Torsion Box Chicken or Egg Dilema!

[scott vroom]

OK, I'm becoming enligthened on the advantages of torsion box construction to obtain and maintain a dead flat table. My dilema is that I don't have an existing dead-flat surface upon which to construct the torsion box therefore I'm concerned that I'm going to end up with a torsion box that is not dead flat. How do you solve this dilema?

[David Wong]

Marc Spagnuolo at the Wood Whisperer has a great video (http://thewoodwhisperer.com/episode-18-assembly-table-torsion-box/) on construction of a torsion box assembly table.

[Mike Henderson]

I don't know how big you want to make the torsion box, but one way to do it is to "clamp" it in a vacuum bag. This will force the skins onto the webs evenly. If you cut the webs accurately, the box will be flat.

Other ideas:
1. Find a flat section of flooring and put your box on it when gluing. Then pile sacks of sand or other weight on top.

2. Use something like 3/4" MDF as a "press" on both sides (against the skins) and use cauls to apply pressure to the MDF to press the skins onto the webs. (this would be a difficult clamp up, however).

Mike

[johnny means]

If your webbing is ripped straight you should have no problem.

[Cory Hoehn]

Marc's video is great.

Another option: Take 2 or 3 2x4's and put them on top of sawhorses. Lay a couple of sheets of MDF on top of the 2x4's. Shim up the edges of the horses or the tops to make them perfectly level. Now you've got a temporary surface that will be a lot flatter than just putting it on the floor.

[Tony Bilello]

My first torsion box was built on 2 hollow core doors side by side and leveled. It was 4' X 8'

[Jim O'Dell]

I used my TS top with extension table. Don't know if the Torsion boxes came out perfectly flat, but they seem to be ok for what I do. Jim.

[Eric Gustafson]

Marc Spagnuolo at the Wood Whisperer has a great video (http://thewoodwhisperer.com/episode-18-assembly-table-torsion-box/) on construction of a torsion box assembly table.

+1 on Marc's video. It is the method I used when I built my assembly table. You can build a flat table on a couple of sawhorses using that method.

[Lee Schierer]

Check your suports with a level, the longer the better. You can use two saw horses for support. Just keep checking everything for level and square as you go.

[Cliff Rohrabacher]

My method guarantees you two flat surfaces.
I don't cut lots and lots of little block components to go in between the long strips.

I leave all the internal members long. That to say I have a bunch of 8" long by X" wide boards ( X being the thickness of the internal web). and a bunch of 4" long by X boards.
Then I lay them out and notch them so that they can be assembles in a Cartesian X-Y pattern.

This guarantees that the 3/8" thick 4*8 birch plywood I use to build the box skin will be pulled into conformity with the flatness of the webbing boards

In the spirit if a picture tells a thousand words:
http://www.sawmillcreek.org/showthread.php?t=64965&highlight=torsion

[Wayne Cannon]

Amen! If the stringers in both directions are full length, and ripped from plywood (as opposed to, say, 1x4s that can have crook), then it's hard to not end up with a flat surface.

The approach of cutting "lots of little block components to go in between the long strips" requires a flat surface on which to construct it and onto which it can be clamped, and seems that it could still warp if one skin were to expand or shrink more than the other in the dimension made up of little blocks.