Making a Steam Box

So I have decided I want to try and make some chairs. The design I want to go with requires steam bending some wood for the back legs similar to a Boggs style chair. This means my next project is going to be that I have to build a steam box.

The plan for my box is a simple plywood box that will be roughly 7"x 7"x 48" long with stainless steel rods passing through the sides to serve as a shelf for the pieces. I plan to use exterior plywood for the box and I was considering adding some rigid foam insulation on the outside to help hold the heat. I'm not sure if this foam insulation is necessary as it is not something I see a lot of. I would expect the steam to condense inside relatively quickly without some sort of insulation.

My big question and the reason for posting is about the steam generator. I bought an Earlex Steam Generator a while back for this purpose and I'm curious if this one generator would be enough for a box of this size. Is it worth trying to steam bend wood with just one of these generators or should I just add another Earlex to this box and call it a day?

Basically I'm just looking for any advice from others that are steam bending using this setup. Should I have two steam generators going to be sure I have good saturation or will one be fine? Am I missing something with this design or should I be looking at a different design all together? All advice would be greatly appreciated. This is a very new road I'm traveling down.

I've built a lot of chairs and a lot of steam bending of chair parts. Your steam generator looks a little small. This is what I used; I never built a box, I always used schedule 40 pipe. If you strap it to a 2x4 it will not sag, and when it does, who cares, get a new one. I used a turkey fryer stand and a gas can for water, (https://www.globalindustrial.com/p/s...oaAnYMEALw_wcB) and a radiator hose to move the steam.

I visited Brian Boggs a few years ago and on his high end chairs, (which one isn't) he does not steam bend the backs. He saw kerfs the backs, but only down until it gets straight. Then he glues in thin strips to fill in the saw kerfs and bends it all like a glue lamination. He says it give him more consistent results with almost no spring back. If you ever get down to Ashville, NC he's a great guy to talk to and his wife is easy on the eyes and also very knowledgeable.

I use a 120V wallpaper steamer for my steam box, which is around 8"x8"x36" and it works plenty fine for as long as I need it. I'd say see what your current steam generator can do before you get another one.

I just have 5/8 dowels to support the work. I put that foil backed insulation on the inside of my box, and it works, but the heat is a little too much for it I think. The outside of the box might work better, although you'll probably need to dry it out thoroughly to prevent mold.

If you haven't steam bent anything before, do a bunch of practice pieces before building anything to get the hang of it. It isn't hard, but it takes some time to figure out when the wood is ready to be bent, how far you can bend it, how much springback there is, etc. Also be careful of burns, especially steam burns. They happen quickly and often before you have time to react.

On page 6 of my boatbuilding thread "I'm finally building my boat," there is a bit on my steam box. I had to build one 8' long. It worked very well. Mine has dowels to hold the wood off the floor and keep it out of the water. The steamer is a turkey fryer and pot with a lid, and I cut a hole in the lid and fit a plastic tube. Don't get the ceramic coated pot like I did- get aluminum. A metal gas can would be nice. I didn't have access to one. Also you could cut a hole in a portable air tank and use that for the boiler.

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I've got the Earlex Steam Generator as well and built the box shown below (just a little under 52" x 7" x 7") out of cedar and either ACX or CDX plywood with 5/8" poplar dowel supports. If you follow Earlex's own recommendations (watch the related video), 60" X 6" x 6" (2,160 cu. in.) is about as big as you can go if you're just using one steam source like the Earlex. If you've got additional volume then you'll need two steam sources in order to provide a uniform distribution of heat and moisture. The temperature gauge was a cheapie from the local hardware store, but it helps to ensure that the box stays at temp for the duration of the cooking (about an hour per inch of material thickness). I also created a gasket around the door opening by spreading a thin layer of silicone, however, to prevent pressure buildup, you don't really want the box to be completely sealed. And, don't forget to include one or two drain holes somewhere in the bottom, so the condensed moisture can run out.

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You may have trouble with plywood. The moisture change is dramatic and may incur some drama in the plys. Use pine. Glue it with Gorilla glue or equal.

You will need to monitor temperature. It is surprising how long it takes from steam leaking out of the box till the inside temp at middle or bottom exceeds 200 F

5/16" dowels are adequate, but you may want to use 3/8"

I set mine up so the condensation drained back into the kettle. Better to feed it hot water slowly than to pour in a slug of cold.

I used a new round 2 gallon kerosine can for a kettle (didn't want to risk making a mistake with a gasoline can). Put a big restaurant burner under it. Made a tea cosy out of fiberglass cloth to contain the heat a little. (it's what was handy) It works fair. The steel does not transfer heat well. Better to use a big aluminum pot or a steam generator.

All this stuff was cumbersome so I built a cart with the burner and fuel tank on the bottom shelf. Put on two wheels and a handle. It resembles a long narrow barbecue. Made it narrow enough hoist up into the garage truss space. I use it about once every 3 years.

Have rebuilt the steam box from 12 x 12 x 60 with a hinge up lid (hard to seal) to the same but with access from the ends (better), to 6" PVC pipe 48" long (much better)

I have used 1 1/2" sheet foam to built my steam boxes. Cheap and easy to make.
I used deck screws to hold it together.


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Good luck with your project

Tim

I've used aluminum gutter for a steam box. Doesn't hold heat very well (aluminum conducts heat better than almost anything except copper or silver) but you flood it with steam and it works...

Following this thread because I'm curious. :)

I have the Earlex (Rockler) generator and my box is 6x6x48. It works fine. I used 'furniture grade' plywood only because i had that on hand. It's delaminating of course, but it still works just fine. You only have to gasket up the the lid.

My advice is don't spend too much time or money making the box perfect. Make it fit your pieces as well as possible. 6x6x48 is going to work fine for a typical chair (legs, headrest, etc).

For the back posts of the Galbert chair I'm making, the whole post is not bent - just a portion. So, I put the posts in and cram t-shirts around the gap. Even with this imperfect seal, it steams just fine. You may just have to go for a longer time. Galbert (on his blog) has some great tips for bending including using plastic wrap to increase the open time while you are bending.

I'll make my next one from a large pvc pipe.