A Semi-simple Steam Box

I’m making some chairs from an oak tree that was taken down in our back yard. These chairs require that some of the parts be steam bent. I’m starting with the simplest of the few chairs that I think I’ll be able to get out of this log, a post and rung rocker. The two long back posts need a gentle bend in the design I’m building. So I needed a steam box. I could have gone the simplest route and bought a PVC pipe and some end caps. That’s not my style though. I like wood.

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The materials for the steam box are pretty simple and available at any home center. There are two six foot 1 x 4s and to six foot 1 x 6s. Plus some nails (mine are cut finish nails), a few plumbing parts and some hinges (I ended up using different hinges).
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The parts to be steamed are supportd above the bottom of the box by some dowels so that the steam can circulate around them. These dowels were spaced about 6″ apart and placed about 1″ above the bottom of the box. Apparently either my 3/4″ auger is oversized (not likely) or this dowel was quite undersized (pretty typical of home center dowels).
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The box is just nailed together. There is no joinery at all as there’s really no need. I used cut finish nails. The end cap is rabbeted on all four sides to provide some resistance to racking.
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The end cap is, again, just nailed on with cut finish nails.
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Time to provide an entrance for the steam. I bored a hole about 1-1/4″ or 1-1/2″ (don’t remember which it was) in diameter. This hole is centered on the bottom of the box.
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Ovder the hole, I screwed a floor flange for iron pipe. This one is either a 3/4″ or 1″ floor flange, I don’t remember the exact size. Bigger is better as you want to fill the box with as much steam as possible. I used brass PEX connectors to attach the supply hose to the box.
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I used brass PEX connectors to attach the supply hose to the box and kettle. The hose is standard heater hose, available in most home centers or auto part stores. It’s designed for high temp applications. The hose is just attached to the PEX connectors with hose clamps so it can be easily disassembled.
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The door on the opposite end is made identically to the end cap. The only difference, obviously, is that it’s attached with hinges. I had to buy these hinges and bend them as the other ones I had didn’t work out. I also picked up a cheap pine knob. Looks nicer than the shiny handle in the first pic.
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Time to add some legs to get the box up above the kettle. I had my apprentice cut the leg stock. Look at that perfect grip on the saw and the proper stance and alignment! She makes a dad so proud :). She cut right to the line too.
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We screwed the legs that she cut to a 2 x 2 block of poplar and then attached them to the bottom of the box with the hinges from the first picture so that they could be folded up for storage. The front set of legs (closer to the door) is also 1″ shorter than the rear set so that the condensate inside the box will drain out rather than pool up inside the box.
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The tea kettle is just an old one that we had laying around. The PEX connector was driven into the spout with a mallet and the hose attached with a hose clamp. The electric burner is a $20 version from the big box store. The kettle will steam this box for at least 2 hours on a single fill of water. There was still plenty of water left when I was done, so I’m not sure how long it will actually go for.
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It works! These legs are shaved to about 1-1/2″ in diameter and they bent without any problem. Well, it took some muscle, but the ratchet straps pulled everything smoothly and the wood bent without any cracking. Granted this is a gentle bend, but it’s a good start.

So the next trial of the steam box will be some back bows and arm rails for a sack back Windsor chair (or two). While the stock for those parts is only on the order of 3/4″ thick or so, the bends are much more dramatic, so they’ll be a much better test of the steam box and the wood from this tree. I’m excited though. This is fun stuff!

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7 thoughts on “A Semi-simple Steam Box

  1. Thanks for the how to on the steam box Bob. I’ll be borrowing heavily from your design. 🙂

    Anxious to see some sack back action soon.

    Your daughter really looks like she knows what she’s doing with the saw. Wonder where she learned. Might wanna check your camera though. It must be shooting reverse negatives or something because it looks like she’s sawing wrong handed, er, I mean left handed. 😉

  2. Nicely done, elegant in its simplicity and performance. Very similar to the one I use for making Gragg chairs (yours is wa-a-a-y nicer). I simplified mine even further by using a wallpaper steamer screwed to the closed end Works like a charm. Have a post scheduled about this in two weeks.

    • Thanks Don! Looking forward to reading your post. I remember seeing your Gragg chair and steam box in APF and at WIA last year. Just stunning. Ever since seeing your talk on finishing last year I’ve been wanting to get my hands on a couple of your polissoirs. Speaking of which, I’m also looking forward to getting my hands on that other little French project of yours. Can’t wait to read that one.

  3. really nicely done. I have so much respect for people who take the time to make a tool like this just a little more special, and not take the easy way out. I like your style!

  4. I made one similar, but made it so that the condensate runs back to the steam inlet and back into the kettle to be re-cycled.
    This method works in the same way that old one-pipe steam heat systems did: the steam flows upward in the center of the pipe, and the condensate runs back into the boiler by clinging to the walls of the pipe.

    The connecting pipe needs to be at least 3/4″ like yours is.

    It also helped the process by wrapping the box with 1″ polystyrene insulation. I used the setup to bend pieces for a couple of oak rocking chairs.

  5. I used to think steam from my kettle and hot plate was just fine. Then I got to tryout a wallpaper steamer hooked up to my box. The bends were much more consistent and easier. Now I don’t think I can go back to the old way.

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