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We all know that wood is bent using steam... but how? over the kettle? Well I have tried and failed a few times.. untill I found a method like this. Steam bending is not all that difficult, it just requires patience. What I will describe will constitute a simple method that can be adapted to various sizes of wood and steam sources.

BUILD A STEAM BOX

Above I have illustrated the steam box that I have used with success a good few times. It consists of the following parts.

1) Saw horse (you can use one or two - more if so desired)
2) PVC Pipe - length and diameter depend on size of wood you are steaming.
3) End caps, PVC Cement, 'Clean out' end cap.
4) Metal Strapping
5) Small length of metal pipe (see description for size)
6) Rubber car radiator hose
7) Vessle to hold water (I used a petrol can)
8) Heat source (I used a camping stove)
9) Screws, drill, bits, screw driver

Construction

Select the PVC pipe of a diameter and length to acomodate the size of the wood you are going to be steaming Based upon this selection, choose an end cap that has a screw in cover which is of suitable size to fit the pipe you have chosen.

The cap and steam inlet for the other end is chosen the same way, but the fitting needs to be a 'cleanout' type fitting - this means that it has a smaller diameter tube which comes off the side - it
is to this that you will affix the radiator hose.

Cement the end caps fittings on, make sure you have the correct screw in fittings to close the ends (these do not get cemented on - they need to be removable to access the wood). In the bottom of the PVC pipe at the opposite end of the pipe from where the steam enters, drill a hole to allow the steam to escape. This forces steam to travel
along the length of the wood.

I initialy put the hole (as per the diagram) in the end cap, this is not a good idea, you run the risk of being scorched as you remove the cap.

Once this assembly is made, you can mount it across two sawhorses - or as I did, lay it across the width of one horse. This makes for more of a portable unit, though restricts the length of the piece you can steam. I did it because this was all the length I needed (was bending combings for kayak cockpits and hatches).

SOURCE OF STEAM

As I stated in my parts list, I used an old Coleman camp stove (you know, the ones that are prone to exploding) though you can use a propane stove, or hot plate, some people use tea-kettles with a large spout welded on. What you need to keep in mind is that you want a lot of steam, and you need to keep it coming for at least an hour (see table of steaming times at end of page). If you need to add water in the middle of the process you will run the risk of cooling the source water and stopping the steam flow untill all the new water starts to boil. I usualy keep a tea kettle boiling on the stove so I can add to the source water without cooling it.

As far as a vessle to boil water in - you can use most anything that is sealed with an outlet which will permit the attachment of a hose to duct steam into the steaming chamber - I use a 5 gallon 'Jerry Can' with a piece of pipe threaded to fit opening on top (most gas cans have a 'vent' that opens, you can use this to add boiling water if need be)

STEAMING

So as to get an even flow of steam all around the wood, you need to support the wood inside the pipe - this is easily accomplished using dowels cut to the width of the pipe and wedged in place - you can also drill holes through the pipe and put stainless or galvanized (you don't want them to rust) bolts through. Use caution if you go this route, the metal parts that stick out will get very hot - you may want to cover them some how. Also - keep an old set of salad tongs handy - these work well for reaching in and pulling out the boards you have steamed - by the way, WEAR GLOVES!!!

STEAMING TIMES -Or- HOW LONG DO I COOK THIS SUCKER

A few rules of thumb (for those of you who are all thumbs) are:

1) To bend wood you should steam it approximately 1 hour per inch of thickness
2) Exotic woods (Bubinga, Cocobolo etc…) do not bend well
3) Soft woods do not bend well.

When choosing the grain for the wood you are bending, it is best to bend along the grain of the wood, if you try to bend across the grain you are more likely to break the wood (though it is possible to bend it this way).

The following are some general dimensions to which some wood can be bent:

Ash............4.5” radius
Cherry.......6” radius
Elm...........2” radius
Hickory.....2” radius
Maple.......8” radius
Oak...........2” radius
Walnut......3” radius

To form the wood - you need to bend it on a mold - click here for some moldy information... Mold Making Info

Check this link for some excellent information about the moisture content of wood, green, dried, and
various stages of seasoning Click Here

ALTERNATE BENDING METHODS

Steaming is not the only way to bend wood - here I will present five alternative methods
which may or may not work for you, but for informative purposes they work just great.

Kerf Cutting

Should you need to put a bend in some wood that is more decorative than structural, you can bend it by placing a number of small
Kerf cuts on the back side (or side which will be compressed) which will serve two purposes. First is that it will relieve stress
on the wood allowing it to flex more, and second it will provide an area for the compressing wood to go (see illustration).
You can put some wood glue or other adhesive into the kerfs to help hold the bend, however, this type of bend is mostly used
where the back side (where the cuts are) is backed against something - a good example being moulding nailed to a curved wall.

Dry Heat

People have had success with bending thin pieces of wood using just heat. Various methods are used to supply the heat - you can use
a heat gun, a metal pipe warmed with a torch (not reccomended ie: fire/wood), hot water etc... the idea is to heat up the fibers and
make them elastic in this manner (moistening the wood will help transfer and hold the heat, this is sort of a cheap 'spot' steaming.
As you get the wood hot you then bend it around your mould. You are not going to be able to bend very thick wood, nor will you
get very tight bends.

Laminations

You can use thin boards which will bend easily on their own, but lack the dimension or strength you need. To remedy this situation you
can take several boards (I will use Luan plywood as an example - this is cut into strips 5" wide by 6' long, 3/16 to 1/4' thick)- on their
own these will bend to quite an extent, though they lack strength to make them at all structural. By bending one of these strips on a form
then glueing another strip on top of it, clamping that in place and allowing it to dry, you have made a stronger piece. You can keep adding
strips untill you have the correct dimension. Just remember to add a little length to each strip - you will loose length as you have further
to bend (lost in the radius).

Salt Water Soaking

Another method of making wood limber so as to bend it is that presented by the Viking ship builders - they would
soak their boards in a salt water bog or marsh for a day or two prior to attempting to bend them in to shape
on the form from which they were building their boats.

Generaly when boats were built at this time they were built from green lumber which has a very high moisture
content. What we get from lumber yards and hardware stores today is kiln dried. This lowers the moisture content
down to 25% give or take (will get some more difinitive numbers for you). Green lumber has the advantage of
more readily bending on its own (no steaming etc...), and it will not swell as much when the finished boat hits the
water. On the other hand, it will also shrink more and is more undpredictable when constructing something other
than a boat which will remain moist (ie: a table or book case).

Any way - the long and short of this is that the green lumber would be soaked in salt water to make it bend more
easily, an added benefit of this soaking is that the salt would start to pickle the wood and act as a preservative.
One last point: When it comes down to it, if you decide to steam wood, and think you want to use it, you will
have greater success steaming green lumber.

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