Re: Ball screw lead

James,

Actually, "zero" backlash is NOT the advantage of ballscrews...

Tha advantage of ballscrews is their EFFICIENCY. Often in excess of
90 per cent. Acme screws are typically under 50%, with other
threadforms closer to 35%.

Both types have similar backlash. And both types can be ANTI-
"backlashed".

So ballscrews allow you to move the same load with smaller
motors/force, or faster for a given motor/force. This is their
advantage.

There is a commonly held belief that ballscrews are more accurate as
well... Also false. Both ballscrews and other threadfroms are
available in many different quality grades.

One downside of the efficiency of ballscrews is that you
can "backdrive" the ballscrew by pushing on the nut. Although this is
generally bad for our CNC usage; it is wonderful when the power goes
out at the local supermarket because this "downside" lets you open
the automatic doors by pushing on them. (many automatic doors in
stores use ballscrews to actuate them.)

Hope this helps,

Ballendo

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "jamesmcguiness2001"
<jamcg@a...> wrote:

> What am I missing? I realize the advantage of ball screws is
> the "zero" back lash advantage, (much better than the lead screw in
> my cross slide), however how do you get the incremental movement.
>
> On my lathe the cross slide has a .002 per increment and a 40
> increment dial. This means that the distance in one revolution
> is .080. Most of the ball screws I have found THK for example
> have .500 to .200 lead per revolution. Seems like there is a loss
> in incremental movement.
>
> Please help a beginner.
> Thanks and Regards
> James McGuiness