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Old 2019-03-22, 01:49 PM   #16
mowcius
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Quote:
Originally Posted by mrfixit View Post
I also found something called KRIS HOLM KH ISIS MOMENT HUB Bearing Set from RCbearings , available at RCbearings or Amazon that's NOT the correct 42 x22x12 MM bearing size, so stay away from this. I think he said they were 20mm ones.
Yeah, 20x42x12 is a far more common size. Plenty of bearings around designed to fit 20mm shafts.
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Old 2019-03-22, 05:46 PM   #17
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Originally Posted by mowcius View Post
Yeah, 20x42x12 is a far more common size. Plenty of bearings around designed to fit 20mm shafts.
I AM NOT recommending this but if 22x42x12 bearings are non-standard and suddenly become unobtainium, no can getz, and if 20x42x12 bearings are in reliable, standard supply then a machinist could chuck a 22mm axle into a lathe and turn the axle diameter down to 20mm in order to use the 20x42x12 bearings. Of course, reducing the axle diameter reduces the strength of the axle and also reduces the strength of the ISIS connection fitting which is why I do not recommend doing this but I am posting this here just as a future reference in case of a bearing emergency situation, possibly months or years from now. BTW, altering the inside diameter of a bearing would be a challenging thing to do, at least, and would introduce its own structural strength concerns, too.

And yes, I find this bearing discussion both interesting and quite worthwhile, gotta have bearings as they are not optional, thank you!

Last edited by Go Uni; 2019-03-22 at 05:51 PM.
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Old 2019-03-22, 09:47 PM   #18
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Originally Posted by mrfixit View Post
Definitely a non standard bearing. Cut....

Maybe someone who has some 42 22 12 unicycle.com bearings can post a pic here of the bearings, with the part numbers shown. That might be useful to find more sources, too.

I also found something called KRIS HOLM KH ISIS MOMENT HUB Bearing Set from RCbearings , available at RCbearings or Amazon that's NOT the correct 42 x22x12 MM bearing size, so stay away from this. I think he said they were 20mm ones.

And I'm sure the pictures aren't the actual bearing in most listings.
Here is an ISIS bearing. The numbers/ID are not standard either.


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Old 2019-03-23, 01:56 AM   #19
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Or you could get BMX 22mm Mid bottom bracket bearings, and use a .5mm spacer made from shim stock. These bearings are 41mm O.D.

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Old 2019-03-23, 03:11 AM   #20
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It looks like the mid bearings are 11mm’s wide, so it would also need a 1mm spacer.
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Old 2019-03-23, 05:16 AM   #21
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Here is an ISIS bearing. The numbers/ID are not standard either.


Jim
Based on what I can see in the picture, by eyeball examination, it looks like there is enough "extra" metal so that the axle diameter could be reduced by 2mm without taking any metal away from the axle's ISIS connection fitting, so apparently that consideration could be ignored. Reducing the axle diameter from 22mm to 20mm is somewhat of a strength gamble but engineering also includes what is known as a safety factor, that in this situation an engineer might have considered the strength and weight of a human gorilla and then have based their design on that, so that removal of 2mm here might not be too much of a gamble, but please note my use of the words "might not".
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Old 2019-03-23, 05:48 AM   #22
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Originally Posted by Go Uni View Post
Based on what I can see in the picture, by eyeball examination, it looks like there is enough "extra" metal so that the axle diameter could be reduced by 2mm without taking any metal away from the axle's ISIS connection fitting, so apparently that consideration could be ignored. Reducing the axle diameter from 22mm to 20mm is somewhat of a strength gamble but engineering also includes what is known as a safety factor, that in this situation an engineer might have considered the strength and weight of a human gorilla and then have based their design on that, so that removal of 2mm here might not be too much of a gamble, but please note my use of the words "might not".
The out side diameter of the spline is 21.2mm, so turning the spline and shaft down to 20mm would sacrifice some strength in the spline as well as the shaft.
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Old 2019-03-23, 05:53 AM   #23
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Originally Posted by Go Uni View Post
Based on what I can see in the picture, by eyeball examination, it looks like there is enough "extra" metal so that the axle diameter could be reduced by 2mm without taking any metal away from the axle's ISIS connection fitting, so apparently that consideration could be ignored.
That last 2 mm has a radius where it comes off the spline. Without it there would be a sharp corner which would focus the stress. The result would be dramatically weaker.

The ultimate strength isn't just about the amount of material. The geometry of transitions can be more important.
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Old 2019-03-23, 06:36 AM   #24
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The out side diameter of the spline is 21.2mm, so turning the spline and shaft down to 20mm would sacrifice some strength in the spline as well as the shaft.
OK, I was interested in that but relative to the inside diameter of the bearing the spline outside diameter just looked smaller than it actually is.
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Old 2019-03-23, 06:49 AM   #25
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That last 2 mm has a radius where it comes off the spline. Without it there would be a sharp corner which would focus the stress. The result would be dramatically weaker.
I can see that and for the same reason as you mentioned I would not change it but it just looked like there was more diameter metal available. Apparently pictures have limits for me.
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Old 2019-03-23, 07:59 AM   #26
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Ah, time out for coffee.

What I find curious is why the need for an expensive to develop non-standard bearing. A designer could know what size of bearing they need but then as is commonly done search for a standard bearing of the same or slightly larger size and then make adjustments to their design if need be. Sure, there are situations where nothing but an exact design match will do, but for a unicycle? ISIS is a great system but consumers now have only one source for bearings. Oh well, Schwinn used to routinely do that sort of thing with its bicycle tires.
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Old 2019-03-23, 09:01 AM   #27
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What I find curious is why the need for an expensive to develop non-standard bearing. A designer could know what size of bearing they need but then as is commonly done search for a standard bearing of the same or slightly larger size and then make adjustments to their design if need be. Sure, there are situations where nothing but an exact design match will do, but for a unicycle? ISIS is a great system but consumers now have only one source for bearings. Oh well, Schwinn used to routinely do that sort of thing with its bicycle tires.
Probably because it's the cheapest method overall as a OEM. It's just having the bearing supplier turn 1mm more of the radius of a 6004 series bearing. If you go with a 6005, your outside diameter changes 5mm, so you might not be able to use the same machined bearing cap parts as with square taper bearings, the use of shims to convert between the two is made impossible too. I'd guess that previous onza and other outdated splines used 42 mm outside diameter, and 12 mm wide bearings too, so you would want to keep that compatability.

If you go large on the inner diameter, you are throwing compatibility to the previous frames away. You also have to get larger round stock, and machine more of it to get your Isis spline, and to keep similar weight. Machine time is very expensive, for the bearing manufacturer turning 2mm more of the inner diameter is a lot less machine time that for the hub manufacturer to turn the 30mm stock you need to get a 6005 bearing on there down to 21.2 mm for the Isis spline.

Most unicycles never get a bearing replaced, so the aftermarket supply being limited is pretty irrelevant.

That's my analysis at least.
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Old 2019-03-23, 01:07 PM   #28
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What I find curious is why the need for an expensive to develop non-standard bearing.
Nothing compared to why anyone would be concerned about whether a bearing that doesn't often need to be replaced costs $10 or $20 on a $500+ machine.

Also remember that the ISIS standard was developed for bicycles. The engineers who put it into unicycles didn't have carte blank as the starting point.
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Old 2019-03-23, 08:37 PM   #29
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I think you all are getting a little carried away with your talk about machining spindles down because UDC bearings might disappear. I see them on the QU-AX web site, and probably any manufacturer of ISIS hubs sells them as replacement parts.

And they might be "non-standard" but that doesn't mean you would have to find somebody to custom make one for you. Alibaba showed several Chinese manufacturers selling them cheap. No idea what the shipping would be but you could probably get a lifetime supply for all your unis for the price of having an axle machined. For example here and here.
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Old 2019-03-23, 09:01 PM   #30
mowcius
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I suspect that we'll all die due to climate change before ISIS spindle bearings become completely unavailable.

I think I've replaced two sets of bearings on all of my unicycles in around 9 years, so with the number I've got spare, I'm probably set for life!
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