Plastic or HDPE vac plenum?

[EricSchimel]

That's kinda the vibe I've been seeing Brady, that plastics just don't stay flat. As someone who cuts HDPE all the time I can definitely attest to it curling a bit.

In all honesty my MDF plenum has worked great and remained for the most part very flat. I've coated it several times with Shellac, do you think I can go over the top with this epoxy coat, or should I just Shellac it again?

[Brady Watson]

Eric,
Anything that seals the MDF essentially plasticizes it & keeps moisture and suction in...If you're happy with beetle bellies, go for it.

-B

[EricSchimel]

I'm happy with 'em, I just didn't want to pass up an opportunity to put something better on when I have the spoilboard off again

[wwaldner]

Thanks guys
I think I will go with conventional wisdom, especially since this is my first go at a vacuum bed setup.

Brady, you mention coating the MDF with epoxy. Here is what I am planning on doing.
1. Sheet of MDO bolted to frame. Not planning on sealing or coating MDO.
2. Epoxy MDF sheet to MDO and cut plenum. Not sure if epoxy is necessary as this step as the MDO under MDF would seal it. Thoughts?
3. Cut plenum grid and ??
1. (shellac/poly/epoxy) the plenum to seal it. Brady, is this step where the epoxy sealing comes in?
2. I have some epoxy bar top coating left over from another project. Wonder if that wouldn't do the trick in sealing things up.
4. surface another piece of MDF for bleeder and glue that plenum

Thanks for the help

[Brady Watson]

MDO, being Med Density Overlay (with phenolic paper), doesn't need to be sealed on the faces. The edges however wouldn't mind being coated. Scratch the face with the sander a little to help with glueing/bonding.

Yes, the MDF grid and edges should be sealed with epoxy. 2 coats is good, after you flatten the entire thing because clamp pressure will cause low spots. When done sealing, kiss the top flat again before glueing down the bleeder. With so many sharp edges, epoxy is bound to puddle under surface tension on the 2nd coat and create some high spots on the grid squares...or just from drips.

I have no experience using bar top epoxy for sealing so do what you think is best. Shellac or thin laminating epoxy is best because you'll get the MDF to wick up the first coat before it kicks.

-B

[wwaldner]

Thanks for the advice guys. There is a lot of info out there and it helps to get some specific questions answered.

[wwaldner]

Eric,
Do you have a VCarve file for your vac plenum with the 8 zones? Would you mind sharing?

[EricSchimel]

I'm more than happy to share mine, however mine was designed for my "V8 Vacuum"

https://3dwarehouse.sketchup.com/mod...-Vacuum-System

Mine's got the holes in different places than normal to make it all work. At the end of the day mine's just an 8 zone vacuum table. Each zone is 24" x 24" and I've got a 1" grid in each zone. Pretty simple to duplicate. I'm more than happy to share my files, but I think you'll spend as much time hacking mine as you would drawing a grid from scratch...

[wwaldner]

Do you know the spacing you used for your grid, between zones and outside perimeter?

[EricSchimel]

Do you have SketchUp? (even the free version on the web) you can look at the model and measure the grid, it's right there.

The grid in the model I did as an "on line" cut with a .25" bit.