Lathe ball screw backlash

bpratl

bpratl

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I just installed a ball screw (Thomson .750 x .200) to my G0602 to enhance the ELS conversion and eliminate the troublesome half-nuts misalignment and friction. So far it works great; but I am concerned about the .007" backlash, which to me seems excessive. What should be the maximum backlash one could expect, from a new ball screw and ball nut? Both items were purchased for McMasters-Carr. Bob
 
That does seem a bit much. First I'd check with Mcmaster on the specs for this part. They are EXTREMELY helpful.

real good chance your problem is in the thrust bearing setup, not the ball assembly. Find a place to put an indicator to find out how much the screw is shifting in the thrust bearings.

Karl
 
from what I have read most have two ball nute that tighten against each other with shims to preload them. Have you done this or what ever means your set up has for removing the BL
 
You probably won't get to zero without double nuts. You could get closer by changing the balls out. There are a couple guys selling the balls on ebay. Google Hoss G0704, he did some of that and had links posted in his cnc thread.

Dave
 
Karl_T said:
That does seem a bit much. First I'd check with Mcmaster on the specs for this part. They are EXTREMELY helpful.
real good chance your problem is in the thrust bearing setup, not the ball assembly. Find a place to put an indicator to find out how much the screw is shifting in the thrust bearings.
Karl
Click to expand...

I will give McMaster's a call as you suggested. There is no backlash on the ball screw as it has adjustable thrust bearings, on both sides, that I can adjust for zero backlash.
The backlash was determined by a dial indicator and the digital readout on the ELS controller which read the same for 30" of the lead screw.
 
I will offer what I was just told as well the other day regarding my Thomson ball screws from my Mill's builder. That my unit has Thomson screws which were liked but often did have some higher BL values Mine is listed as .125 balls nominal which my Mill guy notes were almost always undersized to .122-123 He suggested I buy some better .125's and replace the ones I have. I just ordered 100 for $9 from Grainger. Good to .0001 I have 67 to do. Just something to try while I have my Saddle apart for other clean/reburb reasons. Being new I asked if there was anything I could do w/ the ball screws while I had everything apart.... Glad I asked him. Love to tinker w/ this thing anyway. I'll post what I find when I take out my 67 BB's. No clue if this is related to your issue but since you said my MFR I thought I should offer what I was just told too ;-)
 
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countryguy said:
I will offer that I was just told as well the other day regarding my Thomson ball screws from my Mill's builder. That my unit has Thomson screws which were liked but often did have some higher BL values Mine is listed as .125 balls nominal which my Mill guy notes were almost always undersized to .122-123 He suggested I buy some better .125's and replace the ones I have. I just ordered 100 for $9 from Grainger. Good to .0001 I have 67 to do. Just something to try while I have my Saddle apart for other clean/reburb reasons. Being new I asked if there was anything I could do w/ the ball screws while I had everything apart.... Glad I asked him. Love to tinker w/ this thing anyway. I'll post what I find when I take out my 67 BB's. No clue if this is related to your issue but since you said my MFR I thought I should offer what I was just told too ;-)
Click to expand...

I just measured the balls, from my ball nut, and as you stated they are .12380" so I order the .125" ball from Grainger and will give it a try. Let me know how you make out and I will post my results when I try them. Thanks for the info. Bob
 
I think changing out the ball screw balls will tighten it right up once you preload it properly. Just make sure that you replace them with the exact number that you removed. that should lower back lash a bunch.

Bob
 
Yeah- I hope so as well. I ordered 200. Enough for my z axis as well which is not right either. I should have 67 of them to roll around!
 
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