Got a wheel hub that's too big in diameter by 1mm (too tight a fit into the brake disc "hat" - which, fun fact, is not enough to keep the discs from going on but is enough to cause the discs to crack). Mechanic wants to mill out the disc, which would have to be done on all future discs and is not ideal in terms of maintaining the disc's strength. I say mill down the hub. Can it be done? Let me know your opinions.
In most cases, Yes this is perfectly safe. I have turned many hubs to fit into different rotors and some drum hubs to convert to discs.
I've milled hubs smaller in diameter and thinner. Used them in race cars, even. (Well, LeMons cars). All worked fine.
I've never machined one larger in diameter or thicker, though, so I've no idea if that would work. 
I used Toyota hubs on the front of the Locost. I had to turn them for the same reason to fit Miata rotors. Just make sure there's enough material left between the lugstuds and the edge and you should be fine.
Yes turn the hub OD down in a lathe you'll be fine.
Thanks guys. The mechanic's pretty adamant about not doing this for some reason. I'll update this thread if I find a good reason not to.
It's fine - I've turned the OD of ones on my race car more than that and there still plenty of meat where the studs press in. Bear in mind that the hub flange is captured between the head of the stud and the inside of the rotor by 4 or 5 huge, high-tensile fasteners torqued to 85 foot pounds. The shear loads are spread over a very short length, the tension is consistent as it's equal to the clamping force of the nuts.
But do it correctly - take the hubs out, and have someone do it on a lathe, specifically dialed into a 4-jaw if you want the least runout.
Beater car? Angle grinder w/ a depressed-center wheel. Used at an angle so it spins the hub while removing very little material.
Turns out I wasn't asking the right question, took a look at the car yesterday and the part that's too big isn't the face, it's the flange. It has a step-up on the flange (which the original hub doesn't) that makes it too big for the center hole on the disc (which is cracked and splayed out). Don't see why I couldn't machine that down.
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