Re: spinning ball nuts

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "plastiguy" <plastiguy@a...>
wrote:

> OK, new idea for my fast running long axis CNC router. The overall
> travel the long way will be about 100". From all of the mechanical
> calculations to attain the rapid traverse speed I wanted, out

popped

> an unrealistically large diameter lead screw solution (financially
> unrealistic, that is). So, instead of putting in a 1.5" diameter
> screw and spinning the screw, I'm considering a smaller dia.
> stationary screw and then spinning the nut (can go as fast as I

want

> then). Besides the added design challenge of having the servo

motor

> move with the gantry that it drives, what snafus might I encounter
> with this approach? Anyone have any experience using spinning ball
> screw nuts instead of spinning the screw?
> Scott

I have a non-contact table that is similar in length and I came to
the same conclusion. The spinning nut is not hard to do and will
work well. However, it will be rather large and the problem then
comes from the dip in the screw when the machine is at one end.

Also, the screw will need to be tensioned. Check the pressrure one
can use to pull on a ling screw, then push on the screw. My stepper
can create something like 150-200 pounds of force, NEMA-34 single
stack, 1:1 on the screw, 1/2-13 all tread. Theoretically, it is like
535 pounds of force generated in the gearing, but with the loss of
efficiency there is MUCH less delivered. BUT.. and here is the big
but... The 1/2 dia rod will bend with only 14 pounds of force
applied. I can pull over a thousand pounds, but push only 14 with
the small diameter.

My next up-grade will be a single belt. Pulls itself to either end
and can spin faster than a screw.

Dave