Tried a vacuum fixture on thin sheet, it buckled like paper

I figured a cheap vacuum table would hold some .040 aluminum for engraving in my shop outside Tulsa. Pushed the pressure up to 20 inHg and the part warped in the middle, ruined 3 blanks before I backed it off. Guess I should have used a backing plate or lower vacuum, but the chatter got worse then. Has anyone else fought this with thin stock, or is there a trick I'm missing?

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the_charlie10d ago

Did you ever try dropping to like 10 inHg and just taking lighter passes? I used to crank vacuum thinking more hold equals better cut, but thin stock taught me the opposite real fast.