Yeah yeah, I know there’s a similar thread out there. But I have some ideas that I’d like to put into its own thread. This about to get ranty.
Firstly, my conclusion is that ABEC rating is nearly meaningless to us. Note that an ABEC-1 rating indicates a deviation of 10 microns across a 20mm span.
I’ve seen a lot of buzz words thrown out there, ABEC rating, skate rating, contact vs non contact seals… the list goes on. What I’m most interested in is the clearance rating of bearings, which I haven’t seen discussed before here.
Let’s compare the ABEC rating system to the Clearance Rating system.
The clearance rating system is exactly what it sounds like, it’s the overall slop in the system. Generally, there is one value attributed to deep groove ball bearings, and that’s the amount of gap remaining on one side when the inner race is loaded to one side. (there is additionally a value for axial loads, but that is also dependant on specific bearing geometry.)
The scale ranges from C2, CN, C3, C3 and C5.
CN is considered a nominal bearing. Chances are most generic NSK bearings will fit this spec if not otherwise specified.
For a 8mm bore bearing, CN values range from 2 to 13 micrometers. For reference, an abec-3 rating indicates a dimensional accuracy of -8 microns. Interestingly, the ABEC scale doesn’t denote what the nominal value should be, assuming that there is already an included clearance value for said bearing.
Basically, what I’m trying to get at is that the ABEC scale is a rating of how close a bearing is to spec, but it doesn’t denote what that spec actually is! The clerance rating denotes specifically denotes what the accaptable range is for each spec.
Now onto the meat of what I am interested in talking about. The skate bearings we use seem incredibly sloppy, as if the clearance rating is quite high. That’s not necessarily a bad thing, because a higher amount of slop in the system means the bearings can take additional impact and shock loads. However, I’m unsure of how it affects axial loads. Nearly every skate bearing we see has non-contact rubber seals. This means that it’s entirely possible for dust and gunk to get inside the bearings (which we know happens).
Is the high clearance rating specifically to address that issue of foreign debris inside the bearing? Having clearance prevents the bearings from locking up. I believe that it would be a BAD idea to use a low clearance bearing with non-contact seals.
So what about contact seals? Should the bearings have high clearance? Can skateboarding even be defined as “high impact” when we’re using soft urethane wheels, sometimes pnuematic? For reference, the document I’ve been reading uses railroad wheels as an example of high impact, specifically because it’s metal on metal with no give.
What’s even more interesting is that bearings that are press-fit into features are supposed to have MORE clearance, and that bearings that are loose in their housings or shaft generally have NO clearance (A C2 rating, 0 - 7 microns of radial clearance for an 8mm bearing)
In my mind, a proper skate bearing would have full rubber seals and a C2 rating due to lack of dust ingress and loose fits inside wheels and on our shafts. That said, things may change when using precision shoulder bolts, or bearing spacers so you can lock down the inner race location.
ok you’re hired