Steam Bending Larger Boards

Advice on steam-bending 2x4 stock for a curved roof structure. October 19, 2013

Question (WOODWEB Member) :
I'm building a ceiling in a circular sanctuary which was designed to resemble a yurt. The main supports are 6x6 fir beams and the intermediate beams are full dimension 2x4 of a species to be determined. These intermediate pieces are about 10.5 feet long and are bent to a 5 ft. radius. I'm sure I'll get a chorus of replies telling me that glued-lamination is the way to go, but I'm trying to steam bend these for a number of reasons, including the challenge and the knowledge that I didn't use gallons of glue to hold them together. I've only bent smaller pieces of thinner wood before, so this is a jump for me, and I've got 24 of them to bend.

Does anyone have any experience doing this with a softwood like fir, cedar, pine or redwood? These woods are my preference for ease to acquire and work with and costů although I've heard that softwoods don't bend as well. I plan to experiment with different woods, but I'm still trying to get some advice from people who have walked this road before.

I'm planning to build a plywood steamer box big enough to hold 4 boards or so and then build several jigs. Assuming I'm cooking the boards for 2 hours, If I open the chamber and pull one board out to bend while leaving the others in there, will the chamber and thus the wood lose enough heat just in my opening the chamber that I'll need to heat them back up again or will they be good to go in 10 minutes after I've bent the first piece into place and gotten everything ready for the next?

Forum Responses
(Architectural Woodworking Forum)
From contributor B:
With material of that size, you will likely find more information on boat building sites. At least that is what people have said in past questions of this nature.

We've done a lot of steam bending with western red cedar and it has all gone very easily and come out well. This, though, was with 4/4 stock, but still doing multiple bends as you mention. If the box is only open for 10 to 15 seconds you will not see a big drop in temperature. The box will drop more than the wood.

We make our boxes out of 1 1/2" polyisocyanurate panels available at most lumber yards. They are covered on both sides with a foil like material and stand up well to the steam. They are easily cut to size on the table saw and can be held together with 16d galvanized nails pushed into the edges by hand. I think this type of box might be too weak for the size material you plan to use, but you could use it to wrap your plywood box. Insulating the steam box makes a big difference in performance.

From contributor D:
I will point out something you may not have caught yet, irrespective of how to bend 2x4 stock.

If your 6x6 run from the elevated center point to the top plate of the walls - radially, at pitch, and the intermediate 2x4 run from 6x to 6x concentric to the walls and sharing the same center point, then the 2x4 must be curved as a compound radius - not just a simple radius. This will complicate any bending you may have to do.

If you can't visualize how it works, try it as a mock up. Yes, I found out the hard way.

From contributor K:
I have made steam boxes where I only wanted a few feet of a long board steamed, which had little window holes cut through both sides. I could shove a board in, then chink around it with rags, steaming only the part I wanted to bend, rather than having to build BTU's in wood which didn't need bending.

I'm sure it would be better to get creative and make a good gasket to seal around it, but I was just experimenting, and it worked. You could do the same to just cycle new boards in, while pulling some out as they got ready.

However, I didn't think softwoods were all that good for steaming.

If this is your first attempt at steaming, please don't proceed without reading a good instruction manual. A good one can be found at, for free. No matter how much you know about wood, there is just too much involved to leave to intuition.

From Professor Gene Wengert, Sawing and Drying Forum technical advisor:
Flat sawn stock bends very poorly compared to Quartersawn. Most 2x softwoods will be flat sawn.