For a commissioned sculpture I needed to bend some lengths of pine in a 90 degree arc. To do that I researched both kerf bending and steam bending and ultimately settled on steam bending. Now I had to figure out how to make a box that could stand up to a few weeks of solid use. After a few tutorials I settled on the following design.
**Full disclosure -- I had fully made and used the steam box when a friend told me about the awesomeness that is Instructables.com so I had to unassemble and photograph the process. This is why certain parts of the wood is already stained and why I can't go back further in the progress as I wood glued parts together.**
Step 1: Ingredients
4 - 14" x 60" pieces of plywood. (I used 1/4" but whatever you have on hand will do.)
2 - 14" x 14" pieces of plywood.
4 - 1" x 2" x 60" pieces of wood.
1 - pack of R13 insulation.
8 - 2" x 4" x 3.75" pieces of wood
1 - 6" x 60" piece of stove pipe
1 - cheap coffee can
1 - steam source (I used a Wagner Power Steamer 705, but whatever you have on hand will work)
2 - saw horses (optional)
Drill & Jigsaw (Table saw if plywood isn't yet cut.)
Step 2: Assemble the Skeleton
Using three of the large pieces of plywood and all 4 pieces of 1x2, create a three sided box with all 4 pieces of 1x2 in the 4 corners.
Attach 2 pieces of 2x4 per side to act as a guide for the stove pipe down the center.
Step 3: Prepare the Endcap
Take your coffee can and cut a whole in the bottom to fit whatever delivery method you choose. In my case I cut up a threaded piece of plastic that came with the power steamer and epoxied it onto the coffee can. Insert the coffee can onto the end of the stovepipe. This can be hard to change once completed so be sure it's what/where you want it.
Step 4: Put the Meat on the Bones
Put the first two layers of insulation in the bottom of the box, lining up the holes cut in the insulation.
Place the stovepipe in the center in line with the three guides.
Cut the insulation into four 60 inch pieces and make holes for 2x4 guides.
Your measurements for the sides will be different than mine, but you'll again cut four 60" pieces, and then cut them in half. Once that's done cut them to fit in between your guides and press them in between the pipe and the plywood.
Step 5: Finish the Box
Put the final two layers of insulation on the top and screw down the top piece of plywood. Take your two 14" x 14" pieces of plywood and cut a 6.25" circle right in the middle. Screw one onto the front and one onto the back.
Step 6: Steam and Bend Wood
Hook up your steam source and insert the wood you wish to bend. I also recommend placing something under the tail end of the box so the condensation can drip out of the front rather than pooling inside. Place a towel over the front opening but leave a small gap to allow steam to escape so it doesn't build up pressure. Be sure to steam it 15 minutes per 1/4" and you should be able to bend it to whatever you need. In this case I've made 90 degree bend over a 5 foot section.