Here’s a shot of my bookmatched sides ready to be bent:
Many luthiers shape an edge on each side with a compound curve before bending. This aids fitting the back and makes it a good idea to label everything before you get started. I’ll shape this edge after bending, but want to ensure the grain is as symmetrical as possible from bass to treble sides of the finished instrument.
Bending begins at the waist and I’ve marked this location approximately 14” from what will be the neck end.
With my bending iron plugged in, the dial is turned to the middle setting. Yellow cedar is pale in colour so I have to be more aware of scorching than if I were using a dark timber such as rosewood. Therefore I’m going to lay off higher heat until I’ve had more practice. Even at a lower setting the heating element inside the pipe gets red hot. It’s hot enough to bend when water pings off the surface rather than sizzles.
The side is given a generous spray of water and held against the hot pipe. Steady gentle pressure is applied until I feel the wood become flexible. This has been described as feeling the wood “relax”. Once the wood starts to give way, I apply more pressure whilst listening for the sound made by moisture evaporating on the hot metal. To avoid scorching, I use the spray bottle to keep the surface touching metal moist and keep the wood moving.
Any kinks can be corrected by selective heating on the opposite face.
I check the bend against a mold made of laminated mdf. When satisfied with the fit, I move on to the lower bout.
More checking against the mold. More bending.
After bending the upper and lower bouts I clamp the side into the mold to let the side cool off and dry out. As you can see, the side has been over bent at the ends. This is to allow for spring back as the wood tries to straighten itself out when removed from the bending iron. I again begin at the waist and realize very quickly that I should have made my mold much deeper. I was impatient and tired of large clouds of mdf dust. The clamps fit but it’s awkward.
I make it work and set the package aside to settle. After a day or two I’ll unclamp the side and touch up any irregularities until the side fits the mold perfectly without the need of clamps.
I must admit I was expecting this stage of the guitar build to be more difficult. Yellow cedar bends easily though, and tests on scrap wood helped me get a feel for the process. Enough of the test pieces snapped for me to recognize when I might be pushing the bend too hard.
All in all, I think things went rather well.