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PostPosted: Sat Mar 31, 2012 2:56 pm 
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I have been playing with the idea of making some new cranks for some time now.

See: http://weightweenies.starbike.com/forum/viewtopic.php?f=3&t=96497&p=819164&hilit=pushed+cranks+space#p819164

After a few beers with an engineer friend of mine today, I decided to put something together. The moulds seem to be cheaper than those for a frame so hopefully won't tap into grocery money.

In fact I already have a few ideas bouncing in my head, but then I discovered to my dismay that I do not know anything about bearing standards at all.

Therefore, I'd appreciate any pointers in that area.

To be more specific, I am trying to figure out what is the thinnest bearing that will fit a PF30 (ID 46mm) shell (to find out what size spindle can go through). GOing to a bigger frame BB standard will be a much bigger undertaking.

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Posted: Sat Mar 31, 2012 2:56 pm 


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PostPosted: Sat Mar 31, 2012 3:11 pm 
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47x35 (6807) ball bearing
42x35 (HK3516) needle bearing

As the needle bearing is not really an option, I would try to gain a mm in the BB shell to use the 6807 bearing

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PostPosted: Sat Mar 31, 2012 4:36 pm 
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Thanks, what do you exactly mean by "gain"? TO file some material out of an existing frame?

If this means the frame can't go back to fitting regular PF30 BB, then I might as well go with a bigger BB shell in the frame.

Epic-o wrote:
47x35 (6807) ball bearing
42x35 (HK3516) needle bearing

As the needle bearing is not really an option, I would try to gain a mm in the BB shell to use the 6807 bearing

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PostPosted: Sat Mar 31, 2012 4:44 pm 
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Yes, you will need some sort of spacer to be able to fit regular PF30.

I haven't seen any crankset that uses needle bearings but it can be a good solution. The main problem is that it weighs 10gr more than a roller one.

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PostPosted: Mon Apr 02, 2012 2:00 am 
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i'd go with a needle bearing on the drive side and a radial or deep groove bearing on the left side. better load capacity on the higher loaded side, with side load management done by the left bearing. but that's just me.
i personally wouldnt bother making something bigger than 30mm, i would focus on improvements elsewhere.
might want to check out what Praxis is using on their 35mm spindle. probably the 47mm od bearing, which is why theirs is outboard.

another idea is, going with the 35mm spindle, mount the needle bearing inboard but the left radial bearing outboard. that's the way sweet wings cranks did it in the distant past. with the right bearing inboard, it leaves you the room to have the spider. if right spider width=left outboard cup width, that would be very convenient for symmetry.


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Posted: Mon Apr 02, 2012 2:00 am 


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PostPosted: Mon Apr 02, 2012 7:20 am 
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Thanks for your suggestions. I am currently pondering over a carbon spindle so it will definitely have to be bigger than 30. Frankly 30 simply isn't a good size for carbon spindle.

Here is the engineering question -- right now, several parts are jammed in a small cluster, to make everything work, something will have to give. Easiest way is to squeeze the crank arms (then you can have enough room to do outboard, BB86, etc.); if you don't want to squeeze the crank arms, then you would have a huge Q factor, which isn't great; then you could also squeeze the spindle, 24mm, etc., which again, not great for carbon; then you could also squeeze the bearings (apparently not much room to squeeze, plus durability is down the drain).

Here is my problem -- I don't want to give up any of those, which is pushing me towards enlarging the BB shell like Look did, which creates all sorts of compatibility issues, plus the retro types will have a field day.

Eric -- if we are talking about adaptors, then I might just bite the bullet and create something along the lines of the LOOK Zed -- bigger frame shell, and bigger spindle. Therefore, I am hoping for a magic bearing that will fit 46mm BB shell and 35~40mm spindle. If not, then I will have to go back to the drawing board.



thisisatest wrote:
i'd go with a needle bearing on the drive side and a radial or deep groove bearing on the left side. better load capacity on the higher loaded side, with side load management done by the left bearing. but that's just me.
i personally wouldnt bother making something bigger than 30mm, i would focus on improvements elsewhere.
might want to check out what Praxis is using on their 35mm spindle. probably the 47mm od bearing, which is why theirs is outboard.

another idea is, going with the 35mm spindle, mount the needle bearing inboard but the left radial bearing outboard. that's the way sweet wings cranks did it in the distant past. with the right bearing inboard, it leaves you the room to have the spider. if right spider width=left outboard cup width, that would be very convenient for symmetry.

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