Re: [CAD_CAM_EDM_DRO] Re: What makes a machine CNC ready?

With the "point of contact" reasoning, plain bushings should out-perform any ball bearing. And as long as oil is present, nothing should ever wear out.

Still not convinced there is ever an advantage to using acme screws in a CNC application.

I have one Bridgeport with the original ballscrews in it from 1976.. They are thirty years old. The machine originally came equipped with a Bandit controller. After all the use and abuse the machine still only has .001" backlash on X and Y.. On top of that it spent most of it's life in a carbide tool grinding shop.

Ron



turbulatordude <dave_mucha@...> wrote:

--- In CAD_CAM_EDM_DRO@yahoogroups.com, R Rogers <rogersmach@...> wrote:
>
> Another thing being over-looked is the type of materials for each.
Acme screws are soft and generally not heat-treated at all, ballscrews
are case heat treated to 65-72 rockwell and then precision ground to
tolerance.. Like comparing cold rolled rod and Thompson shafting.
There is no comparison other than they are both round.
>
> Ron
>

But, when you calculate the total surface contact, the 1/8" dia balls
contact the screw and nut on a pad about 0.01" diameter. like using
ice picks as your table legs.

That is why they don't use teflon coated ballscrews.

on an ACME screw, the contact area is an order of magnatude larger, so
the forces per sq in would be comparable if not higher in favor of the
ACME.

And, since wear can only occur when the oil film is not sufficent to
keep the nut and screw from contacting, or if there is debris in the
oil, life of the screw *can* be longer than the ballscrew.

Both screws are engineered for the job. It really boils down to
application.

Dave






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