Hi Paul,
If you follow the advice of Anthony Mount (and me also) buy your belts from J&L.their “Zirconium” range are particularly good. Although the joint is taped , I have not broken one yet.
If you have an adventurous turn of mind you could also cut sections of proper belt sander belts, there is one which has the same length belt but it is about 3″ wide, which of course will make several for a powerfile.
If you have belts that has a glued joint, which has failed, Super glue will join them back together, but do try to keep everything in line!
I have shortened belts before (for a linisher) by removing the abrasive to create a scarfed joint and used Super glue to stick the ends together, so it can be done!
If anyone is interested in why I was being such a cheapskate, I was given some belts and i was not going to let them go to waste.
It must be remembered that how you use your powerfile, does have an effect on belt life.
christephens