Scarf board Issues

[ccwerks]

I have recently moved the machine to a much more moist environment. Im finding it difficult at best to keep MDF from soaking up and warping. I tried to silicone it down to the plenum and it does fine for a day or so then it lets go. I then went to using a spline in the boarders of the plenum. Im finding that to be equally as disappointing. can any one suggest a more stable material to use.

[bleeth]

I'm in Florida and have ended up with the following system:

In addition to gluing the plenum to the sub base I add some screws in the channels at the corners before I put the spoilboard down. I also seal the plenum chambers, top, and edges with shellac (two coats)
I glue the spoilboard with Titebond 2. I put a glue line all the way around the outside and along the high dividers between zones. I have eight zones with the vac hole in the center of each zone.
I also put a dab of glue on each raised bit around the vac holes so in essence I have 8 glue rectangles with dabs near the center of each rectangle. I flip on the vac after gluing the spoilboard until I get a stack of sheet stock on top to act as weigh-down (6-8 sheets of melamine or ply or mdf) and leave it overnight. If I have to screw something down to the spoilboard in the corners I'm careful to ensure the screws are not hitting the chambers in the plenum, as once the spoilboard starts getting thinner I pretty much have to screw into the plenum.

[ccwerks]

Dave thanks Ill give that a run..... just out of curiosity does the depth of the channels in the plenum make a difference? Im sitting at .250 V bit cut. I have surfaced it down a few times.

[bleeth]

I cut my plenum channels with a 1/2" straight bit 3/8 deep and the grid has 1" between channels with a bit more at zone borders to make it easier to glue and like yours over time it gets shaved a bit when putting down all new spoilboard (if the old one is clean at 1/4" or less I leave it there and just glue the next on top). My Vac is a 7.5 regen. Never used a v-bit as I think having some volume there helps. Maybe some other guys used v-channels and can chime in.

[jerry_stanek]

On mine I cut the mdf into 4 2x4 pieces and ran a groove in the plenum that I install 6 mm sintra strips. This not only helps with the warping but isolates the zones