table thickness and construction ideas

[banderson]

Good morning. Working on assembling my PRS and wanted some opinions on the composition of the table (router with no vacuum). Manual says to go with the plywood on the bottom and then a couple of sheets of MDF. Is this the best thing to do in your experienced opinion?

[dana_swift]

Mdf is ok, but for a solid spoilboard I like plywood better. It doesnt swell as much when the humidity changes.

[Brady Watson]

ShopBot recommends 3/4" cabinet grade plywood as the support board and a layer of MDF on top as your spoilboard.

I prefer MDO plywood as the support board with Medex moisture resistant MDF glued to it as the spoilboard. The combo of these two are super stable.

-B

[tuck]

I have double 3/4" MDF, always have, with no particular problems. I have an old wooden table (48 x 96) and I fasten down the MDF with counter-sunk lag screws into the 2x4 supports, about 24 screws total. If it swells and moves, I can't see it, nor does it really effect the kind of work I do.

I through-cut a lot of 1/2" Ultraboard with an 1/8" bit. I broke a lot of bits on the MDF, then thought of fastening down a 3/4" sheet of cheap foam insulation board with counter-sunk pocket screws. Viola! No more broken bits! And the foam is easy and cheap to replace after it starts getting to be really chewed up,....about $14.00.

[blackhawk]

Bret - For my opinion, I would go with MDO for the support board, as Brady suggested. Then 1 layer of MDF on top of that.

I bought my Shopbot used and it had plywood and 2 layers of MDF. That much thickness limited me on some projects that had thick work pieces. With 2 layers of MDF, you lose 3/4" of stroke with your router. Over the past 3 years, I have finally surfaced my table enough to get rid of that entire 2nd layer.

Try it with 1 layer of MDF to start out with, you can always add the 2nd layer if you decide that you need it. It is much harder to surface off a layer.

[dlcw]

Bret

For my PRSAlpha 96x60 I went with two layers of 3/4" Baltic Birch plywood for the plenum and started with a 3/4" piece of ultra-light MDF for the spoil board. The MDF is edge banded with plastic laminate to reduce vacuum leaks.

I mounted the first sheet of Baltic Birch using the bolts through legs. The second layer of Baltic Birch was glued to the first layer. I then surfaced the Baltic Birch to get a nice flat working surface. I then cut my 7-zone plenum. Next operation was to surface one side of the MDF, turn it over and use silicone adhesive to mount it to the plenum. I used the vacuum system to hold the MDF down until the silicone set up. I then surfaced the working side of the MDF and have been very happy with my setup.

When the original sheet of MDF gets to 1/4" thick, I will edge band and glue new pieces of 3/4" MDF over it (the glue only goes around the edges and a few locations in the field). I'm ready to go back to work.

[Charlie Iliff]

ShopBot recommends 3/4" cabinet grade plywood as the support board and a layer of MDF on top as your spoilboard.

I prefer MDO plywood as the support board with Medex moisture resistant MDF glued to it as the spoilboard. The combo of these two are super stable.

-B

Brady:
For my 4 x 8 Buddy table, I was worried about weight, so went with 5/8 MDO and 3/8 moisture-resistant MDF. We glued it with epoxy, and were amazed when a corner separated in about a foot. We'd sanded both surfaces with 80 grit. Best guess is that the surface peeled off the MDO, but we glued it back together without checking carefully.
I've seen that you have recommended both yellow glue and Gorilla Glue. We've not tried Gorilla, but have had problems with TiteBond II on MDF.
Any secrets about surface prep and glue selection?
Charlie Iliff

[joe]

I seldom see anyone, on this forum, using HDO. It's several times more moisture resistant than MDO and very flat. This material isn't available in most retail lumber yards. It's often used to make concrete forms and stands up under lots of moisture. I get it at wholesale lumber yards.

As a sacrifice board I like Extira. It's moisture resistant, almost water proof. Keep in mind it's only the surface of MDEDX which is water resistant. The interior material is much like particle board and will swell with moisture. Odd as it may seem, Trupan swells less than Medex.

I hope it's not true but I've heard that Trupan is due to be discontinued. I love that stuff. Over the past year I've been using it for letters. Once sealed up it will last outside. It's so easy on my back and my router bits last much longer.

Joe Crumley
www.normansignco.com