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A while ago, I started buying and fixing used bikes and parts.

As a result, I have quite a large number of old individual wheels lying around, most of them with bearings that are no longer good. Since it's typically the cones that give out first (by design, if I understand correctly), one could of course replace the cones. Those do cost a bit, though. But most of all, I like repairing things whenever I can, rather than replacing them.

So here's my question: Would it be possible and sensible to machine the bearing race of the cone, rather than replacing the cone?

I assume that 0.1 or 0.2mm (up to 8 thousands of an inch) should do to get a nice surface, and that this should not be a problem for the overall geometry.
Would you say that is about correct, or am I overlooking something?

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  • I would first consider using some sort of abrasive approach. Jul 28, 2022 at 21:06
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    I have cones and a lathe - might give this a try.
    – Criggie
    Jul 29, 2022 at 1:08
  • i'm really looking forward to your findings, @Criggie !
    – Burki
    Aug 1, 2022 at 20:35

1 Answer 1

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The surfaces of cones are hardened, so you're not going to be able to do it on a lathe with typical tools (maybe with tungsten carbide tools). However people do grind cones to resurface them, finishing with a polish. The link describes locking the cone onto an axle and putting it in a drill press (a lathe would also work) then running an grinder or large dremel with an abrasive disc or cone. In some cases a thin hard layer is removed and they then wear fast, but others are hard enough below the surface to work well.

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    Many recent Shimano cones are coated with a layer of cubic boron nitride. If resurfacing, this layer won't be there anymore, and thus you can't expect to get a good wear life out of it.
    – juhist
    Jul 28, 2022 at 15:35
  • @juhist it's interesting that while Shimano's designs seem quite traditional, their materials aren't. It's also interesting that these (presumably expensive) cones, like cheap surface-hardened ones, won't resurface well, while others are hardened throughout (or at least deeper). I'm not sure how a thin layer of cubic boron nitride would grind, but in bulk it would be a chore. Hopefully the OP is fixing up quite old stuff
    – Chris H
    Jul 28, 2022 at 15:44
  • I suspect the reason for using cubic boron nitride is that today QR axles are gone and it's all thru-axle. Shimano's cup and cone design require a separate axle around the 12mm thru-axle, and the cassette freehub sets a limit to the outside diameter of the bearing. Hence you can't anymore use 1/4" bearing balls as used to be customary for rear, and can't use 3/16" as the next best size after 1/4", but have to go all the way to 5/32". The surface pressure on those 5/32" balls is terrible, and would probably wear out normal cones quite fast.
    – juhist
    Jul 28, 2022 at 16:47
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    @juhist all my bikes are QR or use old fashioned nuts, so I've never worked on a thru axle hub. It doesn't sound good
    – Chris H
    Jul 28, 2022 at 18:26
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    Thank you, and thank you for the link. i'll give it a try then. I can always throw them away if it doen't work out.
    – Burki
    Aug 1, 2022 at 6:44

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