Interesting Tool Project!!!
 

Nice!

http://www.autobody101.com/articles/...shing%20Hammer

Damn that is cool. If I ever get to playing with sheet I will have to knock one of those off. Manual hammering is a pain in the bicep!!!

I would be inclined to want to use a regulator and a foot control with a bypass valve that you could turn on and off by hand. With the hand valve you could crank it open and set the regulator to the desired impact.
My Foot gets tired stepping on a controller very long.