Figured maple is one of the most desirable woods used for the back and sides of acoustic guitars, but bending maple sides, or any curly or figured wood, can be tricky. These woods are often more likely to break during the bending process. You can avoid mishaps by going slowly and taking the precautions explained here.
What is figured wood? What we see as “curl” or “flame” is the movement of the grain line, where the grain goes up and down like a rollercoaster with alternating short and long grain. When you are bending wood, you are heating up the material that bonds the cells and fibers (grain) together. The heat causes these bonds to slip. When the wood cools, the board re-adheres in the new, bent shape. Because of the inconsistent length of the grain in figured wood, the short grain is not as well supported as the long grain. This lack of support predisposes the bond to slip abruptly when bending pressure is applied, causing an unfortunate break.
Some builders incorrectly believe that the more water you use in bending, the better. This is definitely not the case with figured woods (and is not really a good idea with any other wood). Soaking or boiling figured wood softens the short grain and further destabilizes the wood. Before bending, we recommend spraying the wood lightly from a spray bottle and letting it sit for a couple of minutes before bending. If necessary, spray it occasionally during the bending process to prevent the wood from scorching and to create a little steam which will help move heat into the material.
When hand-bending on a pipe or on our an electric free form iron, it helps to support the wood on the open side of the bend with a backing of some sort. A thin sheet of metal will help keep the grain ends from pulling up and will help to wood cool in the desired shape. Hold the metal on the outside of the piece and use it to help shape the wood. It helps to keep the ambient heat around the iron high by employing the use of a small space heater.
Mineral staining can be a problem when bending maple or other light colored woods (such as cypress or myrtle). If there are any trace minerals in the water you are using, the minerals will be left behind after the water evaporates. For this reason, be sure to use distilled water to avoid the black or blue discoloration.
If you are using the LMI Side Bending Machine, you are bound to minimize problems with trouble woods because the wood is supported by the bending form during the whole bending process. When we are using the bending machine in our shop, we avoid both scorching and mineral staining by covering the wood with baker’s paper (also called parchment paper –available in any grocery store). The paper should be white in color and have no waxy coating. Simply put one layer of paper on each side of the wood. A local archtop builder likes to wrap his sides in aluminum foil, which he says helps to keep the moisture and heat close to the wood.