Re: spinning ball nuts

How fast are you planning on going?

What is the weight of the gantry?

What size screw did you determine will work?

What size motor are you gonna use?

Stepper or Servo?

Single screw or dual?

The devil is in the details…

Just so you know, the minute you said 100" (IMHO) fixing the screw
was the best option. Rotational Inertia of a 100" screw will kill
your numbers.

My two cents would recommend dual 3/4 screws with encoders mounted on
the ballnut. Guessing that your gantry is of a decent weight you
could go with a pair of 120 watt servos (depending on what you're
cutting). You'll want to reduce them 2 or 3 to 1 just to get the
reflected inertia under control and so you can really wind them up
well.

Good Luck.

Thanks
Aaron Moss
www.IndustrialHobbies.com


--- 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