Re: [CAD_CAM_EDM_DRO] B/S vs. acme was Re: What makes a machine CNC ready?

>R Rogers wrote:
>
>
> /// So if someone building a linear CNC device has the choice between the two, sometimes it's an "advantage" to use an ACME screw over a ballscrew? When? Other than cost and availablitly, I can't think of any.
>
>
>
>
>

Well, I built a laser photoplotter that has a laser-writing carriage
driven by a stepper motor.
it travels at 10 steps/second, with each step = 0.001" at a continuous
rate during the image
generation. I used one of those cheap black Thompson screws first, and
it proved the concept,
but thread "drunkenness" ans backlash caused image artifacts. I then
replaced the screw
with a Kerk selected precision screw with the automatic plastic
anti-backlash nut, and it works
VERY well. It has zero backlash, and even .001" backlash would show up
clearly in the plots.

This isn't a typical CNC application, but it comes pretty close. It
also isn't an Acme screw, but
it is a friction-type screw and nut system, with two plastic nuts
preloaded against each other.
There is a self-adjusting mechanism between the two nuts to prevent the
preload from
getting too high.

I think these Kerk screw/nut assemblies work quite well for low-load and
moderate speed
applications. And, the Kerk set cost almost 10 x more than the cheap
ballscrew, but performs
much better.

Jon