I used the Thunder (Thunder) yesterday at 400 spd and 20% power on glass wine bottles for etching. Seemed to work well. And these settings are essentially the same settings that we used during our class a year ago.
I used the same settings on Donner (closest to Metal shop doors?) and managed to crack the bottle. Ended up using 400 spd and 5% power.
I believe Mike (@HankCowdog) yesterday was cutting right through his blue painters tape at 5% power (I forget the spd) while doing a trial run on some stainless tumblers.
Just a heads-up!