David Chamberlain wrote:

MDF works just fine if you finish it. I used spray lacquer on
mine. I drew a vacuum last Saturday and the piece is still
locked down as tight as can be. Based on my experience, you
should incorporate some type of release valve. I will
probably re-design mine so that the vacuum that holds the mdf
to the bench and the vvacuum that holds the workpiece are two
separate lines.

The two-line approach sounds good. I think I might have to build
a few more 'pucks' to play with. I normally use multiple pucks to
hold a workpiece; and for production runs have had to make a mask
of 1/8" hardboard with cutouts for the pucks to keep them from
shifting when the workpiece is removed. A second line would make
that unnecessary - but would double the amount of tubing in the
work area; and would require a second vacuum source.

I started out with UHMWPE and have never had a problem; but know
a number of people who've used MDF and seen poor-to-terrible
performance. I suspect that they just didn't seal the MDF as
thoroughly as you did.

--
Morris Dovey
DeSoto, Iowa USA