Steam Bending

[Bruce Kassler]

Hi,
I am building an outdoor roof structure that requires two each 20' long beams that are 3.5" wide x 12" tall with a 20' horizontal radius (an arch on its side with the 3.5" on top and the 12" on the side). I would like to make it out of douglas fir. I was thinking about steam bending 2"x4" layers with the 3.5" side facing up and using marine glue to stack eight of them up to the 12" tall beam. Will the douglas fir work? If so, how long do I need to leave them in my steam tube? If not, any other ideas what would be best for this application? I thought of using my bandsaw and ripping and planing 1"x12" boards down to 3/8" thick and then bending and gluing 10 of those together. What do you guys think?

Bruce Kassler

[Loren Woirhaye]

That's a pretty gentle radius. I think you may find the following approach works. You may be able to skip the steaming and boil a bunch of water, sluicing it over the board in a bending jig with a come-along or similar apparatus at the ready. Pour the water on fast and pull the board into the bend as quickly as possible. You'll get the most reliable results using a steel backing strap and end stops, but of course that's a hassle to put together and perhaps you can get good results without it.

Do keep in mind knots are likely to be points where the bent boards will kink, so clear stock is the best choice.