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.

Purchase this back issue.

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.