It seems devices are prevalent, but I was taught the classic razor blade method, and have used it with great success, not mess, no fuss, no smell etc....
Using a NEW single edge razor blade, channels are cut under a flowing stream of water (a kitchen sink will do ....)with the tool at maybe a 45 deg angle or steeper facing towards the cutting hand. It takes a little practice, but with time, it's easy to make straight, sharp edged channels. I cut in at 45 degrees, maybe a 1/4" deep, repeating several times till the channel is close to the correct depth, rotate 180 degrees, and cut the other edge of the same channel. When one direction is done rotate 90 deg. and continue. I usually rotate the razor blade after a couple of channels, and maybe use 2-3 blades over the course of channeling a tool. NEW and SHARP is the key to success, as is a steady stream of cold water. Same technique is used for reopening channels.
We have a couple of channeling mats on the polishing room wall at work, but they havn't been used much..
Bill Marriott btk@ix.netcom.com