http://gaboats.com/tutorials/steambox.html and http://www.bhs.is/zzzip/zzzip/ under "Keel, chine, and sheer."
I've been toying with using a PVC pipe for the steam chamber, and I know some folks use downspouts or any number of other materials. With the number of frames I'll be replacing, I wanted one with a little more capactiy, so I took a bunch of pine 1x material lying around that I got cheap. Using two 12' 1x6 boards, I cut them in half, and ended up with a box measuring 5.5" x 4" on the inside by 6' long (the maximum frame length is around 5'). The things I really liked about the "gaboats" steamer are that it uses 3" PVC pipe for the steam path from the boiler to the box for easy flow, and the idea of a plywood lid for a regular pot making up the boiler. How simple!
I had mine all made up by Saturday night, including a plywood lid for a big Revereware pot. I still had not settled on a heat source, however. My old gas grill had a side burner, but my current one does not. I don't have an electric hot plate. My brother-in-law has a big turkey fryer that I'm sure I could borrow if needed. Something my wife said made a light go on in my head... we have an old Dazey electric combination crockpot / deep fryer! For frying, the crockery liner comes out, and you're left with a heavyweight (1/4" thick or so) aluminum pot with a 1400 watt heating element embedded in the bottom. It has a removable dial thermostat that plugs into the pot, and the pot has bakelite feet to hold it off the ground. With that in mind, I quickly made up a new plywood lid for the new diameter pot, moved my plumbing over to it, and voila! Quick & easy!
First, a couple of shots of the entire rig. The box is simply screwed together with drywall screws.
Here it is broken down. I decided not to glue all of the plumbing together for the very reason of being able to do this.
Some plumbing details. I decided to use 3" toilet flanges to connect my pipe to the wood. I did glue the top elbow onto the toilet flange that enters the steambox, and I glued together the entire trap assembly. I wanted a way to add water to the system without providing a path for the steam to escape, so a trap seemed logical. However, I didn't want the trap to hold too much water that would be cooling off, so I reduced the pipe down to 3/4". The trap is simply a few "street elbows" joined together. The outermost piece is a 1.5"-3" reducer, which I thought would make a nice funnel for adding water. Some folks pre-heat the water they're adding so that it won't slow down the steaming process. I didn't want my trap to leak, so I glued all these parts together.
The nice side benefit of having this funnel and trap is that it happened to be in just the right position to catch condensation dripping out of the steam box. There's not a lot, but during my 45-minute test run, not a drop of water hit the floor from any point on the whole rig. Due to the very cheap lumber I used, the steam box ended up with a bit of a twist. This had the welcome benefit of creating a low spot on one side for the water to drip from.
Since you want steam to flow on all sides of your wood, you don't want it sitting on the bottom of the steambox. I added 1/2" dowels every foot or so near the bottom of the box. I also ran a second row about halfway up the box for a second shelf, increasing the amount of wood I can steam at a time. The holes go all the way through one side and partway through the other. The pins were hammered in after the box was assembled, with a touch of glue to hold them in place.
Here's the door assembly. It's just a short piece of 1x6 with a loosely set screw as a pivot hinge. The corner is rounded so that it clears the cleat screwed onto the side. The cleat both holds the door shut in one position and holds it open when swung around. The door should be somewhat loose to allow steam to escape. I realized that during steaming, the door will swell on the inside face, cupping the wood so that the exit is opened a little more than before. If this is a problem, I might make a plywood door to resist the cupping somewhat.
A short section of 1x6 cut at 10 degrees on the ends flares the two 1x6 legs nicely. Again, everything is held together with drywall screws.
Here's the plywood pot lid. I first traced around the outside of the pot onto the plywood. I then cut a circle about 1/4" inside that line. It was a still a little oversized to fit into the pot, so I trimmed it on the stationary belt/disc sander. Next, I took the outer piece of plywood with the circle still on it, and I cut just to the line. This made it fit nicely just outside the rim of the pot. Both pieces were glued onto another backing piece of 3/8" ply, and temporarily screwed together. Once dried, I removed the screws and marked it for the 3" center hole of the toilet flange, and I attached that with four screws.
Since I didn't glue all my plumbing together, I get a little leakage down the outside of my 3" pipe. Luckily, the toilet flange has a nice groove that catches this water. A couple of 1/4" holes drilled through the groove and plywood allow the water to drain right back into the pot. See the hole near the drywall screw in the center of the photo.
In my test run, I just added cold tap water periodically into the funnel. I never added more than about a cup at a time, but it didn't seem to slow the steam down much. In about 45 minutes of steaming, I added about a quart of water and ended up roughly where I started. Using this pot as a boiler really did a great job. The good thing is that if the pot did ever run dry, the thermostat would hold the pot to 250 degrees or whatever it's set to. I'm trying to come up with a good way to check or display the water level without taking the lid off. For now, I just listen to the sound as I add more water! I'm considering some sort of float through a hole in the plywood lid. Ideas, anyone?
Here are the two test pieces of maple that I did, around 3/4" square. I really did bend them agressively, and I think they had some grain runout which made them split, but not before taking a nice bend.
Hope this helps somebody out there. I have full-res copies of all the photos if it would help -- just let me know. The bottom line for me is that I was probably overthinking the problem, making it out to be harder than it really is. I've also found that there's a LOT of room for creativity & variability in how to build a steambox. I just had to have a pressing need for one before I actually got up and built it.
Cheers,
Bill
