Re: [CAD_CAM_EDM_DRO] Ball-screws

James Owens wrote:

> Hi Jon,
>
> I take your points and as usual you are perfectly correct.
>
> These are rolled threads and are not anti-backlash nuts but the idea
> was
> just to buy the thread and make up my own ends. I say the machine is
> Bridgeport like, it is in fact, a Beaver and I doubt if the Bridgeport
> kits
> will fit with out a great deal of work.

Some outfits have kits for a variety of machines, not just true
Bridgeports.

> The cost of the nuts on the cheaper option from McMaster-Carr is only
> $32.00
> and I thought that if I bought two for each axis I could make up an
> anti-backlash nut.
>
> Surely if the error is known it can be programmed out by the
> controller or
> the CAD/CAM package, or even me as I do the drawing.

This is a common misconception. Yes, for positioning only operation,
the error can be compensated for. But, for contouring and milling
of surfaces, it takes the CNC system a finite time to get from one
side of the backlash to the other, and so the table is uncontrolled
for a moment. This leaves bumps and gouges on surfaces that
are supposed to be smooth. Yes, in theory, you can make up
an anti-backlash nut yourself. I would think that pinning the
two nuts together with 2 dowels, such that the dowels are locked
in one nut's bracket, but free to slide on the other one, and then
providing a couple Belleville washers or some other spring
mechanism ought to work.

Jon