I’ll order both the new half nuts and lead screw.  Thanks!


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## Voda2000 (Nov 13, 2020)

Got the new lead screw and half nuts last night. I’ll start the assembly this weekend. Any tips or anything I need to know about putting this back together?


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## Voda2000 (Nov 14, 2020)

Well just to close this up, I finished the install.  The replacement parts made it quite clear how much wear was on the old parts. 

A couple of words of caution. The new collar on the lead screw is slightly thicker than the original. It doesn’t seem like a big issue initially but when you looks at how close the gears run to it, it can interfere. I chucked it in the lathe and faced it. I don’t remember how much I took off exactly but it was in 0.020-0.030” range.  I also had to shorten the the shaft by that same amount to make sure the bolt in the end would snug up again the gear.  

I also noticed the bolt in the end of the lead screw had been replaced at some point with one that was too long and they used a stack of washers to make it work. I just shorted the bolt and it worked fine. 

Once it wall all reassembled it runs great.  Thanks everyone for the help.


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## wa5cab (Nov 15, 2020)

If the bolt in the end of the shaft (when shortened to the proper length) could draw the gear and keyed spacer up tight against the collar before you took a little off of the collar left face, then you should have thinned the collar from the right face instead of the left.

I would suggest that you call Clausing and report the collar thickness error.


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## Voda2000 (Nov 15, 2020)

I don’t think I explained it correctly. This thread is someone who had a similar problem: https://www.hobby-machinist.com/thr...-atlas-craftsman-6-lathe-from-clausing.32498/

The problem comes down to the clearance between the gear in the photo I’m pointing to and the collar 




You are right that if I took some off the right side I may not have had to shorten the end for the bolt but I’m not 100% on that as I didn’t measure it to start with.  I seemed easier to take some off the left side when it was in the lathe but I’m new this and I’m sure it could be done the other way.  And honestly I didn’t consider that the end would need to be shortened too when it took some off the left side. Live and learn. 

Regarding Clausing, I’m just happy I could get a part and if I have to do a little fitting to get my clearance right so be it. It’s also a succeeded part number so that may have something to do with the discrepancy in the thickness. 

I appreciate the feed back. I did get some practice “fixing it” so I’m a making small steps in my machining knowledge.


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## Voda2000 (Nov 15, 2020)

I also just wanted to add that this wasn’t meant to be a complaint about Clausing. Just a heads up for anyone else that is getting a replacement to check the collar before reassembling it and finding gear dragging on the collar.


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## wa5cab (Nov 16, 2020)

OK.  My comment was more for anyone else who encounters the same issue in the future.  It is also possible that on the assembly line when yours was originally being built, that all of the various dimensions were on the high side of the tolerances (the "Perfect Storm"  syndrome) and the machine required some file to fit in order to get it finished.  Anyway, I would recommend that anyone else who needs to replace the lead screw to expect it to come with the collar already installed (so don't waste any time attempting to remove the old one).  And to measure the thickness of the collar and the distance of its left face from the left end of the lead screw  And then proceed accordingly.


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## Voda2000 (Nov 18, 2020)

Very good point. I kind of wondered about the possible of the tolerances adding up. I’ve seen that before on a automotive parts. 

Next thing for this lathe is to track down a 3 jaw chuck.


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