Lumber for the table

[crash5050]

I have done a lot of reading on the forums, but I still want to ask this question so I don't screw something up.

Main table 3/4 inch baltic birch
Plenum, 3/4 inch mdf (how do I attach this to the birch effectivley)?
spoilboard, 3/4 inch mdf.
Run the surfacing routine on the spoilboard.

Attaching the spoilboard to the Plenum, I am going to use tight bond glue, it seems to ooze into the mdf and create a good seal.

If I am wrong here, please let me know

David

P.S. Gary, I may need to call you about plumbing this thing. I just bought 4 Lighthouse motors.

[Brady Watson]

Here (http://www.talkshopbot.com/forum/showthread.php?t=14892) and here (http://www.talkshopbot.com/forum/showthread.php?t=14742) and here (http://www.talkshopbot.com/forum/search.php?searchid=1014004) (SB Search)....

Just about every question you are going to have regarding table layup & vacuum configurations has already been answered. If you can't find the results via the Forum Search, use Google to search the Forum. (E.G. - type "vacuum plumbing site:www.talkshopbot.com/forum" in the Google search box)

;)

-B

[garyc]

David...
My methods and materials as follows:

1st layer, Table board: 3/4 MDO or Shop Birch as 2nd choice. Bolted to to table frame

2nd layer, Plenum: 3/4 industrial particle board or MDF as 2nd choice. Fully glued with Titebond and screwed if needed to keep flat. Remove screws next day, cut plenum and ports, seal with lacquer or poly, surface when dry

3rd layer, Spoilboard/Bleeder: Trupan or ULDF as second choice. Surfaced .010 on one side, flipped, surfaced on the other. Test to ensure air flow prior to gluing!!. (if other than Trupan) Glue with Titebond to raised sections of plenum. I usually surface the spoilboard next day after moisture from glue has equalized.

Save the cutting file for the plenum. When the spoiboard has been surfaced down to about 1/4", run the plenum file .030 deep with a v bit to mark the areas NOT to glue. Surface a new 3/4 Trupan and glue it to the top of the existing 1/4" spoilboard. Seal all the edges with Edgeband, Titebond, Tape, Caulk or Poly

[zandeauto]

My methods and materials as follows:

2nd layer, Plenum: 3/4 industrial particle board or MDF as 2nd choice. Fully glued with Titebond and screwed if needed to keep flat. Remove screws next day, cut plenum and ports, seal with lacquer or poly, surface when dry

So I have a question about sealing my plenum. I used 3/4" particle board as recommended above. I purchased shellac as I thought is what I needed but I'm not sure if it working out very well. Reading too many posts i guess and thought that was what i needed. I have applied 2 coats and it all soaks in to the material and dries to a flat dry finish. I was hoping for a nice glossy finish to know it is sealed well. So to my question: will the shellac seal the particle board well enough even though it isn't a hard glossy surface?

Oh and why surface the table after applying the sealer instead of before you cut your plenum pattern? Doesn't this just remove what you just put on?

[Red F]

I'm new to shopbots but I would assume that you need to surface the plenum so that glue will stick to it. Glue doesn't stick to finish very well.

Feel free to correct me if I'm wrong.

[bleeth]

I have been using a similar method with slight variation for years. I prefer regular density MDF to industrial particle board and I flatten the top and cut the plenum chambers prior to sealing. I do use shellac. I then screw down the bleeder, turn the vac on, shave it, and then flip and glue it down with titebond. Run the vac for a couple hours and/or weight it down with a stack of stuff until dry, seal edges, and then surface the top.
Never was sure why Gary preferred PB over MDF. There are so many different grades of PB out there and some of it is really porous, which you don't need in your plenum at all. I can attest that his system worked very well also.
You should be fine with 2 coats of shellac, but if it bothers you go ahead and put on another-it doesn't take long!!

[twelchPTM]

you really don't need a super bond between the spoilboard and the plenum, just good enough to hold it flat and in place, then the vacuum hold it as well.
as far as sealing your plenum - Gloss + Glue = Bad, glossy surfaces don't hold glue very well as they tend to be very smooth and provide little for the glue to hold on to.

[twelchPTM]

another thought, to seal or not to seal, it really depends on your vaccum. We bought the big honkin vaccum from shopbot along with our machine and I don't worry about sealing the plenum or the table edges, in fact if I did I would have to worry about sucking the ceiling down on to the table