Heat bending of wood

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?
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Jim Willemin wrote:

Wood isn't plastic. Heating it is just going to make it harder.
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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.
Ed
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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 the moisture.
Tom

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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.
Ed
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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?
Tom
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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.
Ed
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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

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On Fri, 21 Nov 2008 08:27:37 -0600, Jim Willemin

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.
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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.
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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.
: )
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Bamboo, not much else. The trick is a very small flame and careful movement to control temperature. Spirit lamp is traditional.
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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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wrote:

Should I just soak it and go at it with a big "rosebud" propane torch? Bend it around a small truck rim?
Bending the grain the "long" way. Part is 4 feet long.
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Steam bending is the easiest way. Buy some ABS sewer pipe of sufficient size, drill a few exit holes in it and then just use a kettle to fill it with steam.
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