The truth about skateboard ball bearings

[Swede]

Sorry, no I don't have the truth, but I AM still looking. The "Truth" I seek (sounds vaguely Zen like) is this: Are those oh-so-cheap "ABEC-7" skateboard bearings that you can find in nearly any sporting-goods store REALLY ABEC-7? I get this weird vibe that it is all B.S. and is simply technobabble designed to get some teenager to part company with his $$.

A pack of 10 ABEC-7 metric bearings goes for $29 at our local Oshman's sporting goods store. The same ABEC-7 bearing from Boca Bearing online goes for $16 apiece. If truly ABEC-7, they'd be a great source for ways and lightly loaded ballscrews.

I know this is nothing new, and guys have been using skate bearings for years for CNC projects, but does anyone know if they are genuinely ABEC-7? Any way to actually test them? If one has a set of pin guages, and a good mike, one could check them dimensionally, but the dynamic aspects of the radial bearing is tougher to check.

[kong]

Funny you should bring this one up, I am in need of some 8mm id bearings, and they are seemingly difficult to find over here, so I was considering using skate bearings for my leadscrew ends. I will be interested in your findings! The thing is, I take it they won't stand a lot of axial force, so I'll probably use as many bearings as I can squeeze on the end of the screw.

[HuFlungDung]

What is the radial clearance of these skate bearings? Are they really wobble free?

[kong]

A quick google to understand what you are on about Hu, revelaed a supplier of "your average skate bearing". The info on the site claimed a radial clearance of "C5" or 0.0005 - 0.0008".

[Ferenczyg]

Well, the only things I could state are:

1.- all the skating ballbearings I've seen show 608Z or 608ZZ and the ABEC rating on the flange, so the rating is from factory not from packager.
2.- I've never seen ABEC bearings on a sports store over ABEC-5, but this can be a local issue
3.- ABEC-3 are about 1$ the piece, ABEC-5 about 1.5 $ the piece, at least where I've seen
4.- Answering Hu, yes, they are absolutely wobble free, but absolutely only means 'as far as I can measure'

And if I am not in a mistake, If they say are ABEC-X and sell as ABEC-X but they're not ABEC-X, you can sue them..

Fer

[HuFlungDung]

C5 clearance is quite a bit. Most electric motors use a C3 clearance, and they are fairly loose, that is, you can make the inner race wobble quite a bit, yet the bearing is considered perfectly okay. This design is so it can run hot and not self destruct.

So depending on what kind of load you want your skate bearing to carry, it may or may not be what a person would want.

[buscht]

Here's an example.
http://cgi.ebay.com/ws/eBayISAPI.dll...671672169&rd=1

[ESjaavik]

I don't think the biggest problem will be the bearing. My Bulgarian made crapbox of a woodworking machine uses ball bearings on a steel rod for its table movement. They are arranged in a triangle and there are one suchsetup at each end. They have in a short time worn down into the steel rod and rides like on a bumpy road, binding even on the smallest speck of dirt. So at least 2 things are obvious to me:

They need to be totally enclosed, and have felt wipers at both ends.

They need to run against a flat, not a round rod.

The ways they run on need to be case hardened. But my hardening furnace can only take objects up to 50cm, so I can't do itmyself. The rods are supported at 2 places each, so a through hardened rod would not be a good idea. I checked the price of square rod 30x30mm in semi-hard carbon steel too, and it is not cheap! So I may try PTFE pads riding on the current slides. Or ballslides from eBay. I've seen them at prices below the just mentioned rod. Especially when someone offers slide without blocks, they go for almost nothing. Very few take the chance they can get matching blocks for a good price.

Kong: What you need for the ballscrew ends are angle contact bearings, or if you don't run them at high speed use ball thrust bearings. They can't be used at high RPM because the centrifugal forces will make the bearing bind. Bicycles use angle contact bearings at several places, maybe they couldbe a source of cheap bearings?

[John S.]

Don't get confused by the term ABEC
There is the standard ABEC and there is Acme Bearing Exporters, China

[InventIt]

Originally posted by John S. Don't get confused by the term ABEC There is the standard ABEC and there is Acme Bearing Exporters, China

That's funny!
I remember a teacher in high school, many years ago, telling us how Japan renamed one of it's citys to "usa" This way they could stamp "Made in usa" all over every peice of junk they exported over here. I don't know honestly if that's true, but I do remember the teacher saying it.

[JFettig]

I skated for a little while, and I beleve these abec ratings are correct, That is how good they are as you get them, you get what you pay for though, you buy cheap abec 7 bearings, they dont last long, I have a friend who has gone through like 20 in about 2 years of skating.

and yes, there are Abec 7, I have heard of abec 11 bearings too.

"Don't get confused by the term ABEC
There is the standard ABEC and there is Acme Bearing Exporters, China" lol thats a great one.

skate bearings in this application are probably very promicing, if you get good ones you wont have any slop in them.

Jon

[Ferenczyg]

Ok, but really we are not underestimating the fact that the abuse we will put on the bearings on a diy cnc are much less than the abuse put on them when skating? So this seems to me at least..

Fer