Yet another vacuum question

[denver]

Hello,
I've been reading a lot of the posts related to this subject, but haven't seen an answer to this, although I could easily have missed it. If I build a multi-zone system, and use a single piece of Trupan for a bleeder, won't it leak internally whenever I have one or more zones turned off? I understand the need for sealing the edges of the bleeder, so doesn't a single large bleeder provide internal leakage paths between zones? Would it be better to use a discrete bleeder for each zone?

Thanks,

Denver

[jhicks]

I tend to agree with you that restricting individual zones would be a benefit but how can one seal in the center/core of the sheet? What we did was sealed around the perimeter of each zone with Allstar Adhesive gasket tape. Not a perfect solution but it does work well to isolate each of them on the top of the plenum and bottom of the bleeder.
Best we could come up with and happy as a clam.

[ed_lang]

Use a 1/8" bit and cut a channel around each zone. Fill with resin or glue. Surface table and enjoy.

[denver]

Thanks, but I suspect I may not have been clear about my original question. Let's say I glue down a 4'x8' piece of MDF, then use the ShopBot supplied plenum pattern for four zones. Than seal that all up (top and sides - bottom already done) with varnish, shellack, epoxy, or whatever. Then surface both sides of a 4'x8' piece of ULMDF, seal up just it's edges. I understand those edges represent a total of 1.5 sqft of leakage (4'+4'+8'+8' * .75" = 1.5 sqft). I also need to use some kind of sealant around the zones between the ULMDF and the plenum. I've seen mention of silicone and gasketing material.

So far so good. Now suppose I want to use just one of those zones. I close three of the valves, and put a piece of 2'x4' material over the zone with the remaining open valve. Doesn't air leak through the 24 sqft of uncovered surface? I understand that there is no direct connection between the zones at the plenum - that's all sealed up. But air can still come down through the entire surface of the ULMDF, travel sideways a bit, then on down into the operating zone. Or doesn't it do that enough to worry about?

Thanks,

Denver

[Brady Watson]

Denver,
Yes, there is some leakage...No, there is not any practical way to eliminate it & in most cases if the edges are sealed, the leakage is negligable. If you find that you are getting excessive leakage between zones, employ the 'trash bag trick' ~ cut up the sides of a trash bag and drape it over the surrounding zones. Keep the dust foot and router away from the plastic...

-B

[woodworkseb]

I've found little Puckers to be the best solution
http://www.oriontechproducts.com/index.html

[bcammack]

[Steven Erber wrote: I've found little Puckers to be the best solution
http://www.oriontechproducts.com/index.html]

Not that you have a vested interest in them or anything...

[woodworkseb]

Great, I see you've visited my web page. I also shared your frustration with vacum hold downs and that is why I formed the company. Our double sided pucks eliminate the FAF (fool around factor) that we all experience in machining small parts from big sheets. With our system one can machine parts 3"x6" while holding fast a 4'x8'sheet. Try that with a regen blower. Most users here are able to produce their own vacum system and pucks, but if you don't have the time or would rather be cutting parts, please consider us for your system or component needs. At the very least I hope our video will give you some ideas for building your own system.