Q-Factor as narrow as practical with and without a lathe :-)

Ok the narrow BB requested has been made and I used a spare pair of cranks to set the alignment. :)
A pair of tube sections will go with it (for the end-user to finish off) these go over the JST stubs and are cut/filed to size to fill the gap between the inner face of the cranks and the inner bearing race. This is intended to stop the bearings "walking" out of the unit.
Personally, I would use a "bearing glue" to fix the bearings in, but the unit may go in a carbon/resin frame and you can't use heat to unglue again.
Housing width 42.5mm.
Overall width 90mm.

image.png
 
Trickytrike said:
Sorry I am a little confused, was that for a unicycle ?
do you mean the hardened steel would have lost temper after welding, but you didn't lose yours filing for ... hats off
Click to expand...

Yes, it was for a unicycle.
I made the axle from a chuck of steel rod. I hand filed it square, then drilled and tapped the bold holes at the ends.

I had tried welding a square bike axle together once, but it failed due to being higher carbon steel.

Brad
 
Radical Brad said:
Yes, it was for a unicycle.
I made the axle from a chuck of steel rod. I hand filed it square, then drilled and tapped the bold holes at the ends.

I had tried welding a square bike axle together once, but it failed due to being higher carbon steel.

Brad
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Why wouldn't a higher carbon steel weld together?
I hope that my melting the base stuff of both halves and stirring them with the tig-torch flame is enough to re-introduce the 2 halves.
It is only after that was happening that I added filler material.
 
DannyC said:
Why wouldn't a higher carbon steel weld together?
I hope that my melting the base stuff of both halves and stirring them with the tig-torch flame is enough to re-introduce the 2 halves.
It is only after that was happening that I added filler material.
Click to expand...
The heat effected zone will become brittle unless allowed to cool extremely slowly. Even then... kinda iffy.
I tried a pre and post heat on steel like this with some success, but decided it just wasn't worth the risk.

Here is what I did (ultra high tech) to test the bb axles I tried welding after they cooled...

Put them firmly in a large vice with boards between to protect the races, then hit the extended end as hard as I could with a 4 3 foot long bit of 4x4 lumber.

Of 4 of them which I pre and post cooled as well as chanfered for proper 100% weld, all but one shatered at the weld.

I figured I may be subject to a leg injury if I was really pushing hard on the cranks and one sis that, so I chickened out and started using the lower carbon "drill rod" to make my own. Did a narrow one like yours and two mega wides for choppers, all good.

Maybe my basic buzz bix was just too crude for such technical welding!

Brad
 
Radical Brad said:
The heat effected zone will become brittle unless allowed to cool extremely slowly. Even then... kinda iffy.
I tried a pre and post heat on steel like this with some success, but decided it just wasn't worth the risk.

Here is what I did (ultra high tech) to test the bb axles I tried welding after they cooled...

Put them firmly in a large vice with boards between to protect the races, then hit the extended end as hard as I could with a 4 3 foot long bit of 4x4 lumber.

Of 4 of them which I pre and post cooled as well as chanfered for proper 100% weld, all but one shatered at the weld.

I figured I may be subject to a leg injury if I was really pushing hard on the cranks and one sis that, so I chickened out and started using the lower carbon "drill rod" to make my own. Did a narrow one like yours and two mega wides for choppers, all good.

Maybe my basic buzz bix was just too crude for such technical welding!

Brad
Click to expand...
Well you have me worried now. :( I don't want to injure anyone.
 
Thinking about this a little (not a lot) it seems to me that a "shock-load" like hitting something with a large mass might not be the best test.
In a recumbent application the rider is not "standing astride" the opposing pedals he is pushing/pulling the pedals against the forces of inertia/uphill climbs and the bike should be moving before something gives way?
As the recumbent riders output something on the range of 350 .. 500 watts of power let's up that to 750w.
Now 1 HP is 550ft/lbs so if I fix1 crank in a vise and have the other at 90° and extend the crank to 24" and can hang 280# on it without it snapping then maybe it's unlikely to snap in real usage.

What do you guys think?
 
That would work - I like the "twist to failure" mode of testing.
If / when it does fail, at least you'll sleep well, knowing you erred on the side of safety - And you can always just weld up another one ;)
 
Cracks propagate. They creep over time. So your testing should have push and pull cycles of around 80 cadence frequency for several hours and then repeated for? I don't know. So this becomes a destructive test.
Safety factors could be as high as x5. I think my firm used about x3 at the low end. So we'd test lifting capacities, for example, with 3x to 5x times the weight of the lift requirement.
Did you read the welding link that I put up?

All in all, an engineering firm would not make the short BB the way you have. It would be machined as one piece without any welds.
But they are up against possible corporate convictions if things go pants.
Just saying.
 
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Dale Rider said:
Cracks propagate. They creep over time. So your testing should have push and pull cycles of around 80 cadence frequency for several hours and then repeated for? I don't know. So this becomes a destructive test.
Safety factors could be as high as x5. I think my firm used about x3 at the low end. So we'd test lifting capacities, for example, with 3x to 5x times the weight of the lift requirement.
Did you read the welding link that I put up?

All in all, an engineering firm would not make the short BB the way you have. It would be machined as one piece without any welds.
But they are up against possible corporate convictions if things go pants.
Just saying.
Click to expand...
Yup, I get that completely. I have destruction tested it and it failed far more easily than I had anticipated. But I was whaling on it with my 200# on a 2 & 1/2 foot extension tube. :)
 
OK, I can think of 2 ways to resolve this. Use raw steel stock like Brad did, or don't weld it put a keyway in to join the 2 halves and put it in a cut-down BB-shell with screwed-in end-caps. :)
 
DannyC said:
put a keyway in
Click to expand...
Hmm - Next weakest link theory
Maybe, if you used a high strength key, and machine to a close tolerance fit.

What about re-visiting the weld idea, only instead of a butt joint, mill a half-lap joint, and weld around the entire seam.
But you need a mill, either for a keyway, or my half lapped idea - Maybe time to tool up ;)
Those BB axles have the look of being forged, to my eye, rather than just machined - Probably what makes them strong.
 
undertoad said:
Hmm - Next weakest link theory
Maybe, if you used a high strength key, and machine to a close tolerance fit.

What about re-visiting the weld idea, only instead of a butt joint, mill a half-lap joint, and weld around the entire seam.
But you need a mill, either for a keyway, or my half lapped idea - Maybe time to tool up ;)
Those BB axles have the look of being forged, to my eye, rather than just machined - Probably what makes them strong.
Click to expand...
Yes, I think they are hot forged and "stamped" out as blanks and then have the bearing mounts machined and the ends drilled and tapped.
 
Funny, I rode many 12ft+ tallbikes around town without a helmet, raced my Maurader downhill at 90+ km/hr with one rear brake but was afraid to weld a BB together! I just keep imagining a scenario where I am in the lower front chainring just power cranking up a hill and it lets go, turns sidways and embeds the large chainring right into the artery in my leg like a huge oriental throwing star!

I am odd that way though, and would still ride a 12 foot bike around town or attempt 100km/hr downhill on a home built bent!

Oh, and I also tried welding car axles for my many giant robot projects. On some occasions with very carefull weld filling and pre/post heat, they would hold to the 2-4hp torque I put on them with electric motors. On some occasions they would snap and splinter like glass. I just don't like welding anything with high carbon content.

Brad
 
Plug welding is notoriously hard to perfect. Lots of competent welders have had failed plugs on joining bits of car together. It's much easier to weld the edges of the tube and should create a much bigger welded area too. The tube may need to be shorter to keep weld off the bearing seat.

If using a mig and plugging you absolutely have to strike the arc on the inner or bottom steel. If you light it up on the edge of the plug hole the puddle gets minimal penetration to the bottom bit. I guess tig has a similar need to attach to the lower bit first. The smaller the hole diameter the harder it is.
 
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Popshot said:
Plug welding is notoriously hard to perfect. Lots of competent welders have had failed plugs on joining bits of car together. It's much easier to weld the edges of the tube and should create a much bigger welded area too. The tube may need to be shorter to keep weld off the bearing seat.

If using a mig and plugging you absolutely have to strike the arc on the inner or bottom steel. If you light it up on the edge of the plug hole the puddle gets minimal penetration to the bottom bit. I guess tig has a similar need to attach to the lower bit first. The smaller the hole diameter the harder it is.
Click to expand...
The hole was 8mm and I did have the inner/bottom surface glowing bright orange and I thought I had "stirred it around" with the tig flame before introducing any filler. Oh well, I shall go another route.
 
DannyC said:
Yup, I get that completely. I have destruction tested it and it failed far more easily than I had anticipated. But I was whaling on it with my 200# on a 2 & 1/2 foot extension tube. :)
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Crikey I go away for 2 days racing and this think all falls apart ;)

So I can't see any description or pictures of how/where it failed ? so we are just guessing what any remedy/alternate build method maybe ?

Paul
 
stormbird said:
Crikey I go away for 2 days racing and this think all falls apart ;)

So I can't see any description or pictures of how/where it failed ? so we are just guessing what any remedy/alternate build method maybe ?

Paul
Click to expand...
We don't wash our dirty linen in public, only our successes. ;)
The "plug" failed to bond with the axle, there was minimal/no decent penetration. A fine line of bright weld was visible adhering to the ends of the axle halves.
 
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