Re: [CAD_CAM_EDM_DRO] Ballscrew loads. Was Bent Nook ballscrews ?????

On Tue, 2003-08-12 at 23:32, Jon Elson wrote:

> No, I've seen this! The nuts will spin right off the screw, if you hold
> it vertically.
> Unless the preload force is made insanely (and destructively) large, the
> friction
> will still be very small. 500 or 1000 Lbs load on a .875" to 1.25"
> ballscrew
> of 5 TPI is a very small load, as ballnuts this size are often rated for
> 10000
> Lb loads.

Absolutely not !

>From McMasterCarr Catalog 108, Page 946, which gives the specs for Nook

0.004" per foot ballscrews, which have the same loading specs as their
0.001" per foot ballscrews:

Screw size Load Capacity
5/8" 778 pounds
3/4" 1,100 pounds (5 TPI)
1" 1612 (4 TPI)
1 1/2" 4,198 (4 TPI)

None of these ballscrews are rated for 10,000 pounds. Acme screws have
a much, much higher load rating.

> The preload on commercial anti-backlash ballscrews in the 1.25"
> size is normally around 3000 Lbs when new.

No way.

> Modern ballnut design is
> such that the preload is accomplished mostly by stretching the ballscrew
> between the two circuits of balls.

Never. I won't touch this.

> The two ball tracks in the nut are
> ground slightly displaced from the nominal pitch of the screw.
>
> I wish you were closer so I could demonstrate this for you.
>
> Jon
>
>
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Kim Lux <lux@...>