I used to get all mine from a local industrial supply, guy would stop by on his route and just drop them off. Price was good but the quality was so-so. I've been going through McMaster lately for most of my abrasives and buying in quantity to get good pricing. The Zirconia belts definitely last longer, obviously cost more but I believe they're worth it. 50-60 grit is a good compromise between material removal and longevity.
I've always used belt disk combo machines. Use the disk for material removal so run a 60 grit disk, belt for fine tuning things usually 100-120 grit. Usually order from Grainger or McMaster-Carr and get the zirconia stuff.
I order Norton zirconium oxide belts for my little bench sander at my local airgas. My belts are 4x36 and cost right around $10 a piece. I have a buddy who is a ferrier and uses a Jet multi tool on his truck while shoeing horses, his uses a 2x36 belt and he tried the nortons on my suggestion, and did not like them as much as the zirconium oxide 3M belts that are out there. Say's the 3M's last considerably longer, but I personaly don't have first hand experiences w/ the 3M's.
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