SB Bed

[twelchPTM]

When my Shopbot was set up we were told to get a sheet of MDO for the bottom layer of the bed, my local lumber yard could only get it in pre-primed.
Do to concern that the glue would not adhere properly we used a sheet of 3/4 a/c plywood. Well that has comeback to bite me since the plywood has and continues to warp my table top is constantly out of wack. It also seems to have caused a nasty fissure on 2 of the edges of my vacuum grid. As I prepare to rip it all off and start over I am wondering what other materials people have used for the bottom layer and how that worked out for them?

[dlcw]

I used 2 layers of 3/4" baltic birch. I've had no problems at all with my table. But take this lightly as I live in a part of the country that has very low dewpoints (humidity) year around. If I'd gotten my Shopbot when I lived in Ohio, I probably would have used particle board for my table. Something that didn't respond, quite as much, to large humidity swings year around.

[shilala]

I'm in Ohio, about 30 miles from the Lake, and I have to replace my table. The shop is the garage, it's not climate-controlled.
My BT48 came with a 1" particle board "starter table" on it, and it's curling up like it wants to be round. It's truly awful, but Shopbot's intent was not to supply a table that would carry me through the ages, just to give me something to play on. It's served me well. :)
I put a 24"x48" piece of 3/4 Baltic Birch Plywood in the center and surfaced it, that's what I work on. That's fine for the moment, but I'm ready to outgrow that any minute.

Any suggestions you guys can make for my situation, that'd be great. I was thinking a couple sheets of particle board based on what Don said. Maybe a couple layers of 13/16" glued and screwed?
My surface area is 54x48, I don't even know if I can find a 10' sheet around here. If not, I'll do what it takes.

[twelchPTM]

I am in philly, my shop has a giant chiller/heater that makes it super hot in the winter and stupid cold in the summer. I try not to run it but I share the shop with a few other guys. MDO is not readily available but can be easily ordered, the Lowes and HD's around here carry oak ply, maple/birch ply and arraco(def spelled wrong but the stuff is ****). I don't really want to replace the whole table but the plywood is warped so bad I can see the bend in the suppurt channels underneath.

[ken_rychlik]

The main thing I found is to seal it from both sides. If you put a plenum or another board on top of it and leave the bottom unfinished, it will be trouble.

I used prefinished birch ply on a few machines and have Baltic birch on this one. I think the baltic is a little more stable. You won't find the 5x5 baltic sheets at a hd though.

[twelchPTM]

my table is only 4x8 so finding a sheet of whatever I end up using won't be to hard. I've been reading up on the topic all day and there seems to be 3 main products used baltic birch, mdf, and mdo. however there are a alot of different opinions on what to seal and how to seal it. there in lies another obstacle.. if the board isn't flat when i seal it won't it stay not-flat?

[shilala]

Now I'm starting to think I may just make a table for the 6' powerstick sitting in the corner. I'm in a pretty tight space and don't really want to use a bigger table, but I want to make a couple long, skinny wall hangings that I can't do on the 4' table.
I'll just make the table 4' wide rather than 4'6" that's on there now. That'll keep the edges closer to the rollers and should help keep it straight.
I hadn't thought of sealing the table, that's a great idea. Even shellac would help get the double-backed tape off and help stop destroying the top.

[twelchPTM]

well i think i got this any high quality hardwood plywood, properly preped and sealed should provide a stable base for my table. I have some maple cabinet grade in stock I think that will do....

[dhunt]

We are lucky in that our PRT-96 has spent the last 11 years in an air conditioned room!

Here on a tropical island, humidity can get nasty
so our aircon situation has not (yet?) affected the original sheet of ordinary 3/4 ply we used as the base
back in Feb/March 2001.

When I go in this morning, I have to take a look..
now the subject of warpage has been brought up.


Recently we've been cutting quite a bit of UPVC-foam-board
so my thoughts run to the possibility of using a sheet of 20mm. foam-board
rather than wood of any kind?
-or would this stuff compress, over time?

[lcolburn]

Thomas, I'm in Philly too, and have been running a Bot for the last couple years here in town. My current setup is 3/4" Baltic birch as a base for a MDF vacuum system. That said, my Bot is only a 4'x4', so getting a big enough piece of Baltic was easy.

I've been able to get MDO at much more reasonable prices through N.Glantz (sign-making supply) here in Philly. Mr. Robert's Lumber, just across the Walt Whitman bridge, can special order nearly everything, but their prices on MDO were higher than Glantz. Just my two cents.

[twelchPTM]

Thank you, I never heard of Glantz but I'll be checking them out...