I buy the cheap die grinders from harbor freight. A guy down the street from me claims to port heads and has 1 expensive die grinder. I usually have 13 cheap grinders in rotation setup with different bits. What I can get done in 15 hours takes him 80 hours. He wastes time changing bits all the time. I basically screwed his world up and no one goes to him any more.

the skinny body cheap die grinders from HF seem to work better and I have both straight and 90* grinders. 90* grinders seem to help with leverage and I can cut more material faster.

need an air dryer close to your work station and I have a ball valve to control air on the tool.

when my 5/3 hp motor went south I bought a real 5hp motor. I also have fans blowing on my compressor when ever I'm hacking

I cut a round sponge and put it in a heavy plastic cup and have enough wd40 in cup to keep the bits cool