I made an open top box out of 1/4 inch stainless, and sheared a piece of 1/2 stainless that just fit in the box. In each of the four corners I tacked 1" stainless threaded rod and punched appropriate holes in the plate. A two inch coupling welded to the center of the plate accomodates the ram head of a 20 ton press. I leave it under pressure for a while, then run nuts down the rod to maintain pressure for a month or so.
I've tried the setup at home with a 10 ton bottle jack, there is a considerable difference using the larger press.