Flatness of double-layer MDF vs. torsion box

In a given area, MDF can be impressively flat but a full sheet may not be so flat because of exposure or storage errors or mishandling.

If you had two identically cupped 3/4” sheets, and glued them together convex to convex, you might have all you are thinking you need.

The unflatness in a given sheet diminishes with thickness. Therefore, I’d suggest 1” piece of MDF if you really think that much mass is required.

I have been working off the same assembly table top of 3/4 particle board for about 17 years. There is some webbing underneath. It is screwed down from the top. Pretty practical all in all, and it’s never failed or broken or even talked back to me.

Kindly,

Lee

-- "...in his brain, which is as dry as the remainder biscuit after a voyage, he hath strange places cramm'd with observation, the which he vents in mangled forms." --Shakespeare, "As You Like It"

Thanks Lee…sounds like I’m splitting hairs. :)

-- Optimists are usually disappointed. Pessimists are either right or pleasantly surprised. I tend to be a disappointed pessimist.

I am not obsessed with dead flat either, although there are a few times when you need a perfectly flat surface.

I have not used MDF alone, but have used laminate on both sides of a single 3/4” mdf sheet for a great layout and assembly table. Glue comes right off and it stays very flat.

-- Randy "You are judged as much by the questions you ask as the answers you give..."

I’ve always wanted to build a torsion box since I watched David Marks build one on Wood Works; however, I find myself using a solid slab door instead. I could make my project dead flat but to be honest, I haven’t found a perfectly flat service in my house or anyone elses! :o)

-- Mike... It's a big mistake to allow any woodworking tool to realize that you are in a hurry.

What is a torsion box that doesn’t have the bottom skin? That is what I do. Simple torsion boxes are actually pretty easy to make with pocket hole screws, especially if you leave off the bottom skin. If you can rip straight and parallel you can get good results. But you do use up plenty of screws. I prefer 3/4” plywood because it is lighter and tougher, and the torsion box frame is sufficient to pull it flat. Extend the top 3” or so beyond the frame if you want to have easy clamping. Don’t use glue (and leave off the bottom skin) and it is easy to go back and shim the low spots if they annoy you (now or later).

-- Greg D.