Does anyone have any experience using heat alone to soften wood to take a
bend? I know the method of choice is usually steam bending, but I heard
tell that heat alone can also soften at least some woods enough to take at
least a gentle curvature. Any comments?
Typically, just heating relies on the moisture content in the wood. What
type of wood, how thick, which direction does the grain go (in relation to
the bend), and how much of a bend? Sometimes it's possible to "torture"
bend (i.e. just muscle it, clamp it, and rely on glue/fasteners (and time)
to hold it.) If one side is hidden, sometimes it's possible to cut kerfs to
get a bend. A steambox is moderately simple these days with large diameter
pvc pipe and an old pressure cooker or even a teapot. Even steam bending
isn't a guarantee the wood will like the bend, though.
It's true. For fairly small and thin pieces a heat gun will do the job. A
steam iron is good too. And at least as late as the 80's, Turkish wooden
boatbuilders used heat to bend thick planking and timbers on boats in the
60-foot range. This I saw in a feature article in the Woodenboat magazine
back in those days. I think I sort of remember that they built beds of coals
and hung the wood over the heat. Or something like that. In fact, if you
think about it, a steam box - the usual way to soften frame timbers for
wooden boat construction - is really just a heater, that happens to wet the
wood as well. Perhaps it would work as well if you kept the wood away from
Lots of boatbuilding and repairing is done with neither heat nor steam.
Mahogany planks 2" thick and 8-12" wide... screw it down at one end (into 2
or 3 ribs) and then progressively work your way down the the other end. The
screws are tight in rib 1 and 2 and not quite tight in rib 3. On day 3,
drive rib 3 home and start rib 4 and 5. The next day, tighten 4 and 5 and
start 6 and 7... and so on. Typically, repairs like this are done in the
dead of winter when the boat is hauled out anyway (well, in Maryland at
least), but I've seen it done this way in August also when the boat is not
safe without the repair. The only time I've ever done it was the winter
when there may have been humidity but there sure wasn't any heat.
Yeah, I see a lot of cold bending of planks here in Port Townsend. There are
a lot of little old 30-40' fishing boats around here with tight little round
canoe sterns, and it's interesting to see an inch and a half or two inch
thick plank being bent cold around from the centerline at the aft ends,
around a curve that you'd swear the wood wouldn't take without a tension
break on the face. Cedar sometimes, or larch, or fir. It would be rare to
see anyone using a steam box for planking around here. You do however see it
once in a while for frames if the boat has a lot of shape to it. The Turks
that I was talking about were using this for stringers and sheer clamps and
such in pretty good-sized timbers if I remember correctly.
You're a shipwright?
Nah... just a cheapskate that has owned a few boats. But, I know how to
pay attention around the boatyard. A good thing because cheap boats need
repairs. I haven't had a plank boat in 20 years or so. A few years ago, I
built a couple tiny "tortured plywood" kayaks.
Heat bending is what is generally used for bending of wood for acoustic
guitar sides (which are around 1/8" thick). It definitely takes some
moisture but surprisingly little - just some "spritzes" from a squirt bottle
are usually sufficient. Then the wood piece is pushed up against a heat iron
(usually an oblong curved pipe) and moved back and forth across the iron
with hand pressure to start the bending process. The iron provides the heat
as well as the counterforce to your hand pressure to create the bend. The
shape of the heated iron plus your back and forth movement over the iron
with the wood helps determine how sharp you can bend the wood. And some
woods bend better than others (good quartersawn grain is most definitely a
plus for this).
For thin woods, a steam box is often overkill and this type of hand process
is pretty easy to do. If you look on youtube you can find a bunch of videos
of people bending guitar sides like this.
Gary in KC
Wood fibers get flexible with water or better yet, heat and water or
stream swells the fibers (almost like feathers) as they take up water.
As the wood dries, the frayed fibers lock together again and the wood
retains (some) of its shape. I guess adding heat alone to green wood
will give some flexibility, but I have serious doubts that dry wood
becomes more flexible as temperature increases.
I just returned from a local woodworking show which arrives annually. One
vendor had a 1/8" thick wood stock about an inch wide and was bending it
using water and a round (I would guess a 1.5" or 2" diameter) heating iron.
He suggested sticking with the thinner wood no more than 1/4". He had many
samples on his table and all the arches/bends were clean, solid and still
hard, though some had a few minor char marks, but could be sanded. There was
no indication of wood expansion from water. They all looked good to me.
Using anything thinker would obviously require steam.
I have an old copy of Woodenboat which has an article by David
Peebles, in which he describes his methods of successfully bending
wood using heat alone.
He goes in to considerable detail as to various types and sizes of
wood he has bent and the numerous heat sources he used. (One of the
timbers was 1" x 1/2" seasoned oak which he reports as having bent
to form S shaped bulhead edgings for a 21' cutter.)
If you wish to track down the article, it's in the March '96 edition
of Woodenboat, issue Number 129.
Depending on what you trying to do is a big factor. the sides of a guitar
are bent with heat. If you want to try some heat bending get a piece of
wood about 1/8" thick. Clamp a 2" piece of pipe to a bench ( a 12" piece of
copper works best ) then heat the pipe with a torch ( map gas) get a spray
bottle of water spray the wood start rocking over the pipe won't take long
you will get a fell for it. keep the pipe hot wear cloves.
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