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beanbag
01-05-2011, 04:35 AM
The play I am referring to is when you grab either the inner or outer shell and try to twist it off axis.

I've looked at a few 608 bearings today. Some were designed for skateboards and some were not. All of them had a fair amount of wiggle. The size of this bearing is 8mm ID x 22mm OD x 7mm width.

I have also poked around on some 6000 bearings (10mm x 26mm x 8mm). They don't have any detectable wiggle, yet they are nearly the same size. I know there is a spec for clearance, but this difference seems pretty extreme. Both are deep groove radial bearings, so how can I tell if I buy a radial bearing if it will wiggle or not?

Ian B
01-05-2011, 06:30 AM
The clearance should be shown by the bearing's code - have a look at

http://www.wib-bearings.com/en/tech/tech_06.htm

and

http://www.promshop.info/cataloguespdf/kbc09.pdf

Ian

edward miles
01-05-2011, 06:51 AM
The first consideration for bearing quality and tolerance questions is, who made them. If it is an Asian brand where they make a few small sizes to sell to the cheap market, you can expect anything. If it is a known major brand you can expect products that conform to the specs in their catalogs. Your method of testing for radial clearance is not the same as the manufacturer's. Radial clearance can be tested by clamping the inner ring to a ground steel plate, setup a dial indicator against the outer O.D. and move the outer ring away from the indicator, then back toward the indicator. The movement of the indicator is the radial clearance.

Ed

J Tiers
01-05-2011, 08:51 AM
ALL bearings of that type will "wiggle". it's just how much.

If you want them NOT to wiggle, you need either angular contact type, or tapered roller type.

Standard ball bearings are for radial loads, and "some" axial, amounts varying with unit.

lakeside53
01-05-2011, 11:25 AM
I'll take Jerry's post one further -if you want them not to "wiggle", even with angular contact bearings, you'll need to use preloading - either internal to some multi-row bearings, but more usually by external means.

With radial bearings, a C2 clearance bearing will generally have less "wiggle" than a C3 or "electric motor" quality, but they will still have movement. The bearing clearance ranges overlap though...

Your test with the 6000 bearing - if it's shielded or sealed, the grease can make a big difference with a "hand test". Wash out the grease and try again.

Black_Moons
01-05-2011, 01:25 PM
I thought that wiggle was so you did'nt have to be absolutely perfect in mounting them aligned to eachother. I noticed that while cheap bearings wiggle, they don't tend to have much runout, and are rather solid once you mount two with a shaft through them.