Tag Archives: silicone heat blanket

The bamboo guitar Part 4 – bending the sides

I use a mould and heat blanket to bend my sides rather than try to do it freehand with a heated pipe. Lately I’ve been thinking about trying a temperature-controlled electric bending pipe instead, in the hope (or is it delusion?) that it might give me more control over the final curvature.

When people ask how I bend the sides, I tell them I use a bender. Here’s what I think flashes through their minds before they hit me for being a smart-arse:


No, but seriously folks, people are often overly impressed by bent sides on a guitar. It was the thing that intimidated me the most when I started building, I know, but I’ve found that while there’s a very bountiful source of possible stupid mistakes available to choose from, it’s actually not that hard.

My side bender is a hollow mould on a base, with a waist clamp to draw the wood down into the concave bend and two clamps each at the head and tail to draw the side around the convex curves:


The sides of the mould define the shape, and it’s useful to slightly exaggerate the curves because the bent wood always springs back a bit when it’s removed. Around the edge of the mould you can see the ends of the rods that go from from one side to the other to form the actual bending surface.

The clamps are made from threaded rod and wingnuts from the hardware shop. You can’t see the end clamps that pull the front and back downwards to put the whole piece under tension, but they’re just eyebolts with a wingnut on each that act on the undersurface of the mould base.

There is a thin metal sheet above and below the wood that make up a metal/wood/metal sandwich to stop the grain breaking around the top surface, which is under tension. I use aluminium, though springy stainless steel is better in some ways but very hard to work.

Here are the first two metal/bamboo layers of the sandwich, ready for the blanket and then the second metal sheet on top. I put baking paper in between and give it a squirt of water to help the bend:


The heat is provided by a silicone rubber thermal blanket connected to a temperature controller. In the picture below you can see the thermocouple temperature sensor and the controller that allows heater to work safely and accurately.


Here is what the bent side looked like after the first attempt at 180 degrees C, which is what the manufacturers recommend. You can see that the waist doesn’t conform to the mould shape at all well, so I had to re-bend it several times at higher temperatures before it came right, ending up at 230 degrees:


Here is one bent side clamped into the building half-mould while still warm to allow it to keep the bend:


The bamboo behaved really well during the bending, and showed no sign of delaminating. So far, so good.

In my scheme of things, the next job is to make up the laminated top linings and fit them.