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Thread: Ballscrew Nut Re-fit
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23rd Oct 2019, 05:26 PM #31Golden Member
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- Apr 2009
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- Kingswood
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Roger,
Thanks for the comments.
Loved the bucket photo, I use a re-cycled food tray on the bench.
The reason I chickened out on the size increase was just the risks you mentioned.
I was chasing the "stickyness" of the nut on the screw, a few rotations before coasting to a stop after starting by hand.
It seems to me, about 18 microns backlash in the ballscrew is OK for a turret mill X-axis.
I am sure there will be more in the toothed rubber belts.
Can you provide any references for the effect of ball size increase or acceptable backlash in the nut ?
I have found it very hard to get this sort of information.
John
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23rd Oct 2019, 06:59 PM #32Senior Member
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- Jun 2016
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servicing
It seems to me, about 18 microns backlash in the ballscrew is OK for a turret mill X-axis.
Depends on what you want from the machine. My system resolution is 0.8 um, and I routinely zero it to 10 um. I can go tighter if warranted (5 um is easy enough), but that is only for some jobs.
I am sure there will be more in the toothed rubber belts.
With the older timing belts such are used on cars, yes, but if you change to the GT2 or GT3 profile there will be essentially zero backlash. And those GT2 belts are VERY strong. You just need to have the right tension on them to seat the tooth profile. That is, the European ones, not the Chinese ones. The latter may still be fairly good.
The whole subject of 5 um size changes in ball nuts is a bit obsolete today. You can try to get minimal backlash with a single nut, but it is not worth while. For CNC work we use double ball nuts spring-loaded apart, to reduce the backlash to very close to <1 um. That changes everything.
Cheers
Roger
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