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Hot Pipe Bending


Hot Pipe Bending

Shape wood with a propane torch.

By Garrett Glaser

Here's a simple, but effective way to bend thin stock (1/4" thick or less). The only tools you need are a length of 1-1/2" galvanized pipe, a propane torch, a jig to hold them both, and a fire extinguisher–just in case. The pipe is attached to a fl ange through a hole in 3/4" plywood. A jig securely holds the propane torch (Photo, above). This jig rests on the bench and clamps in a vise.

Any woods that take to steam bending are suitable for hot pipe bending, including oak, ash, elm, hickory, beech, birch, maple and walnut. Although there are exceptions, most softwoods and exotic woods are not good candidates. In general, air-dried wood bends more easily than kiln-dried wood. Kiln drying “sets” the adhesive compound between the wood fi bers (called lignin) in a way that makes it resistant to the softening eff ects of heat and moisture. This doesn’t mean kiln-dried wood is impossible to bend; bending it is just more diffi cult.

Always start by making test bends, using extra pieces from the same batch of blanks that you’ve prepared for the real McCoy. Having plenty of extra blanks is important, because you never know where a hidden weakness might lie, and watching a piece break when you don’t have a spare is a real bummer.

Soak in water overnight the pieces that you plan to bend. If you don’t have a large enough container to completely immerse the pieces, wrap them in a soaking-wet towel sealed in a plastic bag.

Ignite the torch, adjust the fl ame to low, and clamp the torch into position on the cradle, with its nozzle 1" or so inside the pipe. It will take a few minutes for the pipe to get suffi ciently hot. Test by dripping water onto the pipe. If the water boils in place, the pipe isn’t hot enough. When the water skitters off , you’re good to go (Photo, top right).

To create a tight curve, slowly rock the strip against the hot pipe with a seesaw motion and apply steady, gentle pressure until you feel the wood relax. Then increase the pressure. When the bend is near the end of the strip, hold the strip with Vise-Grip pliers to protect your hand from the hot (really, really hot!) pipe. To create a larger, more gradual curve, move the strip along the pipe in 1/2" increments, applying fi ve to ten seconds of pressure in each spot, just enough to feel the slightest bend. Check the fi t as you go (Photo, above). To unbend a curve that’s too sharp, simply fl ip the strip over . To make S-curves, work both sides of the strip.

To keep from scorching the wood, lift the strip off the pipe every fi fteen seconds (or any time the surface near the pipe begins to look dry) and quickly rewet it with a sponge before continuing. A little scorching is okay if the damaged surface will be hidden. But scorching can also ruin a piece; at the very least, it’ll require additional sanding.

As with steam bending, springback is likely to occur as the pieces dry. How much the piece moves depends upon a number of factors, including the type of wood used, the character of its grain, and the whims of fate.

This story originally appeared in American Woodworker August/September 2010, issue #149.

August/September 2010, issue #149

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Click on any of the images to view a larger version.

The pipe is ready when water droplets bounce off the surface. If the droplets stick and boil, the pipe isn’t hot enough.

This bending method resembles blacksmithing, because each piece is shaped to fi t, one curve at a time.