Re: [CAD_CAM_EDM_DRO] Rotating Ballnut

vrsculptor wrote:

>Long ballscrews tend to whip at higher RPMs. The longer the screw
>the larger the reqired diameter. I can't afford a large enough
>diameter rotating ballscew for a router to eliminate whip at planned
>RPM's with a 96 inch span. An alternative is to use a smaller
>ballscrew and a rotating ballnut supported between bearings.
>
>Would I be correct if I assumed that the diameter of a ballscrew
>with a rotating ballnut is only dependent on the required dynamic
>load? If I needed less than 800 pounds of thrust could I get by with
>a 5/8 ballscrew (rated at about 800 pounds) 96 inches long? Mcmaster
>has 5/8 ballscrews for $1.27 an inch. One inch (rated at 3,700
>pounds) is $2.70 an inch.
>
>Am I missing something?
>
>

Yes, you really don't want to put an 8 foot ballscrew in compressive load.
It is bound to bow. If you can keep it in tension above the maximum
thrust, then it should work. But, that means a constant 800 Lb load on your
router frame. If it can handle it, then everything should be fine.

A secondary concern is the helix angle changes with different screw
diameters.
I'm not sure if this is a problem in this application of not. But, the
helix gets
steeper as the screw diameter gets smaller.

Jon