The Kindernay Swap Cage is a removeable hub shell that is a bit delicate for loaded touring. The HD (Heavy Duty) Swap Cage never made it to market.

Kindernay HD Swap Shell

I'd like to make one that's near indestructable. It won't be possible to just copy the original design, and will end up looking something like this:

Flanged pipe I'm assuming any 6000/7000 series aluminium will suffice.

Will the spoke holes need to be beveled? Are grooves and cut-outs simply for weight saving and flair or do they add structural integrity? These are what come to mind, but there must be plenty of pitfalls to watch out for.

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    Maybe a better question for SE Engineering, as most of the audience here mostly combines existing components rather designing them.
    – Rеnаud
    Commented Dec 19, 2023 at 7:45
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    This feels like one of those strong/light/cheap , pick 2 problems. Borrow/buy a high end hub hope/xtr/xx01 and see what they do with finishing and where they leave metal. Definitely ask on engineering.stackexchange.com rather than here. Commented Dec 19, 2023 at 8:48
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    This is a unique opportunity to design it for straight pull spokes which should be stronger and easier to design for (no strange bending torques, no need to think about bevels).
    – Michael
    Commented Dec 19, 2023 at 12:21
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    Counterpoint to asking the question on Engineering SE is unless the right person comes along, the practical elements of the question risk getting lost in frame challenges and base principles. Wheelbuilding related topics are one where non-bike engineers are likely to get way ahead of themselves. Commented Dec 19, 2023 at 16:26
  • I want to purchase your heavy duty hub shell for the Kindernay vii. When you are done completing it let me know and I will buy from you. Commented Jan 31 at 2:01

1 Answer 1


The spoke holes don't absolutely need to be beveled, but it's a good idea. If the head isn't sitting in a bevel, it's essentially going to either wear itself into one or the same effect will need to be done manually by the wheelbuilder before the spoke tension becomes stable and the wheel doesn't go out of true.

On a normal hub with beveled spoke holes, when a wheelbuilder stress relieves the spokes by squeezing them (or using other means) to temporarily overload the tension, one of the things being accomplished is the heads get bedded into the flanges, increasing the contact area ideally to the same point where they'd eventually land with cyclic unloading and loading from riding the bike. If it's a plain hole with a square edge, it's going to take more effort building it to get the same effect and/or take longer in use.

There's another version of the same effect on the J-bend side of each spoke where the spoke needs to cut its groove into the flange. A bevel will hasten that and make it easier to get all the way bedded in during building. It's not strictly necessary but it will add to the probability of success.

A skilled and observant wheelbuilder would see the square edges and know a lot of manual work has to be done to bed the spokes in during building, and then be able to do it. But in the hands of many, it would lead to a wheel that has trouble going out of true.

Generally the very best shells have coined spoke holes. The spoke holes are formed not just with simple cutting to produce the bevel, but with a press or other tool that compresses the material to add strength at the same time as creating the indent.

Many very good shells are made of 6061-T6. It's proven for the application generally, but there are enough unusual things going on with how the Kindernay core interfaces with the shell that actual engineering is probably in order before you can deign have a reasoned answer for a material choice.

The Kindernay core appears to be supported by the shell on the DS with a tapered interface, and it's bolted together on the NDS. That makes it appear like the cutouts in the shell are probably used to help allow the shell to expand slightly as the bolts are tightened. Otherwise, were there none of that effect, I doubt it would be reliable or practical to try and have the length of the shell and core match so precisely that the bolts reach full torque at the exact moment the taper interface makes contact, and also that the contact is then maintained properly under dynamic loads. If so, you'd be on your own for designing a version of the shell without cutouts, and it probably wouldn't work.

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    You're absolutely right. It does have a tapered interface on the interior that I was going to ignore until reading your answer. The simple "pipe" shape won't cut it.
    – Laoshi
    Commented Dec 19, 2023 at 17:15

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