I have to make an 1/8 inch cut on a 6" strip of granite with an angle grinder and diamond blade. I am not worried about dust for such a small cut, but I do not want to break or chip the granite.
Is there a benefit to getting the blade wet?
I have used a diamond blade in an angle grinder to make detailed cuts in ceramic tile without getting the blade wet. Everything worked fine.
Whether you use water or not is entirely dependent on the blade, not the material (unless you are cutting something soluble in water). Some binders used in diamond blades and bits take heat better than others, and the trade off is how the cut works (aggressive material removal, smooth finish, ability to cut heterogeneous materials, etc.)
Do not use water with a dry cut blade, and don't run a wet blade dry - follow the recommendations from the manufacturer. AKA, RTFM.
If you do it incorrectly, your blade will either not cut, wear out too fast, burn the material or the blade sintering, or just blow apart entirely.
And remember, lower speed and less pressure make for a slower, but safer, more precise cut with far less dust and wear on the tool and the blade.
Wet or dry depends on the blade more than the material. I slab a lot of rock. I use an oil for lubricant. Blades last forever. If you are using a sintered blade, the sparks are from the diamond bond being too soft for the job. As it wear down, the steel blade sandwiched in between the bond material makes contact and sparks. Smart Cut diamond blades website gives you a hell of a lot of info. Nothing wrong with sparks if you don't mind chewing through blades. Continuous rim blades should be used wet. Slotted blades can be used dry but are a harsher cut.
You Do NOT need cooling water to cut granite. I have seen videos of 3 foot thick slabs being cut into 2 inch thick slabs for counter tops. Part of the high cost of granite is the cutting process.
A smooth finish adds more cost. A rough finish done by blasting the surface with plasma torches also adds cost. None of these processes involved cooling water.
Still, the cutting speed needs to be controlled so the cutter plate and shaft do not overheat. Compared to most materials, granite is cut slowly. If water is used, it is to clear out the sludge that builds up when cutting large pieces for counter tops or leveling plates.
