** CAUTION **
Using a steam box to bend wood is potentially dangerous. Adding steam to any type of enclosed space creates potential for dangerous situations due to the high pressure and "steaming" hot vapors and liquid. Ensure that you have a place for steam to escape. The following information is provided knowing that you are intelligent enough to make your own safety decisions. Building a teardrop trailer does not require steam bending wood. I am going for a unique look, and have decided to attempt this method. Please do not try this at home without taking safety precautions.
Building a DIY SteamboxMy grand teardrop design is a woodie, which means that the exterior has the wood showing, versus what many people do by skinning it with aluminum. My design calls for bending wood to match the shape of the teardrop. In order for me to accomplish that, I need to construct a Steambox. I have multiple lengths of wood that need to be used, so my steambox will be modular. I'll build the 1st section at around 6 feet long to accommodate the shorter wood that needs to be cut. Here are the supplies you'll need:
4 - 6'x6"x1/2" boards
1 - 1/2 Sheet of Pink insulation
1 - Steamer (Earlex Steam Generator)
9' - 1/4" Wooden Dowels
1 - Thermometer
50+ - 1 1/4" Exterior Grade Screws
Once the box is ready for steam, you'll also need these items
1 - Thick Leather Work Gloves
1 - Safety Glasses
6+ - Clamps
I'm not sure how much the insulation will help, and I didn't do a very good job of cutting it straight, so there are some gaps. It's my understanding that you probably don't want a super air-tight steam box, and you do want some vapor to escape, or you're likely to end up with an exploding box.
The Earlex steam generator came with a brass fitting the I've attached to the box almost in the middle.
I used wooded dowels spaced about 7" apart. These will help keep the wood raised so that the steam can reach all sides better.
A look inside the box with the dowels attached.
I purchased a cheap kitchen thermometer so that I would know how hot the inside of the box gets. I used aluminum tape to seal all the edges.
Here is my test piece of Red Oak inside the box. You can see the probe of the thermometer to the right.
Testing DIY SteamboxHere is the steamer connected and a towel stuffed in the end to close off the box.
General rule of humb is 1 hour for every inch of thickness of wook that you're steaming. Mine wasn't that thick, but I also didn't soak it ahead of time. I didn't realize that I would finish the box so quickly, and decided that I couldn't wait to try my hand at bending wood. On my next test, I plan on soaking the wood overnight, and then try a shorter steam time, since my wood was just under 1/4" thick.
Here is a timelapse of the temperature gauge. Not all that interesting, but I wanted to see how quickly the box heated up, and what that average temperature was. It hovered just around 215 degrees for most of the time.
I created a template to bend the wood around using parts that were cut on the CNC machine out of 3/4" signboard. Glued together, this will become where I clamp the wood after it comes out of the steamer.
Example of Tongue box lid bending form
I did record my first bending attempt, and here are a few screen shots of me attaching the steamed red oak to the template.
I'll probably keep this in the clamps for almost a week before removing. In the meantime, I have a few more templates to build. Successful first attempt at steam bending! I may try using a metal strap on the outside of the wood as well, as research shows that it compresses the inside wall of the wood more than expanding the outside edge, thus leading to less breakage.
I'll post pictures when I take the test piece out of the mold template.
Edit: 04.25.13 Poplar Test Piece
I steamed a test piece of Poplar last night. I soaked the wood for about 30 minutes before I had the steamer all warmed up. Not sure if that helped or not. The wood was in the steam box for about 40 minutes, where the internal temperature got up to about 210 degrees. The wood was very bendy and flexed about the 90 degree bend without much effort. I've finally ordered my planer, so I should be able to test a few more wood options this weekend.