RE: [CAD_CAM_EDM_DRO] Preloading ball screws

Bill,

The easiest way to adjust Belvilles is by controlled
angular displacement of the stud, bolt, or nut.
The spring rates are given... I have the
MSC catalog open here and I see many that would be in range.

Perhaps studs, bolts and Belvilles could be recessed in counterbored
holes or something? Hard to know without pictures and diagrams.

If you have typical 1" or so rolled screws with a normal several thousandths
of backlash total preload for 5% max dynamic might
be in the couple hundred pound area.

I considered a variant of your torsional preload idea where
it is applied to a floating nut (not screwed into a block).
That would backdrive, but I think it could end up with
some complications as well.

I also saw Ron's post about larger balls. I use factory oversize
ball preload nuts on my stuff. I have watched HIWIN do that at
the midwest US warehouse. Lots of little trays with balls marked
+5 or -5 microns and such. And Tweezers. I'm not trying it! :^)

My understanding from them is that you need a very consistently rolled
gothic arch (4 point contact) raceway to have this work.

I know larger balls are used to REDUCE backlash often without
being a preloaded forced fit as my units are. That probably works with
any raceway geometry.

Leslie M.Watts
L M Watts Furniture
Tiger Georgia USA
(706) 212-0242
http://www.lmwatts.com
Engineering page:
http://www.lmwatts.com/shop.html
CNC surplus for sale:
http://www.lmwatts.com/forsale.html
CNC carved signs:
http://www.lmwatts.com/signwp.html




-----Original Message-----
From: Bill Kichman [mailto:billkichman@...]
Sent: Saturday, September 27, 2003 10:22 AM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: Re: [CAD_CAM_EDM_DRO] Preloading ball screws


Leslie, that's an inteesting solution, and I agree with you guys' correction
related to back-driving and excessive torque. Now how does one tighten the
belleville washers once they are in place, I like the idea, but the mill's
steel on 2 adjacent sides of the nut assembly resides about 1/8" away,
essentially eliminating the possibility for adding threaded studs or the
like alongside to tension everything.


R. William Kichman, P.E.
Kichman Engineering Associates
103 Old Furnace Road
Cornwall, PA 17016-0643
tel/fax 717/270-0714