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

----- Original Message -----
From: "Leslie M. Watts" <leswatts@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Saturday, September 27, 2003 8:13 AM
Subject: RE: [CAD_CAM_EDM_DRO] Preloading ball screws


> Hi Bill
>
> Interesting problem...and I don't think the issue is covered
> as much as it should be.
>
> I agree completely with Carlos in that the inability of the threaded
> portion to backdrive would cause it to tighten to the highest
> pitch portion of the screw and stay there, causing massive loads
> on the bearings when they later went over a lower pitch area.
>
> So you really need a stiff compact axial spring force between the nuts
> that doesn't exceed about 5% of max dynamic load in areas of
> maximum d(pitch)/dlength.
>
> What about stacked Belville washers? I use them for rotary bearing
> preloading commonly. Big spring constant, compact geometry.
> I realize it would be some surgery to do that, but if the threaded
> block were split and fastened with Belvilles on both faces of one
> section (for bidirectional loading) it would take almost no extra
> room.
>
> Just something to think about.
>
> Les
>
> 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:
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> http://www.lmwatts.com/signwp.html
>
>
>
>
> -----Original Message-----
> From: Carlos Guillermo [mailto:carlos@...]
> Sent: Saturday, September 27, 2003 2:33 AM
> To: CAD_CAM_EDM_DRO@yahoogroups.com
> Subject: RE: [CAD_CAM_EDM_DRO] Preloading ball screws
>
>
> Hi Bill -
>
> I see a problem with that arrangement. The spring-loaded ballnut
> would not be backdriveable in its mounting threads, so although it
> would tighten up the nuts against each other on the areas of the
> screw with lower pitch, it would not allow the nuts to open up on
> areas of the screw with higher pitch. You would not have constant
> preload, just a system that eliminated backlash, but then caused
> potentially excessive ball contact forces when the screw pitch
> increased.
>
> Regards,
>
> Carlos Guillermo
> VERVE Engineering & Design
>
> -----Original Message-----
> From: Bill Kichman [mailto:billkichman@...]
> Sent: Friday, September 26, 2003 7:21 PM
> To: CAD_CAM_EDM_DRO@yahoogroups.com
> Subject: [CAD_CAM_EDM_DRO] Preloading ball screws
>
> I am sure this has been covered ad nauseum, but here goes...I have
> 2
> ballnuts threaded into a steel block which is attached to my table
> for my
> ballscrew conversion...I had been depending on rigid backlash
> adjustment by
> simply screwing one of the nuts tightly against the other, and
> tightening
> both setscrews. As I understand it, a spring type arrangement is
> more
> advantageous due to wear issues which act to change the fixed
> preload over
> time.
>
> My question is this....as I have no room whatsoever on at least
> one of the
> axes for adding anything to the periphery of the nut, and the
> threads
> already are there, would it be reasonable to attach a strong
> spring such
> that it would act to tighten the threaded ball nut's threads at
> all times?
> That way, the spring wouldn't have to be nearly as strong as an
> installation
> without the threads installed and a heavy spring arrrangement
> in-line with
> the nut. Am I seeing this clearly? The spring could partially
> wrap around
> the nut and keep a constant preload.
> Has anybody done this?
> R. William Kichman, P.E.
> Kichman Engineering Associates
> 103 Old Furnace Road
> Cornwall, PA 17016-0643
> tel/fax 717/270-0714
>
>
>
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