A glass artist is never lacking in scrap bits of glass, and I always tell my students that they can turn their scrap into frit using a coffee grinder! Well, I figured I should try it out and see if it really works!!
Here are the necessary tools: coffee grinder (retired, never use for coffee again!), mask and eye protection
First cut up your scrap (rod or flat glass) into manageable size little chunks that will fit into the coffee grinder politely. Then put it in there, pulse away, and voila!
IMPORTANT: after you grind it up, wait before opening the grinder, and if possible hold the grinder under an exhaust fan when you open it up. There will be a good deal of powdered glass dust created and its important not to breath it in.