Elkins and gathert, unless mine is different, the Lee Bench Plate system actually has a hole pre-drilled in the wood pieces and the mounting plate and the presses just for the purpose of a "safety" - something like a screw or a screwdriver that goes through the press/tool, wood piece, and bench and keeps the press from slipping off.
Anyway, it's good to know I'm not doing anything wrong, because your presses get loose too.
Elkins you mentioned the "way it is shaped" - meaning the whole bench plate set-up with the wood mounting pieces. Just occurred to me - what if the trapezoid (yes, I remember that one thing from geometry) had the top or small end pointing out, towards the edge of the bench, instead of inward? The press loosens up because of the motion/force of resizing and belling the case mouth.
If we mounted a press the other way - top of press towards the long side of the wood piece - and of course reversed the bench plate so that its long side was on the inside, away from the edge of the bench, wouldn't it pretty much put a stop to the problem we're talking about?
Lee is kind enough to supply 3/4 wood pieces - but they're pre-drilled, so we'd have to drill new holes to mount the press to them. And then of course another set of holes to mount the bench plate in the reverse direction. I don't really want to perforate my nice butcher block bench surface that much - wish I knew about the loosening issue before I mounted this to begin with.
Is there any other idea you guys have about ending this issue - the bench plate system is a great idea, seems kind of stupid to be always checking if the press is secure (as I do).