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Ball screw reconditioning - regrind or oversize reload ... and servo recondition?

SRDC

Aluminum
Joined
Jul 2, 2014
Location
Texas, USA
Ball screw reconditioning advice - regrind or oversize reload? servo recondition?

Have a 1988 model CNC knee mill. Works great for our protoyping shop, as it is a support arm of our product development business. Makes the parts we need, and then we contract for production with someone with a production mill.

Anyway, the ballscrews have been progressively worsening over the past few months (brought it online early this year) - likely due to the several years of sitting before we got it, leading to dried out oil, etc. ... and us not realizing all the oiled parts needed to be flushed before running again (we just flushed, cleaned, and refilled the oil reservoir and actual pump, nothing farther).
The Y & Z ball screws are Tsubaki, external tube. The X ball screw is unmarked, but according to the place we have it at right now is high quality. It has internal tubes.

We have the ballscrews out for a quote to a reconditioning place a couple hours away - they are likely going to want to regrind / re-heat-treat the X-axis at least (apparently someone has monkeyed with it before, as they say it has 3 different sizes of balls ... 0.121, 0.124, and 0.125in). Another place is wanting to come out and reload them with oversize balls - says it takes advantage of the work hardening of the screws/nuts. What is your opinion? Is regrinding a problem? Preferred?

QUESTION 1: Is reloading with oversized balls going to sacrifice performance/longevity/something-else??? Is regrinding better or worse than oversize reloading?

Also, the place the ballscrews are at right now is claiming they need to examine the servo motors (SEM 26N-m / 5.5 running amp), as the x-axis is 'gray' (I can't see it - it looks like shiny metal with an oil film - some of it dried at the very ends - on it to me, but I'm no ballscrew expert). They claim that if I don't have them examine the servos and recondition them if necessary, that it could mess up my shiny 'new' ballscrews as it will make them work more (that's how I understand what they're saying the problem is).
Now, I can see that the servos can be overworked/overheated by bad ballscrews. But the budget for this piece of machinery isn't high at any given time ... and I don't understand how the servos being sub-optimal performance is going to destroy the ball screws, especially since the servos drive the ballscrews on all 3 axes by timing belts.

QUESTION 2: Does anybody here have any wisdom/input/opinions on servos destroying ball screws???

Thank you to everyone in advance!
 
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Have you compared prices with new Taiwanese screws ? I only mention that as a new Robodrill Mate, X axis screw is only $715, whereas the quote to fix the old one was 3 times that much.
 
I had looked at new screws - but they were through the manufacturer and were really pricey. Where did you get those, I'd appreciate a good source!
 
Well ... it looks like we're almost assuredly going to have to replace the ballscrews without benefit of measuring the original ones. Does anybody have any recommendations for places that would be able to help with replacement ballscrews if we can measure critical dimensions and provide pictures of the old ballscrews?
 








 
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