Re: [CAD_CAM_EDM_DRO] Re: GEM-500PCN bedmill

Not being a bearing manufacturer I can only guess!
The hand etching and machine marking might be done after
the selection process.

As far as the bearing retainers... My catalogs show a variety
of retainers available for all grades. It might be that higher
speed retainers are seen more in higher grade bearings
simply because they are used more.

I have also heard that class abec 7 and 9 are picked, not made. If the
control limits were abec 1 and 7 then xbar
would need to be about abec 5. But then they would still have
to be 100% inspected to retrieve the higher grades. More
likely a whole batch will sometimes come in at very high grade
so a sampling plan might be used to catch that.

I can say that of the last 30 or so FAG 7205 ABEC-1 bearings I got ALL of
them were ABEC-3 or better as far as runout...
I indicated them. That is why I picked that brand... they do not make 3's
and 5's anymore I was told. Not statistically significant though... another
batch might be much poorer.

But I have always been amazed that I can buy an abec 1
bearing accurate to four tenths TIR for a couple bucks. I honestly have no
idea how they can do that.

Leslie Watts
L M Watts Furniture
Tiger, Georgia USA
http://www.rabun.net/~leswatts/wattsfurniturewp.html

----- Original Message -----
From: <dougrasmussen@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Friday, May 25, 2001 1:41 PM
Subject: [CAD_CAM_EDM_DRO] Re: GEM-500PCN bedmill <bearing grades>


> 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
>
>
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