Just a little wrench in the works here. I'd be inclined to make them out of a material with a little give to it to acommodate any play or any irregularity in the bore of the wheel. If I'm not mistaken, there's normally a plastic bushing supplied with wheels to make the fit to the arbor. A couple things here- you want the wheel to be as concentric with the shaft as possible, but you don't want the wheel to be forced to follow any and all vibration donated by the motor. The wheel has no give, and if your bushing was solid, there will likely be very high point forces acting on the bore of the wheel. It may never be a problem, but if you can reduce point forces there, then wouldn't the wheel be safer? That's my take on it, and I would recommend using a similar plastic material that the usual bushings are made of. Pvc is my material of choice, partly since I have some in blocks big enough to make these from, and partly because it's easily machinable to a size. Uhmw would be fine, except it doesn't lend itself well to turning to an exact size. I think many other plastics would be better to use than hmw pe or uhmw pe.
By the way, I get my pvc from discarded water and sewer pipe chunks. I just picked up a discarded chunk of 24 inch pressure sewer main (something like that). I previously found a section of 24 inch water main which is identical except that one is rated for potable water. ( I hope so, this is what carries my city's water supply) These pipe materials are a tad over an inch thick, and I normally cut it into manageable segments with my skilsaw, then heat it to formable temperature in the oven. When 'ripe', I flatten it between boards. It's pretty stable after that, and can be worked with woodworking and metalworking tools, though it's a bit hard on hss cutting edges. Read up on the hazards if you've never worked with it before.
[This message has been edited by darryl (edited 12-17-2005).]
I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-