# SM 9" Ultilathe Crossslide nut and screw



## calgaryguy (Mar 12, 2022)

Disassembled the Ultilathe a bit today for cleaning and inspection. Removed the carriage, crossslide and compound.

THe cross slide ACME screw looks to be in quite good shape, and the bronze nut does as well, HOWEVER, this cross slide nut looks alot different than one that was in either @YYCHM or @YotaBota 's threads on their SM 9" reconditioning.



























Does that cross slide nut look right?


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## YYCHM (Mar 12, 2022)

calgaryguy said:


> Disassembled the Ultilathe a bit today for cleaning and inspection. Removed the carriage, crossslide and compound.
> 
> THe cross slide ACME screw looks to be in quite good shape, and the bronze nut does as well, HOWEVER, this cross slide nut looks alot different than one that was in either @YYCHM or @YotaBota 's threads on their SM 9" reconditioning.
> 
> ...



Looks ok to me.  Does it hang up some where?  Why are you questioning it?  That screw looks to be in great shape.


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## calgaryguy (Mar 12, 2022)

YYCHM said:


> Looks ok to me.  Does it hang up some where?  Why are you questioning it?  That screw looks to be in great shape.


Not questioning it 'much' really. I just seem to recall a bronze nut someone machined for a SM lathe that someone made from scratch.

The cross slide had about .010-.012 of 'backlash' measured on the cross slide dial before disassembly. How much backlash should I be seeing?



I found your thread, my cross slide nut looks the same as yours.

*








						9" SM Utilathe Restoration
					

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*


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## YYCHM (Mar 12, 2022)

calgaryguy said:


> Not questioning it 'much' really. I just seem to recall a bronze nut someone machined for a SM lathe that someone made from scratch.
> 
> The cross slide had about .010-.012 of 'backlash' measured on the cross slide dial before disassembly
> 
> ...



0.012 sounds about right. I've made 1 or 2 nuts from brass.  I have a 1/2-10 LH Acme tap if you want to try making a new nut.


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## calgaryguy (Mar 12, 2022)

YYCHM said:


> 0.012 sounds about right. I've made 1 or 2 nuts from brass.  I have a 1/2-10 LH Acme tap if you want to try making a new nut.


Oh maybe its brass and not bronze. My 'gold colored' metal lump identification skills are pretty rookie.

If .010-.012 is expected then cool. I should add that the nut is slightly 'looser' in fit at the very start (like first 5 threads or so) of the acme threads on the shaft. Area cicled in black below. I assume this is because the majority of the wear in the shaft is on these first few acme threads.


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## YYCHM (Mar 12, 2022)

Brass Bronze what ever.  The original was probably bronze.  The majority of the wear is typically in the middle of the screw.  I wouldn't worry about the first 5 threads you won't use them.  Your screw looks really good.


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## calgaryguy (Mar 12, 2022)

YYCHM said:


> Your screw looks really good.


Thats what Im finding so far - minimal-moderate wear for what seems to be a 30? or 40? year old machine.


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## YotaBota (Mar 12, 2022)

calgaryguy said:


> Thats what Im finding so far - minimal-moderate wear for what seems to be a 30? or 40? year old machine.


It's probably more like from the 50's or 60's. At some point SM changed the colour on the thread chart to blue but I haven't narrowed down when that was done.
The nut looks like it could have been replaced, my old one had a rounded bottom on it. If it works smooth it sounds reasonably tight then I wouldn't worry about it unless you want the practice.


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## calgaryguy (Mar 12, 2022)

YotaBota said:


> If it works smooth it sounds reasonably tight then I wouldn't worry about it unless you want the practice.



NO practice for now. This is the cleaning and inspection phase to identify anything badly out of spec. I.e.; if someone say 'crossfeed handle backlash should be .003 as read on the crossfeed dial' then I'd be digging into replacing things. Cheers!


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## YYCHM (Mar 12, 2022)

calgaryguy said:


> NO practice for now. This is the cleaning and inspection phase to identify anything badly out of spec. I.e.; if someone say 'crossfeed handle backlash should be .003 as read on the crossfeed dial' then I'd be digging into replacing things. Cheers!



0.003  I wish


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## calgaryguy (Mar 12, 2022)

I really dont have a point of reference for how tight or loose any of this stuff should be. Hence I'll be driving you guys nuts with questions.


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## Brent H (Mar 12, 2022)

I have made a few for the 10” Utilathe, also a new screw.  

Basically you want to remove backlash on the cuts - really basic video: 




I like working at less than 0.005” backlash on the dials. - somewhere in Craig’s dream land - LOL.


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## RobinHood (Mar 12, 2022)

If you use a tap to make a new nut, it might be difficult to reduce the backlash much below 10 thou. The best bet would be to single point the internal thread. It will give you the ability to get it just right for the existing lead screw.

The other way is to make a split nut (using the tap). Either use a spring or a wedge system to reduce backlash to the value you want.

BTW, Bridgeport uses a split nut on the axis. For longevity and best results, they recommend that backlash be adjust to 7 thou.

If you are looking for near zero backlash, the best system is high precision, ground ball screws ($$$$s).


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## calgaryguy (Mar 13, 2022)

RobinHood said:


> If you use a tap to make a new nut, it might be difficult to reduce the backlash much below 10 thou. The best bet would be to single point the internal thread. It will give you the ability to get it just right for the existing lead screw.
> 
> The other way is to make a split nut (using the tap). Either use a spring or a wedge system to reduce backlash to the value you want.
> 
> ...


Zero backlash isnt what I'm after I dont think. I'm after an 'acceptable' level of backlash for a manual lathe. .010-.012 seems 'normal' for the age of the machine. and I can live with it for now.

If/when I go down the route of reducing backlash in this cross slide screw/nut I'll likely tackle making a new nut and a new shaft at the same time.

Just to give everyone some context here:

I had read thru @YotaBota and @YYCHM 's threads on their Utilathe restorations and both indicated they had issues with the cross slide nut/shaft which needed addressing. This made me curious as to what shape my crossslide nut/screw was in so I disassembled it and came looking for advice and context on whats 'acceptable' backlash for now.


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## Darren (Mar 13, 2022)

Backlash on a lathe is a lot less of an issue than backlash on a mill. Even a new lathe will have a few thou as read on the dial, so if you have 10-12 its not really an issue in use. You will notice it more when doing operations like threading, as you have to go past the backlash and back in to your number. You can look into splitting the nut to add some adjustment.


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## historicalarms (Mar 13, 2022)

I have seen cross slide nuts with a built-in runout adjustment. They have slice through the rod threads with an adjustment screw from one end of the nut, through the slice & into the other end of the nut. The idea is that when the screw is tightened it draws the acme threads together ever so slightly that threads from both ends of the nut grip the rod threads with tighter tolerance, reducing run out.

    To add; the slice isnt all the way through the nut ,just deep enough that the screw can pull/flex the other end into each other.


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## YotaBota (Mar 13, 2022)

calgaryguy said:


> Does that cross slide nut look right?


Yup, looks the same size and shape as my old one.


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## calgaryguy (Mar 13, 2022)

Cool. I've taken some measurements of the shaft and nut. Once I have this back together I will likely take a shot at making a new shaft and nut with single point threading.


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## YotaBota (Mar 13, 2022)

When I made my new screw I ordered a 3' length of 1144 rod, it work out very well.








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The nut was from a hunk of brass I had kicking around and tapped the hole. Single pointing that small a hole should be fun to watch, you'll have to report how it goes.


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## eotrfish (Mar 14, 2022)

historicalarms said:


> I have seen cross slide nuts with a built-in runout adjustment. They have slice through the rod threads with an adjustment screw from one end of the nut, through the slice & into the other end of the nut. The idea is that when the screw is tightened it draws the acme threads together ever so slightly that threads from both ends of the nut grip the rod threads with tighter tolerance, reducing run out.
> 
> To add; the slice isnt all the way through the nut ,just deep enough that the screw can pull/flex the other end into each other.


 Here's a pic of the cross slide assembly on my Maximat Super 11.   The nut is held in place with a SHC and the pointed set screw engages the slit in the nut.  I have mine adjusted to .002" backlash.  I think I've had to adjust it 3 or 4 times in the 40 years that I've had the lathe.


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## YYCHM (Apr 3, 2022)

This thread peaked my curiosity, so I ventured on another backlash reduction x-slide nut creation..... 






With this nut I can tweak backlash down to 1/2 thou from 1-1/2 thou (original nut), however it's tight at the extreme ends of the lead screw which is to be expected of a worn screw I guess.  Is backlash really worth chasing if you know about it and compensate?


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## Darren (Apr 4, 2022)

YYCHM said:


> This thread peaked my curiosity, so I ventured on another backlash reduction x-slide nut creation.....
> 
> View attachment 22772
> 
> With this nut I can tweak backlash down to 1/2 thou from 1-1/2 thou (original nut), however it's tight at the extreme ends of the lead screw which is to be expected of a worn screw I guess.  Is backlash really worth chasing if you know about it and compensate?


Its worth chasing on a mill, but backlash on a lathe really isn't important as long as you are aware of it.


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## PeterT (Apr 4, 2022)

Some people feel that excess backlash can adversely affect parting (chatter, poorer cutting performance). As to why this would be I cant really say. One would think once the lash is taken out as you in-feed, screw threads are fully contacting against nut thread, it should be the same right? But maybe the devil is in the details as you are hand feeding at non-perfect handwheel rpm, that micro-momentary pause + some slop could maybe initiate chatter & then it worsens on on its own. I dunno. Parting is one of hose things where pick one of 7 possible issues can cause problems. But I've heard people say when they replaced their worn feedscrew or tightened the ABL nut the problems went away or diminished. Now did they also reset their gibs while doing this job & that contributed to cutting improvement? Hard to know. 

Now that my ABL nut is tighter I feel like the infeed control is crisper & maybe overall finish has improved all things equal. Maybe its just allowing the table lock to hold better. But it comes at the expense of feedscrew & nut wear. I have a spare so not too worried. I'll post some pics of my feedcsrew assembly but its nothing special. What you made on your own is an improvement over what is standard on my lathe.


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## PeterT (Apr 4, 2022)

YYCHM said:


> With this nut I can tweak backlash down to 1/2 thou from 1-1/2 thou (original nut), however it's tight at the extreme ends of the lead screw which is to be expected of a worn screw I guess.  Is backlash really worth chasing if you know about it and compensate?



I just read this again. Do you mean just pushing & pulling on the table you only displace 0.0005" to 0.0015" (or dead band in the dial = same thing). That's nothing. Maybe even considered too tight & premature wear? I always assumed 0.010" was a normal starting point & wear compromise. What do others set theirs at?


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## YYCHM (Apr 4, 2022)

PeterT said:


> I just read this again. Do you mean just pushing & pulling on the table you only displace 0.0005" to 0.0015" (or dead band in the dial = same thing). That's nothing. Maybe even considered too tight & premature wear? I always assumed 0.010" was a normal starting point & wear compromise. What do others set theirs at?



I messed up using the thou term again.  Initial dead band dial backlash was 0.015", final backlash is 0.005".  So 5 thou v.s. 15 thou?


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## Brent H (Apr 4, 2022)

5 is great Craig - bravo!


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