Straightening out brass instruments (2013)

There's a great video on repairing a severely damaged tuba, which includes the use of the magnet-ball for straightening the walls of the tubes, as well as disassembling parts of the tuba to gain access to individual parts:

https://www.youtube.com/watch?v=wflildRmcJw

The business of forming pipes with curves typically involves mandrels. A mandrel, in this case, is a solid body that prevents the pipe from deforming in undesirable ways.

https://en.wikipedia.org/wiki/Mandrel

Musical instrument repair is clearly more complex than this—it's a skilled, improvisational profession that would probably welcome this kind of trick. I feel that, outside of Mega City One, those specialists just would not exist, their skills wouldn't be sustainable as a source of employment. That's the economic side of this—it's cool to come up with new techniques for instrument repair, but try being an instrument repairer in a city on the periphery. It's scary that this kind of (fairly mild) specialization is so precarious.

Speaking of hammering from the inside: that's how you make "jumping beans" using a steel ball wrapped in foil:

https://www.youtube.com/watch?v=Y9sl1jLlekk

Made lots of these as a kid.

https://www.youtube.com/watch?v=3BwIOSpD6ro

I am so very disappointed that this article was not about uncoiling the instruments.

This seems very similar to a lot of "paintless" dent repair for automobiles - basically figuring out a way to apply force from the inside to gently smooth out small dents (often with the help of looking at gridlines in the reflection).

I am unconvinced by the 'reverse hammer's method.

Does it rely on eddy currents in the steel ball? Wouldn't copper work much better in that case? Will the ball be large enough for eddy currents to be big enough to have much effect?