Question about plenums and vacuum

[mrps]

First off I have a Standard Buddy 32 and I’ve had it about 3 weeks. I’ve figured out I don’t like screwing everything down or using tabs, so I’m going to make a vacuum hold down system. I’ve figured out my plenum size, cut files and how to hook it up to a vacuum motor by using a second sheet under the plenum with a vacuum channel.

Now before I make this whole thing I have a few questions.

I thought of this instead of using T track and I’m wondering if any one has tried this before? If so, how does/did it work?

Will this be a problem for maintaining a vacuum seal?

Gary, what do you use for the perimeter gasket? Do I need one?

Or should I just use T track?


8405

Drill holes all the way through the plenum on every third square. Counter sink the bottom of each hole to accommodate a t-nut. Glue the plenum down to the middle sheet and then to the table top. This will allow hold down all the way across the plenum and easy squaring of your work using dowels placed in acrylic or wood blocks. Now I know you shouldn’t need hold down spots with vacuum, but if you drill matching holes in a secondary spoil board you have hold down across you entire spoil board if I don't use vacuum.

[myxpykalix]

Keep in mind you will lose vacumn thru the sides of your mdf so take some silicone caulk and smear it along all your edges to seal them. That keeps your air pressure flow on your flat sides and not on the edges.

[rcnewcomb]

quote:what do you use for the perimeter gasket?
I use material from All Star Adhesives (http://www.allstaradhesives.com/). They have been great to deal with.

[erik_f]

I used HDPE for my plenum. Its expensive, but very stable. Also, since you are using the BT you can get a chuck for not too much. My 2x4' by 3/4" cost me $100. Then there are no worries about leaks or sealing it...you will also want to use a bleader made of Ultra Low Density Fiber board (ULDF). I didn't use any perimeter gasket since the bleader board sits on top of the actual plenum and acts as the spoil board as well.

[Gary Campbell]

Mike...
The bolt holes should work well for attaching the different jigs/corners etc. that you mention. I would use them OR t track, but not both.

If the plenum is made from a porous material it is most likely that you will get leakage thru the bolt holes to the bottom.

I used a 1/4" wide by 1/16" thick adhesive backed gasket from AllStar. I have eliminated this feature on my new table as it allows us to get vacuum closer to the edges. We now glue our spoilboard to the plenum.

Having the option to attach corner blocks or jigs is a great feature, as you may not want to hear the vacuum, some materials do not hold well, and it is always nice to have a way to index a part to flop it over or recut itself or another just like it.

I dont know much about the buddy, but Brady did a great job researching what works and has an article that puts a vac table on the Buddy. http://www.talkshopbot.com/forum/messages/27/27659.html Make sure you look it over before you build. In any case do some backwards research and read his posts concerning vacuum. In most of the areas that we varied from his postings, we ended up coming back to them for one reason or another. (mostly performance
)
Gary