Universal motors have brushes. As awemawson said, a router speed controller (and a Variac, as well) will work for only these types of motors. They are found in routers, drills, circular saws etc. I don't know what a Biax scraper is. If it's a hand tool, most likely it uses a brushed motor. Brushed motors are usually pretty loud by comparison with others. Check on the side of the motor and see if there are two circular plugs for the brushes.