Stressed Skin Table

[mnrite@yahoo.com]

Has anyone built a wood table using a 61-1/2" x 120" x 4" Stressed Skin Panel(like hollow core door)for the main table? The center 4'x8' could be a vacuum zone. I think it would be very rigid and stable. If I used LVL for the sides how far should they extend above the panel?

Thanks
Mike

[davidallen]

my current table has 2X4's on edge, sandwiched between 2 sheets of plywood. is that similar?

[mnrite@yahoo.com]

David
Yes, That's similar, I was thinking of using MDF top and bottom, I can get that in a 5'x10' sheet making the rigid table top large enough to mount the X rails directly to it. The core pcs would be MDF also because I think it would stay straighter. This way the hole thing would be one rigid unit. What do you think?

Thanks
Mike

[fleinbach]

Mike
I see no reason this wouldn't work but instead of standard 2X4's I would use LVL 2X4's also. My old PRT table was made with 1 7/8" X 9 1/4" side rails and 2X4 LVL cross members. I put a 1" MDF main board on top and a 3/4" MDF spoil board.

[bill.young]

Mike,

I use a 4'x8'x6" stressed skin panel for my table top, but it sits on a wooden table. I'd thought about just getting a bigger panel and mounting something to the long edges to mount the rails to but never tried it out.

The concept was that it would sit on stands of some sort when I was using it and be stable enough to raise to the ceiling on cables when I needed more room. I wasn't that concerned that it would twist because the rails would stay parallel to the edges of the panels, but it seemed like there were a couple of details that had the potential to be catastrophic...like working under something that heavy...so I lost my nerve before giving it a try. I feel like it would work OK if you didn't try to make it "upwardly mobile".

Even if you don't decide to attach the rails to it a stressed skin panel makes a great top. Mine was made by a local company with a foam core (a good choice for light weight and strength), and the skins were glued and vacuum bagged on. If you want a top that stays flat and can modify the table design so that it can handle the extra thickness it's a great choice.

Bill

[gerald_d]

I don't see an obvious problem except that you might want to put some dust "scuppers" (drain-holes) under the rails.

Keep an eye on the suction power (WG) of your intended vacuum pump to prevent your skins from taking on a "hungry horse" look (rib ripples).

[mnrite@yahoo.com]

IF I build this way, How far above the top of the panel is the top of the LVL, and do I hold 61-1/2 inside or 64-1/2 outside between the LVL's?

Thanks
Mike

[fleinbach]

You can get a set of plans with dimensions from here http://www.shopbottools.com/manuals.htm

[gerald_d]

Mike, hold the 64.5" across the outside. The top of the LVL's should be around 5" above the top - this will give you the same as the steel table guys with a 6" beam minus 1" for the support board.

Added after Frank's most recent post above:...
The wood table plans gives the main x-beams only 4" above the cross-bearers - adding a 1" support board to that will only leave 3" from the top of the table surface to under the x-rails. This is very much lower than the steel plans. Am I reading these drawings correctly?

[fleinbach]

Gerald
I believe you are correct. It's been nearly two years since I built my wood table. I sold it with my old PRT96 last year so I can't look at it for referance. They call for standard 2X4 attached to 2X8 side. so since a 2X4 is 3 1/2" actual and a 2X8 is 7 1/4" actual you wind up with 3 3/4" of space before you attach your X rail. I believe the X rail is 2" angle and I remember adding large nuts as spacers increasing the space by another 1" So you have a total of 6 3/4" before adding your spoil board. I used a 9 1/4" LVL and increased the space by 2 more inches.

[mnrite@yahoo.com]

So I am looking for around 6" from the top of spoilboard to top of LVL(bottom of X rail).

Thanks
Mike

[wooddr]

Mike,

I just built my table out of the 9-1/2" LVL's, we call them microlams out here in Idaho. I made my joists out of 3/4" laminated Baltic birch to have joist of 1-1/2" x 5-1/2". When they shipped my Shopbot they thought I was building a metal table so they didn't ship me the kit to attach the rails for a wooden table. It was a blessing for me because I used a 2x3x10' chunk of L metal to attach the long rails with. That way I was able to mount the rails like the steel tables and not use the 7/8" nuts for spacers. I bolted the L metal into the side of the microlams every 10" or so and left about 1-1/4" from the top of the microlam to the bottom of the L metal.This so far has made a pretty sturdy table for me. I know it isn't as strong as the metal ones, but I only have about $300 in it too.

I can e-mail you details if you want.

Dirk Dunham

[alabama_davo]

Hey guys, I have to add my 35 cents worth. Like Dirk I used LVL (laminated veneer lumber...or really thick plywood) however, I used 11 7/8 x 2 for the rails and 8 x 2 for the cross joists on 12" centers. I also used mortise and tenon joinery with polyurethane glue. Eack joist has 2 6" lag bolts through the sides etc. This table is much stiffer than any of the 20 or so ones that I've seen including steel. A tip if you think you want one, the LVL lumber is designed for LONG spans and typically large building centers will end up with many "cut-offs" from 6-8 feet and if you ask the right person, you can buy them for pennies on the dollar. I have $225.00 in the LVL and about 50 bucks in hardware. After the table is assembled and level, secure it to the floor and the first program I ran was the "surfacing" program to true all the joists...Then I added 2 layers of 1" mdf and it hasen't moved of twisted or anything for 17 months (in Alabama of all places). If you need help building this Tim Allen wannabe table, just ask.

P.S. I wish I would have designed in a place for the Indexer I just bought...

Have fun.

Dave Patterson
205-222-6866

[alabama_davo]

Hello again,
I almost forgot about telling y'all about not needing the stressed skin... The table deck on my table is so flat it's silly and by surfacing the joists prior to adding the MDF, you'll be amazed how stiff and flat it is. By the way screw the bottom sheet to the joists counter sinking the heads 1/4" then surface it removing about .003 or enough to remove all the imperfections. then GLUE the next sheet and screw it about every 6" and all the way around the perimeter. the next day, remove the screws and surface the top so it's clean and you're ready to go. when the top layer is almost gone do the second step over again.

Good luck
Dave Patterson

[fleinbach]

Dave

what size table do you have?

[alabama_davo]

Hey Frank,
I have a prt96 and the table is 5x10

[mnrite@yahoo.com]

Dave
Did you cover the whole table with the MDF(5x10 sheets)more rigid I would think, or just the center (4x8 sheets) for ease of cleaning?

Thanks
Mike

[alabama_davo]

Hey Mike, I used 49x97 and that allows for fallout next to the rails.
I also indexed the table top and cut a groove in the x and y at 0,0 for the entire length of the table and installed stop blocks on the outside of the lines and reference my sheets to those blocks