I have a Whitney 5 ton kickpress and need to punch 3/8" holes in 0.040 thick aluminum that is preformed into an 8" deep channel about 8" wide (holes in the bottom). I was hoping the gibs of the press (which are well adjusted and tight) would provide the alignment needed. But the flex of the press frame seems to allow the bottom platform to move down slightly (about 0.005") relative to the ram and in moving to move down slightly more on the front than the back. This causes the pedestal that fits into the upside down channel to spring forward about 0.010" - much more than the clearance of the die. I have very little experience with this sort of thing. I am thinking a die set is needed but it would need to be a fairly large one.

Currently drilling with a step drill but it produces a large, difficult to remove burr on the back side and is slow.