Sorry for the Threadjack MP, I have move the aviation casting discussion to it's own thread.
MP, I am unfamiliar with the clamp you are making but strong is best.
Last thing you need is something breaking, that can be worse the damaging the work.
on that note you have two options there, 1) operator tuition 2) build in a slip clutch that will limit the permissible torque.
If the clamp is to be used by multiple operator's, the 2 is the one to go for & is very simple to make.
Remember when designing something. The toughest thing on a tool is the 200 pound Gorilla with it in their hands.