I read a couple of threads on sharpening knives and didn't see any mention of using a belt sander to sharpen knives. I know if you go to most websites about making custom knives they all seem to use a belt sander to shape and sharpen the knives they are fabricating.
Well I bought a used 1 inch by 30 inch belt sander for $18 and an assortment of different grit belts to go with it for $25. It is amazing how fast one can sharpen a knife with a belt sander, less than a minute. You can start with a 220 grit for a knife in bad shape and finish it with a 1200 grit for a polished edge. The thing that slows you down is changing the belts to progressively finer grits, but if you do a whole batch using the same grit and then the next, and so forth that belt changing time becomes a minor part of the whole process. Finish up with a few swipes of a sharpening steel to remove the wire edge.
I can also use it for sharpening lawn mower blades and machetes.