How do you suggest that I mount the rotor for mountain bike brakes onto a plain steel axle that is 1/2 in diameter?
i suggest finding an old mountian bike front hub that accepts a disk rotor, take out the axle and bearings, bore it out to 1/2 inch, then slide it over the axle. now drill thru the hub AND axle perpendicular to axis of rotation, install a bolt that connects them together (so they rotate as one unit) only thing i would be worried about is the strength of the axle where you drill the hole, best make it as small as possible yet big enough that the bolt wont snap when you hit the brakes.
Axles don't turn, so there is no point in mounting a disc rotor on an axle. Disc rotors are mounted on the body of the hub shell, as Bikeworks explained
Rotors don't mount to the axle, they mount to the hub body using one of 2 methods- either they are bolted on with 6 hardened steel bolts or they are fitted to a special spline then held on with a lock ring. You could, in theory, take a rotor to a machine shop and have them make an adapter so you could thread the adapter onto the axle followed up with a locknut and attach the rotor to the adapter. I could probably make this up in a couple of hours but a person unfamiliar would likely take much longer. I have a question now. how are you going to mount the caliper if you get the rotor mounted?
