I bought the 120, 240 and 400-grit flap wheels from Widgetsupply.com. I tried one out today, and I'm getting some chattering. Should I be using more pressure, less pressure, more speed, less?

I'm using a Dremel with the flex-shaft, and the speed is on two, I think.

Any miscellaneous tips for using these things? I'm restoring a big W&B half-hollow.

Josh