Re: [CAD_CAM_EDM_DRO] Re: 1st dumb Question: Ball Screws

jeffdavis516 wrote:

> Yes you are correct that other screws can be as accurate. You know
> if you quit sleeping in past 9:00 AM you can beat my answering :)
> Course with 65 + groups you read It's a wonder you sleep at all.
>
> Jeff
>
> --- In CAD_CAM_EDM_DRO@y..., "ballendo" <ballendo@y...> wrote:
> > Jeff,
> >
> > Sorry but I have to disagree. Positional accuracy is not inherently
> > better with ballscrews. But you are spot on in saying that "Your
> > application will dictate your need."

Acme screws can be accurate, but if fitted with tight anti-backlash
nuts, they will wear quicky. Once an Acme screw has a worn spot,
the anti-backlash nuts can't be tightened fully at that spot, and so
you get backlash there. Acme screws wear anyway, even with normal
nuts, and become innacurate in the worn region.

Ballscrews wear at a rate of about 1/1000 th that of Acme screws, and
so very high nut preload can be maintained without excessive friction
or wear. Ballscrews can also deliver astounding linear force without
significant change in friction, while Acme and other screw designs
suffer from the usual sliding friction equation, with friction proportional
to load. This friction can also cause heating of the screw during
rapid and sustained movement, causing further inaccuracy.

I just can't imagine trying to build an accurate CNC milling or turning
machine without ballscrews. CNC routers are another matter, where
linear motion drive without a screw is usually the preferred method.

Jon