Portable Torsion Box

[rick7938]

I have a small workshop that will not allow me to have a nice assembly table. I want to build a lightweight torsion box that I can store in my storage room and set up on saw horses on the carport when I need to use it.

I am thinking about building it from 1/2-inch MDF internal dividers and 1/2-inch MDF skins. I want the finished size to be about 36 X 60 inches.

My question: How thick do I need to make the torsion box, including the 2 - 1/2 inch skins to ensure that I have a nice, stiff work surface. I was thinking maybe 2 1/2-inches, but have never built one so I need some input and advice.

Thanks for any feedback.

 

[PeteM]

This might help;

http://thewoodwhisperer.tv/18-torsion-box-assembly-table/

pete

 

[cpw]

Rick,

Why not rethink your proposed design a bit and put more rigidity in the sawhorse base and use a hollow core door as the table top?

Check page 22 of this Google book Small Woodworking Shops to see what I mean.

 

[rick7938]

Thanks for the info, Pete and Charles.

I am probably going to have to use some of both concepts. The top is going to have to be detachable, but should be able to be adapted nicely to the improved saw horses.

Thanks again.

 

[rbdoby]

Rick,

If you build it all out of MDF you'll need to band the edges with something to protect the MDF. You may want to use plywood instead of MDF, I think it would be lighter than MDF.

Charles has a good idea with the hollow core door. If you cut it down to 60" you'll need fill the void between the veneers at the cut. Just mill a piece of 2x4 to slip fit and glue it in. Most hollow core doors I worked with are filled with cardboard, easy to clean out a space for the plug. You could also glue a skin of 1/2" MDF on the door if you don't think the veneer of the door would be strong enough.

You could always build something like this: http://www.blumtool.com/pages/benchhorse.html

Rick Doby

 

[Alan in Little Washington]

If you can wait until November there will be a comprehensive article in American Woodworking on how to build a torsion box written by one of our North Carolina Woodworker members.

I have built several torsion box tables. Without knowing your needs and usage I can't recommend materials, but will say this-

For economy of materials (two sheets) I used 1/2 MDF for the skins and webs for the 40" X 63" assembly table I built for the article (slightly more for the earlier, larger tables). The webs are 2" wide. Spacing was set at 7 1/4 inches so I could make the half lap joints in the long and short webs with the same setup. This is the way to go rather than how David Marks did it on his show and the Wood Whisperer copied - cutting and piecing). ( I have a thread that describes my earlier assembly table. 1/2" skins and web are HEAVY but strong and durable.

If you want a lighter, strong table, that may not be as durable, but easier to stow away, I would make it from a hollow core door or stronger 3/16 hardboard like the one I made below. Here is thread about it. It is 8' long, weighs only 30 lbs. but is shown supporting over 300 lbs of bricks in the middle of the span with only 1/2" of deflection. I think the webs were 2-1/2" wide and constructed with lapped joints also. It has open web sides since that was easier to do because it was too thin to brad nail sides on it.

The bottom line is you need to decide what you are going to do with the table- will you assemble stuff, will you be hammering stuff, will you need a web and skins strong enough so you can clamp things to it without crushing it.

 

[merrill77]

I just finished two 15x48" torsion boxes for a project. I used 3/4" MDF for the outsides - mostly because I was going to need to sink some screws in them. I used 1/4" MDF for the skins and grid and the top skin has plastic laminate on it. I'm amazed how stiff it is. Note that the design does not call for a lot of thickness in the skins and grid to get a very stiff box - that's the joy of the torsion design. The ability to take a lot of pounding is another story - MDF is pretty soft, so you might want something harder in areas you expect to take a lot of abuse.