Spoilboard problem this time

[meatbal80]

I just finished truing up the router and surfaced my spoilboard. I have a setup like Gary with the directly mounted vacumes split into 5 zones (the regular 4 - 2x4 zones with the lower left split into 2 zones). All of my zones have their own spoilboard. When i removed the skin from the uldf i used i was running the vacume hold down which worked great now i see that all of my spoil boards are cupping bad. I cannot get the vacume to even hold down the spoilboard with out something on top to seal it or push down. Did i do something wrong? I was planning on installing gasket around the perimeter but have not had a chance but i dont really want the hastle of having silicone to clean off every time i switch out the spoilboards. Any advice? If someone would have some time to help me out over the phone that would be much appreciated as this is just one of many hurdles i am trying to clear. I took the class at shop bot headquarters but still have many questions left.

Thank you
Joel J

[ken_rychlik]

Most folks either glue or screw them down.

Mine is Glued with construction adheasive. apply glue, turn on vac and thow plastic over it so it will pull down hard. Let it run with the vac and plastic for a few hours.

[Gary Campbell]

Joel....
Like you I tried to work with a loose fitting spoilboard and like those before me (thanks Brady) I finally went to a fully glued down spoilboard and have had very good results since. Most people think that MDF is a moisture stable product and it is not! MDF with a veneer on 2 faces and edges sealed is an inexpensive way to get a flat panel for a while, but not over the long run.

Once you skin out MDF it is like a sponge, drawing moisture out of the air. As you run the vacs, the center will dry out and then your spoilboard section will turn into a potato chip.

BTW, you did nothing wrong.

[meatbal80]

Ok before i glue the spoil board down how do i know that my plenum is sealed? I had a friend come over and spray about 2 gallons of m.l. cambell sealer and lacquer on it. Gary i found your vac setup the most appealing when i went to design mine what numbers do you get? Once i am sure about the plenum being sealed should i glue around the perimiter or on top of all of the squares and the perimiter?

I really appreciate all of the help, you might think of me as green but trust me i was red today with frustration. If any of you find yourself in Phoenix look me up and i will take you out for a beer.

Thanks again
Joel

[Gary Campbell]

Joel...
I have changed my plenum 3 times so far and I havent decided what I am going to do with my next machine. I am hoping to do an aluminum plenum and std mdf for a bleeder and then add a wasteboard.

If you are asking about vac numbers, with the setup and motors shown in my early column, I got just under 7.5 inHg with a full sheet on the table. I have changed motors and now get just under 10 inHg.

I glue solid around the edges of each zone and every other block. Mine are on 4" centers.

[knight_toolworks]

the easiest way to seal it is to thin down some yellow glue and brush it on. one coat is usually all you need.

[ken_rychlik]

I think when I get done abusing this plenum, I will try a sheet of exteria next time. It is exterior rated mdf. I have used it for some outside signs and I have a piece thrown in the yard just to see if it would swell up.

It's been a few months and the weather has not affected it.

It's about 3 times the price of mdf, but much cheaper than aluminum. lol

The only trouble you will have if your plenum is sealed very well, is getting the glue to stick to it. You are not bonding to the board anymore, but to the layers of lacquer.

I think gary used gorilla glue, but I have had good luck with lacquer based construction adheasive.

Kenneth

[meatbal80]

There is definatly a good layer of lacquer on the plenum and i think that some silicone will hold the spoilboard down well. I am just worried that i dont have the plenum sealed as well as i should. is there some way to check. I dont want to silicone down the spoilboard only to remove it shortly after to get at the plenum.

[dlcw]

Joel,

I applied two coats of shellac to my plenum and it's sealed really well. No leaks. I opted for mounting the vacuum pumps directly to my plenum (thank you Ed Lang) and at 2500' altitude, I was pulling at most 6.5 inHg with the spoil board just laying on top of the plenum. I finally bit the bullet and used silicon to seal my spoil board to plenum and now I'm at 7.5 inHg in all four zones. Before gluing down, each zone had a different vacuum amount.

I use a piece of 1/2" Trupan for spoil board for each zone and apply heat activated glued melamine edge banding around all four sides of each board. I spread adhesive all around the edges and then on every fourth little tower (see photo) in the plenum. The vacuum motors are attached directly to the plenum (see photo). I also put 1/4" plastic tubing into each plenum and then to a vacuum gauge to get my readings.

I'm glad I did to the glue down. It has helped a LOT.

[ken_rychlik]

Joel,

Silicone will not hold it.

[dlcw]

Kenneth,

Silicon has been holding mine for about 2 months and over 100 hours of vacuum on time.

Have you had bad luck with silicon? In your experience, what might be a better adhesive?

[ken_rychlik]

Don

Silicone and water based construction adheasive both turned loose on mine.

I am using the lacquer based construction aheasive with better luck.

I guess what you seal the plenum with makes a difference on what will stick to it.

Kenneth