ball screw replacement

savarin

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Is there any reason why a ball screw should not be used in place of the cross slide lead screw?
I'm just thinking out loud here as I will be replacing my cross slide lead screw in my lathe some time soon to improve its huge backlash.
 
The friction on a ball screw is significantly less, so if used, the cross slide will tend to creep/move when under tension while turning. Most likely your cross slide nut is worn, so my recommendation would be to try to adjust it or replace it first. You should be able to get the backlash down to around 0.003".
 
Ball screw is likely to back drive under the cutting loads. Hey its a feature, every cut is a taper!
You would need to add a slide lock to the axis to prevent unwanted motion.

Or....... just replace the worn brass nut.
 
Ah, never considered the self feeding aspect, I was just thinking of the zero backlash and ease of movement.
Thanks
 
As others have said, ballscrews need holding force because they create such a small amount of friction when rotating. Personally, on a manual machine (assuming the leadscrew it has can't be repaired/reconditioned), the money would be better spent on a nice ground lead screw. I also noticed an increase in vibration when switching my X2 from the acme leadscrew to ballscrews. I attribute it to the decrease in contact area between the acme screw and nut and the ballscrew races and balls.
 
Ah, never considered the self feeding aspect, I was just thinking of the zero backlash and ease of movement.
Thanks
Commonly called back driving.
A general purpose ball screw and nut assembly will not have zero backlash itself, this requires one of several methods of preloading the screw such as 2 nuts that may be moved in relation to one another much like preloading bearings.

As seen here http://blog.misumiusa.com/ball-screw-preloads/
 
Thanks Wreck™Wreck
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I like the idea of the two nuts to reduce backlash its given me an idea for my cross slide.
Not that I'm anywhere close to doing it yet.
 
You are welcome.
For all intents and purposes lead screw backlash on a manual lathe is unimportant.
You are not interpolating radii on 2 sides are you?

For instance when turning the part pictured below the X axis must change direction, any backlash will become obvious. On a manual lathe the axis is moved in one direction only which makes any lash unimportant.

As a side note doing such a job requires cutting from both sides of the tool, in an ideal world the tool would have zero width therefore the tool point would describe the profile exactly, in the real world this is not possible however. A round profile tool works well yet requires using both sides of the tool. I used a .118" wide parting tool for this and offset the tool width on the back side with acceptable results, the mating internal ball socket was a whole nother story.

This is a test part to prove the program before running it.
 
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