general lapidary saw info

I've never understood how cutting a grinding wheel would expose diamonds on the blade. If cutting hard stones like agates dulled the blade to begin with, cutting a hard grinding wheel doesnt seem like the way to sharpen it.

I've had much better luck with swaging the blade. Basically bang the edge of a course file along the rim of the blade. Misshapes the softer steel, exposing new diamonds.

I regularly make cuts into a hard aluminum oxide grinding wheel to sharpen blades on my tile saw or large MK brick saw.  It absolutely works to expose fresh diamonds.  Never had to do so with my lapidary slab saw since the extremely slow cut rate does not seem to wear diamonds any faster than it wears the metal matrix that holds the diamonds.  

Agates are hard, but not very hard compared to diamonds.  It takes an extremely long time to actually wear down diamonds by cutting agates.  Rather than the diamonds actually wearing down, they more often chip or fracture until there is almost no diamond exposed on the cutting face of the blade.  When this happens, the blade cut poorly since the steel matrix does not grind through rock very well if at all.  This happens most often with manual feed saws (trim saws, tile saws, etc) since pushing the rock into the blade with too much pressure will fracture the exposed diamonds long before they are actually worn down from cutting.  Agates are hard but not very abrasive, so they do a poor job of wearing down the steel matrix that holds the diamonds.  So trying to cut agates with a "dull" diamond blade will do little to expose more diamonds.  

Cutting a grinding wheel (AO seems to work better than SiC wheels) exposes diamonds because the grinding wheel is much more abrasive than an agate.  A grinding wheel is designed to wear down metal, so a few cuts through a grinding wheel will wear down the steel matrix but will not fracture or wear the diamonds in the blade to any significant extent.  So you'll end up with exposed diamonds because you have worn down the matrix.  

Good slab saw blades seem to have a hard matrix since the slow feed speed will do almost nothing to the exposed diamonds in the blade.  I have heard of people using the same slab saw blade for many years with little wear.  If you were to put that same blade on a tile saw and manually ram rocks through it, you might have to dress the blade every few cuts.