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!
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