How to Make a Steambox for Bending Wood




Introduction: How to Make a Steambox for Bending Wood

skin on frame kayak builder since 1987

A steam box is a handy way to heat wood so that it becomes more pliable than it is at room temperature. Once pliable, you can bend the wood into shapes that you couldn't bend it into cold. Size of the steam box depends on the length and diameter of the wood that you intend to bend. In general, it's good to make the steam box just a little larger than the wood that you're trying to heat. The smaller the steam box, the faster it heats up and the sooner you're bending wood.
I use a short steam box for bending ribs for kayaks. The ribs are 1/4 inch thick and 3/4 inches wide and usually less than two foot long. I use a long steam box for steaming coamings that go around the cockpit of the kayak. The wood for the coamings is about 7 feet long and 3/4 inches by 1-1/2 inches in cross section.

Step 1: Materials List

You will need 5/8 inch or 3/4 inch plywood in the appropriate length. Thinner plywood would work but loses heat too quickly unless you add insulation to the outside of the steam box.
You will need a coat hanger or a few feet of heavy wire as supports inside the steam box to keep the wood off the bottom so heat can get to it from all sides.
You will need a cooking pot. A two quart size is good for starters. You can fill it two thirds full and generate steam for several hours.
You will need a heat source. If you plan on working outdoors, a camping stove works fine. If you work indoors, you can use a hotplate. The hotplate I use runs 750 watts. That is hot enough for the three foot steambox I use and just hot enough for the 8 foot steam box.
Since first writing this Instructable, I have gotten my hands on a wallpaper steamer.  It works much better than boiling water on a hotplate, mostly because it runs at a higher wattage and puts out more heat.  If you can get a used one, go for it. 

Step 2: Construct the Steam Box

Cut the plywood to the dimensions that you need. The interior of the steam box should be large enough so that when you load it up with wood there will still be an inch of space around the wood so that the steam can get to the wood.
Nail or screw the 4 sides together.
Close off one end of the box. Leave the other end open.
Screw a piece of plywood that is 4 inches wider than the diameter of your cooking pot to the capped off end of the steam box.
Cut a hole in the center of the piece of plywood so steam can get from the cooking pot into the steam box.

Step 3: Add Wires to Support Your Wood

Drill some holes in the side of the box to run your wire supports through. Keep the holes the same diameter as the wire to minimize the amount of steam that escapes or the need to do a lot of caulking. The wires will elevate the wood in the box so the steam can get to all sides of it. Cut wires 4 inches longer than the diameter of the box. Run the wire through the holes and bend over the ends so the wires don't fall out.
Finding the hole at the far side by feel is tricky. Shine a light in the open end of the box and look through the hole that you are aiming the wire for. When the light disappears, you have found the hole.

Step 4: Add Legs to Support the Open End of Your Steambox

Set your pot up on the heater that you will be using. Screw some legs to the sides of the open end of the box so that it is level with the top of the pot. The level steam box is important so that the lid of the steam box makes a good seal with the top of the cooking pot.
If you're not that ambitious, you can just pile stuff under the open end of the steambox to raise it to the right elevation.

Step 5: Steam Away

When you're all set, fill your pot two thirds full of water, turn on the heater and wait for the water to boil. After the water has come to a boil, the steam box still takes a little while to heat up. Once you get a good flow of steam coming out of the end of the box, you're ready to heat and bend. One quarter inch thick ribs heat up in under 5 minutes. Thicker stock takes longer. Heat has to travel from the surface of the wood to the interior. Rule of thumb is 15 minutes of heating per 1/2 inch of thickness.
Keep in mind that some woods bend better than others. White oak, red oak, ash and poplar all bend well. Straight grain is important as well. If you have rain running out of the face of the board, your wood will most likely break where the grain runs out.

It's really easy to leave on the heat when you're done bending wood. Eventually, the water all evaporates, the pot becomes hot and the plywood starts smoking. Good way to start a fire.



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    113 Discussions

    I have parts and pieces at my disposal that would allow me to make a steam tube that would SAFELY hold 2-3 psi of pressure in the tube. This would allow for a higher temperature, 216-220°F compared to 212 in addition to putting some actual pressure on the wood making for a theoretically quicker steaming time. That's my theory anyway. I was wondering if you know of anyone who has tried this approach? Am I wasting time? The wood I want to bend is approximately 1" thick. Any suggestions or thoughts would be greatly appreciated.

    Hi- would there be a problem if you inverted the box ~ so the parts dangle from hooks- hooks just located in the ends ~ no need to make holes for a rack like system?

    Could a steam box be used to straighten a warped guitar neck? I would think that a box could be constructed that would contain only the neck portion that needs to be straightened, and which allows the guitar body and the head where the tuning pegs are to extend out opposite ends of the box. Would there be an easier way? Also, it might be tricky to get it to cool to retain a true and straight shape. A straight jig would be important I'm sure. Anything else? Or is the whole idea just a waste of time, trying to fix something that is already toast?

    Thanks, pquin3

    6 replies

    I saw a technique for bending the sides of the body of a musical instrument using a wet rag around a large soldering iron. The wood is worked back and forth across the saturated cloth covered iron while applying pressure to bend it around the iron. I haven't actually tried this but it seemed like a good way to only apply the steam to the area of the bend.

    The question I would ask would be, what caused the neck to warp in the first place? If it started out straight, then warped, then is steamed back into position, what will stop it from warping again?

    Your scheme for straightening the neck via steam and then locking it into a straight shape might work. And if it does, you would be the world expert and could write an instructable about it.

    On the other hand, dried wood does not steam bend as well as wet wood or green wood, I assume guitar necks are made from well seasoned wood. Might be easier just to put a new neck on the guitar.

    no actually it wouldnt be easier to put a new neck on the guitar because each neck is different they make them from different types of wood but thats besides the point....necks come in different sizes, then neck you have could be 3" x 4" where it screws to the body and be a 22 fret neck and you could go buy one and it be 3.5" x 4" where it screws on and also be a 22 fret neck plus taking the neck off a guitar isnt good for the body itself...i would take a piece of pbc pipe that has a big enough diameter for your guitar neck to fit in and is about 5 inches longer than the neck, seal one end of it up pretty good (ducktape a trash bag to the end) then place your guitar neck in it hang something that will provide water vapor in to the pipe (i.e. an electric kettle/ also make sure to tilte the pipe with the sealed end sticking up that way the water vapor goes into it), then ducktape a trash bag to the other end but not all the way around only bout halfway around the pipe, and then place a thick blanket over the whole thing to provide insulation and then when the neck is nice and moist go take it and brace it straight (you could take two peices of 2x4 that are the length of the neck and place one on the top and one on the bottom then take two clamps and clamp then together tighly to hold them tight place one clamp on the right side of the neck at the top and the other clamp on the left side at the bottom to even out the pressure pretty well) and let the neck sit and when the water vapor evaporates from the neck you should be good!!!

    and yah, if your neck is warped then its a pretty crapy neck cause it should warp but maybe 1/8" if it does warped and not even that much the truss rod in it shoul keep it straight thats what its there for, so that the tension of the strings doesnt bend and warped the neck or eventually cause the neck to either theres no truss rod in it or you have a very crapy neck or your neck has a crappy truss rod

    I have to replace my oil fired steam furnace this fall. I was thinking of setting up a valve system allowing me to use it to steam wood all year round. Wouldn't be to hard to do. Auto water feed and such. Might b too much steam. Any thoughts?

    4 replies

    Temperature of the steam depends on what sort of pressure your heating system is at. Primitive steam source of the type I've illustrated operates at atmospheric pressure and the steam is somewhere around 212 degrees, hot enough to bend wood but not so hot that you're in danger of getting hurt. As long as you have a way of keeping your heat chamber at atmospheric pressure, you should be alright.

    Thanks for the reply, I'm very new here. Sleeping on this concept last night I thought I might be producing to much steam. Or waisting oil. Any suggestions for a type of hose to run from the back of my house to the shop, about 40'?

    Distance between steam source and steam box is your enemy. Unless very elaborately insulated you might end up with hot water at the end of the line, or at least a significant amount of condensate.

    Forty-feet! Really? It would need to be steam-pipe just like the stuff that carries steam to the radiators (for instance). Iron pipe? And, if it needs to span forty feet, think of several inches of insulation unless you want to fill your steam box with hot water.

    Would foil wrapped around the end with rubberbands to keep it tight work better than a towel?

    Is mahogany good for bending? I am constructing an arched arbor for our wedding and am thinking of using a steam box. My other thought, to have less waste, was to have the wood for the arch mimic puzzle pieces. Any thoughts?

    Hi can I use a pressure cooker as a boiler for the steam?


    2 replies

    A Home Pressure Cooker comes with a relief valve designed to allow steam to exit before the pressure builds sufficiently to deform or 'blow' the cooker.

    I suspect a copper tube could be fitted to this orifice to carry steam to your steam box.

    Not sure of the advantage - save the locking lid allows for piping all the steam generated provided you can create a steam-tight conduit. between cooker and steam box.

    yeah, presuming the pressure cooker has some place to hook a hose up to that lets you transfer the steam to the steam box.

    I'd like to make a Crumhorn, and doing so requires bending a length of wood with a hole drilled through it. Have you ever tried something like this, bending a tube with a hole? I feel like it should work, but I'd rather know for certain before trying it...