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I've spent hours reading everything I can on plenum/vac/tables. With all your experience, what is the best adhesive to use between my birch and the plenum and what is the best sealer and application method for the plenum? (yellow glue, poly, shellac, tight bond, etc.) Should I surface the birch plywood before attaching the plenum? And wouldn't it be more adaptable to use gasket in the cut lines instead of leaving a 1.5 inch ridge between your zones? Then you could change your zones as needed.
I'm assuming you are using MDF for the plenum. Just about anything will work at this stage as long as it is spread over it all evenly. I have used yellow glue and contact cement with fine results. My first two plenums were glued to the base with TB and the latest is down with Contact cement. No problems with any of them. For sealer I've been using shellac for years. I just brush in a couple coats before I set the spoil board.
For your last question I don't quite get it. I have 8 zones with 1" or so between them and have no issues with appreciable loss of vacuum when not using all zones.
Thank you, Sir.
Yes, i have a couple of sheets of Trupan. I picked up a gallon of Tite Bond and a gallon of shellac after church this morning. I just ordered the 4 Lighthouse LH 7123 motors this weekend, so won't have the vac available when we cut the plenum. RE the last question: Two days ago I saw a guy's plenum on a Multi-Cam. His "waffle" had no separate zones; it was all one big waffle. But, he used a white gasket material to outline his "zones" where ever it made sense for what he was cutting. (He bought it used 3 months ago and it came that way, so he wasn't much help.) I just wondered if maybe this was more versatile than the standard "cut each zone with the wood being the divider." You have 8 zones....I don't remember your table size. I've thought about that - then use one motor per 2 zones. If your plenum is 4 X 8...mind sharing your plenum FP? I would feel better NOT destroying my first $40 sheet of Trupan!
After securing plenum boards to the cross arms surface it flat and smooth. Cut the plenum channels and the vacuum holes. I leave a 1.25" ridge between zones.
Sand everything smooth. Important to get everything smooth to reduce/eliminate obstructions to air flow in the plenum.
Seal with 4 coats of shellac (spray can works great if you don't have a Cricket sprayer).
Attach your vacuum system. Test run to make sure it all works.
I cut my Trupan to be the same size as my zones and then edge band each piece with plastic laminate. Provides a good edge sealer.
Between plenum and spoil boards I use silicon chalk. A thin bead along the edges and a few in the middle to keep the spoil board flat. Engage the vacuum motors and let it sit for about an hour. Spoil board now securely held to the plenum.
Surface spoil board and your in business.
Start to finish about 1.5 days. Most is to let the shellac and chalk dry thoroughly.
You should surface both sides of your spoil board one side then glue that side down after the glue sets up surface the other.