Torsion Box

[Howard Phillips]

Hello All,

I am planning on making a cutting and assembly table with a torsion box base. Originally I planned on going with MDF, however the table will be kept in an uninsulated garage and I'm worried the humidity may have an effect.

What materials do you recommend for this situation? Will MDF be alright?

If I'm making a 4.5' by 8.5' table, what spacing should I use for the supports?

Best options for the top?

While answering these questions, keep in mind that I will have to move the table frequently.

Thanks to all

[David Christopher]

Howard, you can use the MDF just seal it with BLO and wax or sanding sealer or anything to your likeing...as far as the spacing I made mine 6" by 6"

[Charlie Doret]

You might also choose to put laminate on both faces. If you'll use the table for glue-ups laminate is a good idea, as dried glue pops right off. It's fairly inexpensive, available at the big-box stores, easy to apply, and will do a good job of keeping moisture out.

[Jamie Buxton]

If you have to move the table a lot, MDF may not be the best choice. It is heavy. Plywood is lighter, and it is stiffer. I'd make that box with 1/2" ply for the top face, 1/4 inch ply for the bottom face, and either 1/4" or 1/2" ply for the spacer grid. I'd use 6" to 8" spacing for the grid.

To make the torsion box stiff and rigid, you make it thicker. For me, there's a thickness limit at about 6". I make the spacer grid with full-length and full-width slats. At the intersections I notch each slat half-way through, so the slats can pass by each other. Notching the slats can be done on a table saw. I have a 10" saw, which can cut almost 3" tall. Hence the 6" limit. If I wanted to make a thicker torsion box, I'd have to find some other way to cut the slots.

I cut the slots by ganging the slats together. I wrap the bundle of slats with that saran-wrap stuff intended for wrapping packages; office-supply places sell it. One of the nice things about the saran-wrap strategy is that you can put it anywhere along the slat bundle, and just cut through it if a slot happens to fall there.

[Mac McQuinn]

Why not use MDO? It's lighter, less toxic to work with, more stable in high moisture conditions and available at most Menards....I built a Re-loading bench out of it this spring in Torsion box style construction and really enjoyed working with the product. Since my back isn't what it use to be, I built it to break-down in (4) pieces. JMO

Mac

[Vince Shriver]

A set of good locking casters would make the table very mobile, regardless of its weight.

[Jim O'Dell]

I was told to be sure to make the top and bottom out of the same material, and best to be the same thickness. Reason being is that as temp and humidity make the wood move, and it will, if the 2 surfaces move differently, it will warp the box. I've also heard that the same surface should be applied to both top and bottom, so if using laminate, both need to be laminated. If just sealed with something, both sides sealed the same way. Although i built 3 torsion boxes with laminate on top and sides, and water based poly on the bottom, and have not had any problems in my unheated, uncooled shop for the last 2 years or so. Jim.

[Rick Lizek]

MDF will be fine. I've been making torsion boxes for many years following the guide lines of Ina Kirby who first wrote about them over 25 years ago In FWW. I had one I made over 20 years ago for my table saw between the fence rails that has stayed perfectly flat. Made of MDF about 4" tall with 5" grid spacing and 1/4" luan faces and vertical grade high pressure laminate. For several years about 15 years ago I had it stored in an unheated garage in Western MA. Still as flat as the day I made it. The grids were simply butt jointed and stapled to hold the frame together and the skins were glued to the grid in one operation with regular Tightbond glue. I've never made a torsion box with any kind of half laps. The beauty of torsion boxes is the strength and stability. Two other factors often overlooked is the speed of which they can be made and the other virtue is the fact they can be made very light weight by using pine for the core grid.
Ken Horner's book is an absolute must for torsion box construction...
MORE Woodworkers' Essential Facts, Formulas & Short-Cuts: Hundreds of All New, No-Math Rules of Thumb Help You Figure it Out (Woodworker's Essentials & More series) (Paperback)

[Charlie Plesums]

The grid is to hold the two faces the same distance apart, and do not provide any support across the box. Glue is your friend in making a torsion box. Therefore I put braces all the way across, then fill in with braces that are staggered just enough to shoot a nail through the long brace into the end of the filler brace, to hold it in place while the glue dries.

I would make the top and bottom out of the same material (ply or MDF), but not necessarily the same thickness. I often make beds with 1/4 inch ply top and bottom, but for a handicap bed, I use thicker ply on the top, because of the risk of point loads that might puncture a thin surface.