Extira Vacuum Table Plenum Board So Dense No Air Leakage??

[rustnrot]

I am planning my vacuum table and am going with the first layer of plywood bolted to the table, then a layer of fiber board of some type with a plenum grid cut into it, then a bleeder board of Trupan on top of that.

I've learned here Extira is VERY heavy and dense. My question is, is Extira so dense that if I cut a grid into it for my plenum board that I could get away with NOT sealing it with epoxy paint?

If I DO need to seal it, is it still a better choice than "standard" MDF to use as a plenum?

[evan]

Extira is heavy and it is dense and it does stink. Pulling air around and over it with your vac system then exhausting it back out into the shop sound like a bad idea to me. I had a job were I had to cut a grid pattern through thirty 1" sheets and I doubt I'll ever cut the stuff again. It was weeks before the shop stopped smelling toxic.

[cip]

I have been using a plenum made from Extira for quite some time and for me it works just great and the smell from the original cutting went away in a day or so. And no I did not seal it and it works just fine.

[rustnrot]

Mike, could you post your table "recipe", i.e. base board bolted to table is ?, how thick Extira? and I assume Trupan bleeder board on top? Did you glue the Extira to the base board? Is the bleeder board glued to the Extira?

What is your vac source? Fein III?

Thanks!

[fleinbach]

Though Extira my work well without any further sealing I personally would use epoxy paint to assure I am getting maximum efficiency.

Let’s say hypothetically unsealed you could obtain 5 inches from a Fein III. But after adding the epoxy paint you are able to draw 5.75 inches. There will always be that one time you are cutting a certain size part and just .75 inches more of holding pressure would have made a difference between a complete part or starting over because it moved and was destroyed.

Since everyone is looking for the maximum holding power for their vacuum to me the extra work is worth it.

[rustnrot]

Frank, 1 coat of two part "garage floor" type epoxy paint was enough, correct? You brushed it on not sprayed also? You did not worry about machining radiused corners as opposed to sharp corners in your plenum board to help prevent possible paint cracking did you?

..I know, it's just a plenum board...

[fleinbach]

Tom,

I used just one coat as it covers fairly well. I used a ball nose bit so all my channels where rounded. it makes it easier to apply the epoxy paint. I put it on heavy enough that it ran down the side walls of the channels making it thicker in the bottom.

Ed Here is a link to my vacuum table layout instructions.

Vacuum Table (http://www.talkshopbot.com/forum/show.cgi?tpc=28&post=42554#POST42554)

Direct link explaining cutting of plenum

Cutting channels (http://www.talkshopbot.com/forum/show.cgi?tpc=28&post=43106#POST43106)

[cip]

Tom, I used a plywood base sealed with polyurathane bolted to the table framing, 3/4 extira counter sunk screwed to the plywood with silicone seal at each vacuum pipe hole, surfaced with the Bot and plenum cut into the extira. Then silicone the spoil board down after surfacing. I have a 15 HP roots pump so I get ample vacuum. ( around 12 to 13 inches )