PVC Plenum for 4x8 vac table?

[knight_toolworks]

How do you stick the pdf down to such materials?

[evan]

Since I don't have strong enough vacuum (just a diy two motor "black box") I glue the MDF along edges and across the bed every 24". When it gets surfaced down to about 5/16" I glue new MDF on top. A couple times a year I pull it all off and remove the residue from the 1.25" x 60" x 120" Richlite Plenum with the 2.5" surfacing bit, and start over. IF I had an industrial vacuum I wouldn't have to glue it down, just hold it in place along with the material being cut.

[knight_toolworks]

Since I don't have strong enough vacuum (just a diy two motor "black box") I glue the MDF along edges and across the bed every 24". When it gets surfaced down to about 5/16" I glue new MDF on top. A couple times a year I pull it all off and remove the residue from the 1.25" x 60" x 120" Richlite Plenum with the 2.5" surfacing bit, and start over. IF I had an industrial vacuum I wouldn't have to glue it down, just hold it in place along with the material being cut.

yes but what did you glue it down with? not much sticks.

[JuniorLee]

Mark how did you seal the connection between the top and the PVC (I assume) pipe?
Jr

[jerry_stanek]

I surface the PVC then use tite bond III It holds to my Trupan. In fact I just replaced the Trupan this week and had trouble getting the drips that were in the groves from last time off the PVC

[evan]

knight-toolworks-

With clear Gorrilla glue... used liquid nails once but decided it was over kill.

[sbd1]

I've used a sealed MDF plenum under a sacrificial spoilboard for ~8 years, no problems. And while I don't have experience with plastic plenums, I agree with Eval that HDPE has HUGE thermal movement. I've used sheets of it for other projects.

As for gluing to a non-porous material, I'd highly recommend a melamine glue (ie: Wilsonart, RooGlue, etc...).

[sbd1]

I just came across this comment by coryatjohn in this thread that seemed particularly well related to temperature concerns.

"Another interesting thing to consider is if you have your pumps under your table, and they generate a significant heat load, they can actually change the precision of your table significantly, especially if the heating is uneven. Say you have your pumps at one end of the table and they get to 140f. That means there could be a 70 degree gradient over the length of your table. The change in dimensions of your table would be enough to be measurable."