Torsion Box Desktop: Mixed Materials?

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Forum topic by m88k posted 05-21-2010 12:04 AM 2484 views 0 times favorited 1 reply Add to Favorites Watch
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83 posts in 3148 days

05-21-2010 12:04 AM

I’m considering making the top of my new desk a torsion box. I think it will lend itself well to my plan for a modular design, and provide more stiffness than I’ll ever need. The desk surface is approximately 5’x2’, with probably a two inch filler. Just have a couple questions about using a torsion box:

1) If I use different materials on the top and bottom, will differing expansion rates cause trouble?

2) Is the expansion rate of the filler material important?

3) I’m planing on drilling holes into the box; does the inside need to be finished to avoid swelling?


4) What thickness would you run of hardwood plywood for the skin? The bookshelves supporting the top are all 3/4; can I move down to 1/2 for the top with a torsion box?

-- ~Mark

1 reply so far

View barryvabeach's profile


159 posts in 3240 days

#1 posted 05-21-2010 03:21 AM

Mark, I don’t think you should have a problem using different materials for the top and bottom, though I would stick with the same family ( such as ply ) If you used solid lumber for the top, and ply for the bottom, that could cause a problem. The expansion rate of the filler shouldn’t be a problem as long as it is uniform – I usually ply for the filler with no problem. I wouldn’t worry about drilling holes, moisture will go through the wood even if there are no holes and you finish it, so holes shouldn’t be a problem. You can get by with 1/2 or even 1/4 for the top, depending on how wide you space the grid. A 1/4 top though will give you a “hollow ” feel that you may not like. I would go with 1/2 for the top. As to grid spacing, I usually cut a small scrap of the top material and just lay it loosely over spacers that are various distances ( 3 inch grid, 4 inch grid ) and then press down to see how much sag I get. The actual torsion box will have less sag because it is glued to the spacers, but the test gives you a good idea that you can get away with some pretty wide spacing – even using 1/4 ply, and not get any deflection, so long a you don’t have any point loads.

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