Veneering

Ryan emailed me regarding my comment that the gasket tape doesn't stick well to polyurethane and wondered if sticking it to the platen might be better.

A platen mounted gasket might stick better, but it seems like it would be easy to damage the gasket even if you weren't in the habit of sliding things in and out of the press. Mounting the gasket to a rabbet that runs around the the perimeter of the platen might work.

Despite the poor adhesion, the gasket on my first press has stayed stuck and functional. Joe recommends acetone or xylene to prep polyurethane for seaming so I gave acetone a try on my last press. I used a strip of laminate to protect the wood and a folded bit of acetone dampened (not wet) Scotch-Brite to clean a strip wide enough for the gasket. While adhesion is better, its still not as good as mounting the gasket to lacquered wood.
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Peter brought this up earlier [link] and I thought I'd expand on my reply.

Flat membranes are easy to seal, but you cannot veneer things more than a few inches thick. To get maximum capacity the membrane should be as loose as possible. Let the sides of the membrane curve in from the corners as much as you can. Even though you cannot gain much on the diagonal corner-to-corner dimension, the extra material everywhere else really helps. The membrane-seal-platen design also adds capacity. With the membrane on top of the frame, lost capacity equals frame thickness because the membrane will have to travel that extra distance (if there is enough material to do so) when vacuum pulls it tight to the frame. I tried a reversible frame on my 4x8 press thinking it would increase capacity, but raising the membrane up like that had a serious negative effect on capacity.

Box membranes are a good choice for veneering thicker items but they are hard to make and seal. I don't think either of my attempts would would work well with an auto cycling setup. I'm also not sure if my glued box joint [link] is any better than my folded one [link]. I wonder how the commercial ones are made.
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