Torsion box question

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Forum topic by DonnyBahama posted 11-27-2021 09:36 PM 463 views 0 times favorited 6 replies Add to Favorites Watch
View DonnyBahama's profile


243 posts in 3864 days

11-27-2021 09:36 PM

Topic tags/keywords: torsion box assembly table

Torsion boxes never seem to be made with full length+full width cross members that use overlapping half notches. Is there a reason for that? It seems like it would be a much better way.

-- Founding member of the (un)Official LumberJock's Frugal Woodworking Society -

6 replies so far

View BlasterStumps's profile


2200 posts in 1772 days

#1 posted 11-27-2021 09:53 PM

?? I wouldn’t go all the way to “never”.

-- "I build for function first, looks second. Most times I never get around to looks." MIke in CO

View therealSteveN's profile


9383 posts in 1907 days

#2 posted 11-27-2021 11:21 PM

I agree.

Just looking at images on a duck search many of them are half lap, some are stringers and blocking.

Both end up with similar support, just the blocking ones may leave the top a little helter skelter, if not done well.

-- Think safe, be safe

View splintergroup's profile


6330 posts in 2555 days

#3 posted 11-27-2021 11:39 PM

Lap joints “help” but mechanical engineering speaking virtually all the bending loads are carried in the skins. The cross members carry the shear loads. If the attachment between the cross members and skins is good and complete, there is only a marginal gain in bending strength with half laps

View Fred Hargis's profile

Fred Hargis

7353 posts in 3826 days

#4 posted 11-28-2021 11:44 AM

I’ve built 2, and made both of them using 1/2 laps (or whatever you want to call those joints. It was easier (for me) and simplified construction.

-- Our village hasn't lost it's idiot, he was elected to congress.

View bondogaposis's profile


6095 posts in 3684 days

#5 posted 11-28-2021 03:03 PM

Torsion boxes are like 3D I-beams. The stiffness comes from the distance of separation between the skins. How that separation is achieved doesn’t matter so much.

-- Bondo Gaposis

View DonnyBahama's profile


243 posts in 3864 days

#6 posted 11-28-2021 03:21 PM

Thanks everyone! I’m glad to know that half lap notch joints work just as well. They sure do seem a lot quicker/easier to make and assemble. Thanks for the photo, @Fred Hargis! The little bit of OCD in me really prefers the way that looks! I know that no one will ever see it once it’s assembled But I particularly like the idea that each compartment has a known, repeatable dead center because I’m planning to put a hole in each one to accommodate these clamps (for glue-ups)…

-- Founding member of the (un)Official LumberJock's Frugal Woodworking Society -

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