Even with a c clamp or other clamping or magnet, the easiest and cheapest is still hit it with a 4 or 41/2" flap or grinder disk to remove the rust. The other thing you have to consider is that each piece of steel you add will need a mating part cleaned for good contact. Its just a fact of life. Clean you clamp and the steel.
Been there, probably broke it, doing that!
I am not a lawyer, and never played one on TV!
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