I have never noticed that putting a bevel on the edge of pads has any effect on squeal. I don't think the edge of the pad is the spot that squeal originates from or what perpetuates it. Deglazing the face of the pads can help sometimes. Just scuff the friction material on the pad lightly with a little sandpaper, and make sure there are NO contaminants in the pads at all. With full metal pads you can heat the pads (held in a vise or pliers) carefully with a propane torch in short bursts until they stop smoking. That burns any voliatiles (oil, etc) off. This also melts of ignites organic pads, so know what you are cooking. You may also be able to buy pads with a different compound which will reduce squeal. The stock compound in Magura Louise brakes are excellent- basically squeal free. The aftermarket pads for Louises by Kool-Stop are a lot noisier.