Plastic or HDPE vac plenum?

[EricSchimel]

I know I have my MDF plenum sealed up pretty good, but I'm depending on a thin layer of glue/shellac. That's why I'm thinking that PVC/HDPE would make a good plenum because it's way more airtight. Do I know it will work better? No, that's why I'm asking here!

[tomkk]

I have zero experience with PVC/HDPE. How does it compare to phenolic as far as weight, price, machinability?

[mark_stief]

Just throwing this out there. Why glue it down if you would just take wood dowels and pin it on all 4 corners so it couldn't slide when sliding sheet goods on the vacuum would hold both pieces down. I'm looking for a piece of plastic for my table and that was my theory if I find one for the right price

[tomkk]

Mark

I was thinking along the same lines. I guess the only disadvantage would be if you were running something without vacuum. But WOW it sure would make spoilboard replacement a breeze!

[tomkk]

Mark

Interstate plastics list 3/4 HDPE at $283.57
3/4 PVC at $384.48
3/4 PHENOLIC At 520.53 all 4 x 8

[mark_stief]

I'm not sure 3/4 would stay level I was thinking 1" or even 1.25" it's the shipping that kills the deal kinda Why couldn't you scuff the edges and use some caulk I have some Solar Seal caulk that will stick to any thing it hits

[tomkk]

I think if you seal the bottom of 3/4 ply then bolt to frame then glue your 3/4 phenolic and machine your plenum it will stay flat forever. I don't know if you have any experience with Phenolic ?
This stuff is like steel plate! I'm not an expert by any means, and hope others chime in with their opinions. Eventually I will just go for it and be the Guinea pig. I salvaged several sheets from a local cabinet shop. So I have nothing to lose but time and effort. I can't help but think that this will also prove Eric's thoughts on improved vacuum!

[EricSchimel]

So I'm back revisiting this... I did some bench tests gluing HDPE to plywood... It doesn't grab very well as expected... I know HDPE can curl if you take a bunch of material off of one side so. If I mill a plenum into it I think it will want to curl up and pull of the base layer....

So, I'm thinking either PVC, or maybe just sticking with my MDF plenum and sealing it again now that I'll have it open again.

[jerry_stanek]

I just looked at this again and I had the old MDF plenum and now the Sintra the Sintra is a lot nicer and I think I do get more holding power

[bobmoore]

I made my router bed with 3/4 hardwood apple ply for a base, layed on a 1/8 mdf as the 2nd layer and milled that flat with the bot. the 3rd layer is 12 millimeter corian with the vacuum grid machined in, then 3/4 inch mdf spoilboard to top it off. It works real nice with 8 -10 horse becker pumps. Bob