Vacuum Table

[32mmcabinet]

I realize this topic has been covered ad nauseum, but I've read most of the past posts and so far this is my plan:

A) 3/4" Plywood bolted to base. Not surfaced.

B) 3/4" MDF glued down to plywood. Surfaced and grid cut, both done on topside.

C) 3/4" Ultralight Mdf. Skinned, flipped over, glued to high points on grid, surfaced.

Questions:

I'll be using this on a 96"x60" alpha. How do I handle the 60" width? Do I track down 5' x 8' sheet goods, or do I use 4'x8's with an additional 12" rip at each layer. I would guess 5'x8's but would each of the 3 types of materials used come in 5'x8'?

Best type or plywood to use for layer A? I'm guessing this might be swayed by what's available in 5'x8'.

On layer B, do the grid and outside sufaces get sealed?

Whats the best way to glue layer C down to layer B? Glue (a squirt?) at all the points where the two sheets will make contact?

Should I seal the outside edges of layer C?"

Not doubt I've missed something but that's what's coming to mind now.

[beacon14]

For the plywood I am partial to Baltic Birch as it is denser and stiffer than regular plywood. It is available in 5x5 sheets, so you could butt two sheets together. Regular MDF is available up to 5x12. Not so sure about the lighweight MDF. What are the other large table owners using for spoilboards?

Layer B must be sealed against air leakage from below and through the edges. Most people accomplish this by sealing the grid and edges. I prefer to use a barrier layer between the Plywood base and the MDF and then just seal the edges.

Most people use a little glue or silicone to secure the spoilboard layer. Yes it helps to seal the edges of the spoilboard.

Hope this helps.

[knight_toolworks]

I was only going to seal the back and edges of the mdf but then I realized the air can go through the channels to other grids. I find the easiest thing to seal the grid with is thinned down white or yellow glue. it will do it in one coat and dries fast.
yes on gluing to spoilobard then turn on the vacuum and put something on top to seal it so you get max pull. also the yellow or white glue on the edges works well.
I would do 5'x4' sheets with the seam in the middle of the table where there is support and no grid.

[Gary Campbell]

Nat...
If you are looking to keep a stable surface for cutting cabinets spending a couple hours extra at this point will pay big dividends down the road.

Seal both sides and edges of the plywood table board with epoxy prior to mounting it. You will most likely have to splice 2 pieces together and 5' width material as Dave B. says above, spliced over a support should give the best results.

Glue the MDF to the table board with epoxy (I would add thickners similar to various West Systems products) This also seals the back of the plenum.

You can cut the MDF into pieces the sizes of your zones, leaving an 1/8" gap that you can fill with the epoxy and thickner. This will help seal your zones from each other.

Cut your plenum design and seal with epoxy complete. (extra on the outer edges)

When dry surface the plenum. This will leave raw material to allow wood glue to adhere to.

Glue down the Spoil/Bleeder board with wood glue. Glue to all sufaced areas of plenum with ample, but not running all over, amount of glue. To remove, you will have to surface down to plenum, you might as well glue it well.


Yes, seal outer edges of both plenum and spoil/bleeder board.

Remember... if your table warps, the depth of every hole you drill or dado you cut will be off by the amount of the warp. (until next resurface)

Gary

[knight_toolworks]

epoxy would help moisture issues but I would use glue first or you will need more coats of epoxy to seal it.

[32mmcabinet]

David, Steve and Gary, thanks very much for the responses. You've covered a number of things I hadn't even considered.

These forums really are a great asset in terms of learning this whole process. Thanks again for taking the time to post.

[zeykr]

I just put a new spoil board down on my machine. I used a seperate piece of trupan for each zone and sealed the edges with anchorseal. The anchorseal seems to have worked very well for sealing the edge of the spoilboard. I also used All Star Adhesive spoilboard tape between the plenum and spoilboards this time. I seem to have much more holding power this time and no leakage between zones as I had with one single 5x10 mdf spoilboard. I secured each zone spoilboard to plenum with a few nylon bolts in the idea that I can remove one zone spoilboard and replace with a bradyvac type custom spoilboard/mask when needed.

Also have to put in a plug for All-Stars on board gasketing tape. I bought the shopbot starter kit from them and for one shot jobs have been putting a quick outline of the gasket tape down directly on the spoilboard - it really works well!

[32mmcabinet]

A large majority of the time I'll only be using 4'x8' of the 5' x 8' table. How should I layout my zones(4) and deal with the 12" X 8' strip will be exposed most of the time?

[Gary Campbell]

Nat...
I did mine this way...

7696

I will be soon reconfiguring it with the 4 zones in the center as I am adding a dual Z. I will need to "waste" 6" on both sides to allow all 4 tools to reach all of the 96 by 48 area.
Gary

[32mmcabinet]

Gary,

Are 2 of those zones on the same vacuum, or do you use an alternative hold down on the strip to the left?

[Gary Campbell]

Nat..
Each zone has a separate vac motor like this:

7697

I havnt really had to do much with the 5th zone. We have been able to hold everything that has come along with the vacuum and T track.
Gary

[nat_wheatley]

Thanks Gary. Do you use the T-track often?

[Gary Campbell]

Nat...
I would say 15% of the time. Or more than half of the non sheet goods cutting. I cut a lot of plastic & aluminum, and its nice to get the pieces bolted down.
Gary