Re: [CAD_CAM_EDM_DRO] Re: skate bearings

On Wednesday 17 August 2005 10:17 pm, Chris Horne wrote:

> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Roy J. Tellason"
> <rtellason@b...> wrote:
> > On Tuesday 16 August 2005 11:41 pm, Tony Smith wrote:
> > > > Is there any reason you have to use skate bearings? Why don't
> > > > you just get some that are an exact match to what you need?
> > > >
> > > > Jeff
> > >
> > > Skate bearing (608s) are cheap and easily purchased. A lot of
> > > motors (vacuum cleaners and the like) also use them. The other common
> > > one is the 607, a little bit smaller than the 608.
> >
> > What do these numbers refer to?
>
> Others have commented on bearings but you might find these links
> useful...
> my first job on leaving school in 197x was with a bearing
> distributor, it doesn't mean I know any more about them, just that I
> know a good value for money bearing when I see it.
> in those days skates didn't have decent bearings so there was no
> supply of cheap good stuff.
>
> The numbers quoted above are the size codes

Ah, in mm, then?

> see http://www.smb-bearings.co.uk/S_MMET.htm for examples
>
> the ABEC numbers are just manufacturing tolerances..
>
> if you want to know more about them then have a look at
>
> http://www.consbrgs.com/technicaldata/380_br.html
>
> and the pages that that page refers to..

*Lots* of stuff on that menu!

> AFAIK ABEC 9 should be OK up to 40,000 rpm or more
> provided they are made of good quality materials, and note
> that the ABEC rating does not indicate the materials, just the
> manufacturing tolerance

Nice to know.

> The reason I and others use the skate bearing is that they are
> ridiculously cheap compared to others and this is directly due to
> them being manufactured in massive quantities for skates..
> simply economy of scale.

I'd heard mention of using skate bearings before, in a number of places. The
design I'm thinking about at this point in time is one where you'd have two
pair of bearings mounted to a bit of angle, and that whole mess riding on a
rod. I have some nice rod here salvaged from old printers, probably long
enough for the sort of machine I'm considering to start with, I just need
some bearings for the purpose. So the high RPM figures wouldn't apply there.

As it turns out, I did stop at a place that I guess passes locally for a
"skate shop", and they did have a case of bearings there. What the guy
there told me was that most of them in that case were for skateboards. I
noticed ABEC ratings from 5 to about 9, with prices correspongingly higher.
The better ones were up over $100 a box, but ones that he said were "okay
quality" and which were marked ABEC 6 if I recall right were only around $15
a box. This is still somewhat more than I'd expected, but maybe I'm
mis-remembering what I thought somebody wrote. They even had some in there
that were some kind of ceramic material, but those were also pretty
expensive.

As it is I'm looking at three boxes or so, plus some angle, and there's
money I don't have to spend at this point in time. But at least I know where
I can find them now.

Thanks for the useful links.