Steam-Bending Wood for the Novice

by Dave Doner

Many of us may get into a situation with a boat project that requires wood be steamed. I had seen a few demonstrations of steam bending over the years and learned a bit on the Internet but was still a bit hesitant about the subject. I knew however, that sooner or later I was going to have to know more about it.

Sooner came a few months later when I brought my newly-acquired 1958 17’Chetek Dutchess lapstrake home and moved it into the garage. This was going to be my winter boat project and I was eager to begin.

After all the hardware and seat assemblies were removed, I took out the plywood flooring. Hmmmm! How odd! All of the ribs as well as the keelson were rotted… but just below the floor level! Since I didn’t peek under the floor before I bought the boat, I had no way of knowing. You can call this lesson what you will but something along the lines of “If it’s covered up, uncover it” seems appropriate. Be a detective before you make your offer to the seller! It will cut the acquisition price and give you a much more accurate picture of what the boats true condition is and what your ultimate scope of work will need to include.
So here I was, wanting to begin my project but realizing the time had come when I had to bite the steam bending bullet. What I am going to describe now is what I did to build a steam box that was quick and inexpensive. I won’t get into the discussion of many other things that have to be considered when setting out to bend wood including the type, grade, thickness, age and moisture content of the wood, need for special jigs, another set of hands, suitable clamps, & proper fasteners. Pre-soaking the wood, building the correct size box for your needs and getting some idea as to how much time to allow for sufficient steaming are also considerations which can’t be overlooked.

(Click on Photo for a larger version)

I constructed the steam box as diagramed for about $50. 1 had an old fuel oil can which I was able to clean out and use so I saved a few dollars. I am sure all of you thinking about building a steam box such as the one I built already have some of the requirements in your shop.

A few points: I used a gasket to provide a tight seal between the heating element and can. A small length of sheet metal and a couple of pop rivets secured the element to the side of the can. Position it low so low water won’t bum it out. I drilled a small hole through the insulation and into the tube for the thermometer and marked the location so I could again find it. The wood blocking stopper is only snugged up against the open end of the tube as the steam is being generated. This fairly loose fit prevents potentially excessive steam pressure build-up. Slope the tube slightly so condensate water drains out. I used a few shallow glass ash trays to rest the wood on to make sure I was getting good steam penetration on all wood surfaces. I used leather gloves to remove the very hot steamed wood from the box. Finally, you have only a matter of a few seconds to position your wood.

Pre-plan your work once the wood is removed, get help to speed things up if you to and work rapidly!

Eric Theship at Real Craft Boat Works in Chanhassen gave me a couple of additional considerations: Block plane the edges of your wood slightly before steaming to avoid plank damage and to cut down on splinters and breakage. Slightly round the bottom, leading edge of, for example, a rib being driven down into the bilge so that the steamed wood won’t catch on the inside plank edges. To avoid splitting the wood, fasteners should enter at right angles to the grain, Orient your wood properly before steaming.

After steaming heavy timbers, quickly prebend a bit to help the piece adjust to the hull contour. Finally, a quick slosh coat of raw linseed oil to the just-steamed (and after pre-bending) wood helps preserve as well as provide lubrication to the wood.

Once underway, it did not take long for the thermometer to start raising to100 degrees, then 150, on to 175 and then finally to about 210 degrees. It was sufficient to do a nice job on 5/8”thick green white oak ribs. There is lots of useful information available on the internet regarding steam bending as well as from other club members. This is an important feature of our club. All of us have something we can pass on to someone else.

In closing, make sure you do your homework and be sure you have taken into consideration all of the safety issues before you start building or steaming. A device utilizing pressurized steam in excess of 200 degrees has to be constructed and used properly Good luck!