Over the course of time, many brass instruments will acquire small dents and dings. These changes to the body of the instrument can cause changes in pitch stability, tone and general playability. Then how to removing it? One idea is using magnet. Got a dent in your tuba? Fix it with a magnet. This is done by
inserting a steel ball into the instrument of similar diameter to the thickness of where the dent is located.
A large magnet is then used to control the ball and work it to the dent. Once in place, the ball can be rolled back and forth over the inside of the dent until the dent is worked out. Find more details about magnets seeing link www.aimmagent.com