Re: GEM-500PCN bedmill

Les,

Thanks for the post, very informative.

Here's something you may know....I've heard people say that ALL
bearings are made the same, and those that test as higher accuracy
are set aside and sold accordingly. So, for instance, out of a run
of 100 ABEC 1's, you might get three ABEC 7's.

I don't believe that since the higher precision bearings I've handled
have totally different ball retainers. Besides the retainers, the
higher accuracy ones are hand etched while the lower grades are
machine marked.

Any thoughts on this?

thanks,

Doug

--- In CAD_CAM_EDM_DRO@y..., "Les Watts" <leswatts@r...> wrote:
> Doug is correct on the bearing grade thing. The specs are
different.
>
> The difference is between the american ABEC and
> ISO/DIN.
>
> It often confuses me when manufacturers just give a number
> without mentioning the spec type.
>
> From the SKF catalog:
>
> ABEC-1 = ISO class 0
> ABEC-3 = ISO class 6
> ABEC-5 = ISO class 5
> ABEC-7 = ISO class 4
>
> (hope I got that right)
>
> Electric motor bearings are usually ABEC-1/ISO 0
> While the lowest precision class, these bearings are good to tenths
in
> smaller sizes.
>
> Many ballscrew and lead screw end bearings are ABEC-1/ISO 0 as well.
>
> Spindles these days are usually ABEC-7/ISO4 or better.
> Many distributors do not carry the intermediate grades anymore-
they go
> right from ABEC-1 to ABEC -7 or 9.
> This might be a good thing because with some manufacturers
> as most ABEC-1 bearings could be ABEC-3 or better. The
distribution might
> be centered near there. I suspect ABEC-1
> and ABEC-7 are about 3 sigma in the spread. I can't prove this
though... my
> data is not statistically significant. But it would explain the
high cost of
> ABEC--7+... perhaps only 3%
> of the production is that good.
>
> Some spindles are made with preloaded ABEC-1/ISO 0
> (the lowest class) and the tapers etc are machined in place
> after the bearings are mounted. These are usually referred to as
> "cartridges"-- when worn the whole assembly is tossed
> because the bearings cannot be replaced without remachining it. But
you can
> get extreme accuracy with lower grade bearings. The grade has
nothing to do
> with "slop" in a preloaded bearing.
>
> They higher accuracy grades usually have higher speed ratings as
well. Their
> price can be ten times that of an ABEC-1/ISO 0. Extremely close
shaft and
> housing fits must be
> performed to use the greater accuracy of these bearings.
> They are also aligned circumferentially with a high spot mark.
>
> For ballscrew nuts radial runout is less an issue but internal
> clearance is. In both ballnut and shaft bearings these are
designated by a c
> prefix. It goes from c1 to c5 usually and
> unmarked bearings are typically c3.
> More typically important is pitch accuracy (e300) and preload
> amount and variation with ballscrew assemblies. Preloaded
> ballscrews have no internal clearance and as such do not use the c__
> specification from what I see.
>
> Inch size and Tapered roller bearings have a different
classification
> system... I won't go into that because I don't know it well. I have
to
> really dig to spec them.
>
> Leslie Watts
> L M Watts Furniture
> Tiger, Georgia USA
> http://www.rabun.net/~leswatts/wattsfurniturewp.html
> ----- Original Message -----
> From: <dougrasmussen@c...>
> To: <CAD_CAM_EDM_DRO@y...>
> Sent: Friday, May 25, 2001 12:14 AM
> Subject: [CAD_CAM_EDM_DRO] Re: GEM-500PCN bedmill - CNC ready
>
>
> > Ballendo & Smoke,
> >
> > I think the specs said grade 5 "ball screws" not bearings. I
don't
> > know what that means, is there a system for rating the relative
> > accuracy of ball screws?
> >
> > Incidently, I once had to get some precision bearings that were
made
> > in Germany. As I recall the grading system was the opposite of
> > ours, with the lower numbers meaning higher precision.
> >
> > Doug