Plenum Board

[wayne_webb]

Has anyone used Expanded PVC, like 25mm Ex-Cel. I was think the PVC might be good and I wouldn't have to apply polyurethane like you do to MDF.

What about Extira?

If not, does anyone use any other material for your vacuum plenum?
Thanks

[Gary Campbell]

Wayne...
The PVC foam should work well. Cant say about extira, as I havnt used it. There are a few guys using plastic for a plenum on the BT's. I used PVC Solid for mine. Heres how I did it: http://www.shopbottools.com/garysmusings.htm
Gary

[jhicks]

I have also considered Expanded PVC but went with shellaced MDF because I had it in stock. I do believe it would work great though. Just need any stable non pourous stock to make it work. Some like Phenolic sheet as well. Guess its all about cost and personal preferences. Nice photos and set up Gary

[btk]

The PVC works great.
I used a sheet of AZEK.

Brian

[joe]

I would encourage using HDO. It's very flat, slick, non-porus, and very stable. A 3/4" 4'X8' sells for about $60. The dark brown, slick surface is so good looking we've used it for the table tops in the office and display area.

It's a secret, undiscovered, product. Shhhhhh, don't speread the word.

[wayne_webb]

Thanks guys, I went with the Excel Expanded PVC.
If it doesn't work out, we'll try soemthing else.
Thanks all!

[wayne_webb]

I cut the plenum yesterday, but the grooves which run diagonally from corner to corner deflect so that they don't intersect in the dead center of each zone. So if I cut the vacuum holes where the diagonal lines intersect, each hole will be closer to one end, instead of dead center of each zone. Is this the way it's supposed to be?

5984

[scottbot]

Wayne,
I drew my own plenum in AutoCAD so I'm not sure what the ShopBot plenum file is like.
But mine too are not dead centre. The reason they are that way is so they holes will miss the metal support brackets under the table.

Scott

[wayne_webb]

Thanks Scott,
It looks like I can drill the holes dead center and still miss the brackets. Do the holes have to be located at those intersections for optimum vacumm performance?

[scottbot]

One would think so but I really don't know.

[beacon14]

The last table I built had some of the holes well off center and I am told it works just fine. A lot will depend on how much leakage you are getting from through cuts etc. With no leakage it should not make any difference, the more leakage you have the more you might notice that the areas near the holes have better holding power than the areas farthest from the holes. That will be the case even if the holes are centered, but it might be more noticeable the more off-center your holes are.

[Gary Campbell]

Wayne...
I have 3/8" wide by 5/16" deep grooves in my plenum. I have tested and do have reduced vacuum when measure on top of the spoilboard more than 20" from the Vac port.

If you do cut the holes in the center, you can always add a few more diagonal cuts. Even if you are not comfortable doing this now, you will be in a short time.
Gary

[wayne_webb]

I used a 1/2'' wide roundnose bit and routed the grooves .3" deep. I think I will cut the holes in the center and maybe join a couple more grooves to that. The PVC was about $135 so too expensive to cut another one.
Thanks everyone.