Re: What makes a machine CNC ready?

> --- In CAD_CAM_EDM_DRO@yahoogroups.com, Tony Jeffree <tony@...>
> wrote:
> >
> > At 18:38 27/06/2006, you wrote:
> > >This is an article of mine that appeared in the Digital Machinist,
> > >special edition of Home Shop Machinist.
> >
> > Fred -
> >
> > Nice article, but I think you exaggerate the efficiency of the
> typical Acme
> > screw by a factor of around 2. The figures I have seen quoted are
> in the
> > 20-40% range, not 60-70% as you state.
>
> Efficiency depends on the material of the nut and the surface
> treatment of the screw and it also varies with the screw lead.
>
> http://www.kerkmotion.com/pdf/kerk-catalog-2005.pdf
>
> See page 18, 1/2-.2 lead through 1/2-.4 lead acme threads are .63%-
> 76% efficient.
>
> What is highly exaggerated by the uninformed, is the utility of
> rolled ballscrews compared to precision acme screws. "What does
> that crunching sound mean?"
>
> Fred Smith - IMService

The case quoted above is not an average Acme thread effeciency.
These are special Acme screws with turcite coating that it warns about using in enviroments where lubrication and coolant is banned and has low friction polimer nuts.
You are comparing apples to oranges.
Cost wise these screws are also higher than rolled ball screws from a reputable supplier.

John S.