Bruno...
Your questions are short and to the point, but the answers can be rather lengthy. I will try to give a really condensed solution.
I'm going to leave the explanations at that so this thread doesn't veer to far from the subject of Josh's razor. If you have more questions, PM me or you can start a new thread. If you have a lot of questions about restoration... just buy my CD...:D
- Rotary tools or Dremel's are only going to be good for restoration work, with the heaviest duty being the removal of some pitting. I suppose you could do a fair amount of metal work with one, but it would take a very long time and not worth the required effort in my book. It will not allow for smooth transition lines, either.
- Heat above 550 degrees is going to take the temper out of the steel you are working on and it will be ruined. If you work on steel and it starts to change color... like yellow, brown, or blue... it's toast
- The trick is to use fresh sanding belts/drums/paper to eliminate some of the heat. The more worn the paper, the more heat is generated.
- Keep the tool you are using from staying in the same spot for too long. I also do not use gloves on treated steel so I can tell when the heat is building too much.