[Rick TYler]

Daniel, I feel your pain. This has been discussed here early in the design season. My suggestion is not to panic, but be prepared if the inspector doesn't listen to reason (which is that the appropriate rule is "don't damage the balls" not "don't build your mechanism with this material"). If the inspectors complain, your backup solution is to turn the belts inside-out. They will almost certainly still work fine, but the inspector won't freak out about the abrasive surface.

If you are using really fine sandpaper (like 220 or finer) it is probably less abrasive than a lot of surfaces other teams are using. Try reasoning with the inspector. If you are using 32 grit -- I suppose you are on your own.

We did a lot of testing with well-worn 220-grit belts and they worked great and didn't damage the balls. It's just prejudice. Our final robot conveyor system replaced the sanding belts with timing belts (which weighed more and didn't work as well, IMO). Good luck.