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SM 9" Ultilathe Crossslide nut and screw

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.

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Does that cross slide nut look right?
 

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YYCHM

(Craig)
Premium Member
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.

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Does that cross slide nut look right?

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

 
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YYCHM

(Craig)
Premium Member
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

I found your thread, mine looks the same as yours.


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.
 
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

(Craig)
Premium Member
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.
 

YotaBota

Mike
Premium Member
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.
 
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!
 
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.
 

Brent H

Ultra Member
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.
 

RobinHood

Ultra Member
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).
 
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).
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.
 

Darren

Ultra Member
Premium Member
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.
 

historicalarms

Ultra Member
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.
 
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.
 

YotaBota

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

eotrfish

Super User
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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