What, nobody remembers hitting the stem on their bike?
That tool is exceedingly easy to make. and easy to extract. When it's time to remove it, you just unscrew the t handle half way, and hit it with a mallet.
You would measure depth to get the mandrel under the dent. The wedge bridges the dent. It would be very difficult to over expand it, as the force you can apply decreases as the wedge slowly mates with the tube.
The best dent raisers are Horn repairmen. Their livelyhood is removing dents from curved tubing.
