Shopbot deck.

[gundog]

I am not putting in vacuum at this time so I am just putting down 2 sheets of plywood and one layer of MDF. The directions say to bolt down the first sheet then countersink the second sheet with screws but say nothing about attaching the MDF.

I bought some liquid nails to glue down the MDF. Is that sound like the way to go on the third sheet? I also don't understand why I need to mill both side of the MDF. If I glue it down why not just glue it down and mill it flat and call it good?
Mike

[gundog]

It seems to me I should screw the second sheet from the bottom of the machine or I will never be able to take it apart later to add a vacum to it.

[knight_toolworks]

you want to surface both sides to make it stable. one surface off and it will warp and it may just pull away after you glue it.

[myxpykalix]

By milling both sides you take off that top layer of paper and it makes the mdf more pourous and your vacumn better.
Also a good tip that Ed L. taught me. After you are all done attaching your mdf take some silicone caulk and apply liberally to the edges all around the plywood and mdf layers. That will seal the sides from leakage.
I used yellow glue to attach my mdf. I wouldn't use liquid nails. I don't know for sure but i would think the liquid nails would not allow air to pass thru it.

[myxpykalix]

oops! I just reread the post and i missed the word "not" ! "I am NOT putting in vacuum" which makes most of what i wrote irrelevent.

You may want to consider using nylon toilet tank nuts and bolts. If you run into them no ruined bit and if you have to remove that sheet to make a vacumn table you should be able to cut the tops of the bolts off with a good 1/2" bit and the rest of it will fall down to the floor.

[ed_lang]

My suggestion would be to bolt the first sheet to the steel cross members and glue the second sheet to the first and then glue the MDF to the second sheet. Mechanical fasteners will cause you trouble by both hitting them as well as causing the sheet to pucker and or lift at those screw location.

glue and glue with lots of heavy objects laying on top for pressure. Not not think clamps around the edge will do a good job.

As you surface the MDF to remove the cuts, you can glue another sheet of MDF on to replace it. Later if you want to add vacuum, and I expect you will, you can surface the MDF off and cut the second sheet of ply for the zones and then glue a sheet of Trupan on top of that.

Good luck and be sure to ask questions if you have further ones.

[gundog]

Thanks for the advice I think I will go with Ed's suggestion. Do you think liquid nails is the best glue for this?
Mike

[beacon14]

If you plan to glue the layers together (which I also recommend) I suggest vacuum-gluing instead of weights and/or clamps. Read up on the Brady-vac II method, machine a simple grid in what will be the bottom of the layer to be glued down, rout a hole in the base layer for a shop-vac hose (or two), spread the glue, lay the sheet on with the grid down, turn on the shop-vac(s) and cover the whole thing with a sheet of melamine or plastic to contain the vacuum. You will get MUCH more uniform pressure than you could realistically achieve with clamps, weights or screws. Anytime you are gluing large flat surfaces together (think veneer) the amount of pressure is not as important as having even, uniform pressure across the entire sheet.

If you don't believe me try it on a small mock-up to see for yourself. I'd use PVA glue (yellow or white woodworking glue) or polyurethane adhesive (Gorilla glue or similar) instead of panel adhesive for an even, uniform glue line. You will never get panel adhesive to form a thin even glue line no matter how much pressure you put on it.

[ed_lang]

Mike,

David is right in my opinion, that using vacuum would be a LOT better. My suggestion is the next best thing IF you are NOT going to have vacuum available.

I would suggest that you DO NOT use liquid nails or any other thick bonding agent. Use PVA in my opinion. I like TightBond II.

Let us know how it all works out for you.

[gundog]

I do have 2 shop vacs they are not feins just a craftsman & a rigid. Will they work to vac down this glue process?

I have bolted down one 3/4" cabinet grade plywood sheet and I have another one to go on top of that and then a 5/8" piece of MDF. I am ready to glue down that second sheet now. I will take the 2 tubes of liquid nails back and look for some titebond.

Do I route this grid by hand or with the Shopbot? Where can I find this info on the Brady Vac II method?
Mike

[Gary Campbell]

Michael...
Use which of your vacs seem to pull the hardest. Keep an eye out for overheating.

Look Here: http://www.shopbottools.com/BradysTricks.htm

You bought the ShopBot to be able to route designs like this grid and not have to do it by hand. Go for it! Good Luck!
Gary

[beacon14]

The shopvacs should work just fine - if you use Titebond you should only have to run them for an hour or so each time. But I would hesitate to leave them unattended during that hour just in case.