I read the threads in July regarding axles moving inside the hub, and in particular the question of whether this problem had emerged on other brands, such as the Qu-ax. This week I ordered and received a Qu-ax 20" muni with splined hub. It looks awesome and feels awesome except that I can feel the axle slipping inside the hub. I have of course made sure that the cranks are really snug on the axle and also applied anti-seize as would be appropriate.
Also the axle inside my right pedal was loose and when I opened it I found that one of the bolts had fallen off and it was not possible to tighten it. The threads on the axle must be damaged.
Anyhow, Fler Bollar i Luften in Sweden have been very helpful and I’m returning the faulty parts today.
I built a 24" MUni with Qu-AX hub and Halo SAS rim 3-4 months ago and had it through some good testing so far, just not enough to verify it in my eyes. So far no problems whatsoever, and the workmanship is first order.
That’s the way the DM spline hub is made. The steel flanges are welded to the steel axle.
The problem with pressing a steel axle in an aluminum hub is that the manufacturing tolerances are very tight. They have to hold the manufacturing to very tight tolerances. I’m not sure exactly how tight the tolerances have to be, but it’s in the range of just a few thousandths of an inch. If they machine the hole in the aluminum hub just a little bit too big then the press fit is not going to be tight enough. If the keyway gets machined just a little too wide then the keys will have room to move in the keyway. Getting a tight press fit requires precision machining and careful quality control.
I’m also not sure what type of aluminum alloy they’re using for the hub body. If it’s one of the softer aluminum alloys then that could be a problem. Maybe if they went with one of the harder (and more expensive) aluminum alloys, like something in the 7000 series like maybe 7075, then maybe the hubs would hold up better. Maybe.
But the real problem is the need to keep very tight tolerances on the machining for the press fit and keyway design to work. This is a problem for the Profile design, KH design, Qu-ax design, Onza design, or any other hub that relies on press fitting a steel axle in an aluminum hub body.
I don’t know why one of the companies doesn’t do a hub with steel flanges welded to the axle. DM has one, but the only way to get the DM hub is to buy a DMATU or DM Vortex.
One reason may be that they’re all bicycle companies. They’ve already got the aluminum hub bodies for bike hubs. They figure why not use the same hub body for the unicycle hub. It is an easier solution for them.
One other thing that might be influencing their thinking is that aluminum flanges are better on the spokes than steel flanges. Aluminum is softer and the aluminum will deform around the shoulder of the spoke and support the spoke better. With steel flanges the steel spoke holes can cut into the shoulder of the spoke because the steel has no give. With steel flanges you’re more likely to have a spoke break at the shoulder. Also with steel flanges you cannot tension the spokes as tightly because the spoke shoulders don’t have as much support. So with aluminum flanges you can build up the wheel tighter and have a stronger wheel.