Re: [CAD_CAM_EDM_DRO] Bent Nook ballscrews ?????

Kim Lux wrote:

>There is where you are wrong. Do this: set up 2 ballnuts with a 500
>pound spring between them. Do they freewheel on the ballscrew or do
>they stick ? (They will stick because of the friction of the 500 pound
>load.) Now add a 500 pound cutting load. The total load on the ball
>screw is 1000 pounds between the the two ballnuts, 500 pounds from the
>cutting and another 500 pounds from the preload.
>
>
>

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. The preload on commercial anti-backlash ballscrews in the 1.25"
size is normally around 3000 Lbs when new. Modern ballnut design is
such that the preload is accomplished mostly by stretching the ballscrew
between the two circuits of balls. 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