Wood Bending
By Tom Kindschi
A basic skill necessary for building any stringed instrument is the ability to bend wood for your instruments sides. Wood bending for furniture making and wood boat building utilizes a “steam chamber” to steam soften the wood before it is clamped into a form that holds the wood in place as it is drying. The thin side wood utilized in musical instruments could be damaged by over steaming so the technique utilized relies on a more localized “spot” steaming. This type of wood bending requires a “bending iron” and a form or “body mold” to hold the wood once it is bent to its approximate shape. Let me explain.
I build mandolins and dulcimers so my experience and advice is based upon building these instruments only, no guitars, violins etc. Side wood for both my mandolins and dulcimers is planed and finish sanded to a thickness of 1/10 of an inch. To prepare the wood for bending, I soak the side wood in warm water for about an hour or two. Once the wood has absorbed a little water it’s ready for bending.
You’ll need a bending iron. A bending iron consists of a rounded metal surface that is heated; as you gently press the wood against the heated surface is will steam and start to bend. Continued passes and pressure will continue to bend the wood. It is good to have a bucket of water handy to dip the wood in as you bend it as the absorbed water will tend to “steam out” as you make continued passes against the hot bending iron.
Luthier supply shops sell electric bending irons that you simply plug in and set to about 75% of the maximum heat. An alternative to purchasing the electric bending iron is building an iron by mounting a short length of 1-inch diameter iron pipe on a block of wood. Position a propane torch at one end of the pipe at a relatively low flame setting. Once the pipe is warm, you’re ready to bend. Just make sure that as you bend you are not standing in line with the open end of the pipe. During one of my first bending experiences I noticed an odd burning odor only to realize that the heat coming from the open end of the pipe was scorching my sweatshirt. So much for my favorite sweatshirt! I use both an electric and my homemade iron. They both have their place in your shop. Here’s a simple sketch of a bending iron that will cost only a few dollars to construct (not including the propane torch).
Some woods bend easier than others. Due to its variable grain characteristics, the most difficult is the “flame maple.” Building a dulcimer with straight-grained maple (hard of soft) is a good introduction to bending side wood due to the gentle curves of the sides. Walnut and Cherry are also preferred woods for dulcimers and are easy to bend into the gentle curves of the instrument.
To make a body mold for a dulcimer sides simply take a 2” X 4” or 2” X 6” and cut the desired shape of the side curves (plan view), centered on the 2” X 4”. Sand the cut surfaces smooth allowing for insertion of the 1/10” side wood. Once you’ve completed your bend you need to clamp the side wood in between the curved surfaces of your mold until it is completely dry.
The Roger Simminoff book Building a Bluegrass Mandolin is an excellent book with concise, well-written instructions. I highly recommend this book as it covers many building techniques, including body molds that can be applied to other instrument construction.
Hanging over my workbench are a few broken mandolin sides that represent many hours of work that ended in kindling. Here are a few tips to increase your wood bending success.
A fellow luthier gave me this tip years ago and said he used sheet lead, the type used is some old roof flashing. This lead can be difficult to find not to mention the toxic nature of the lead. I started out using pieces of thin galvanized metal and aluminum flashing cut to the width of the side wood and they worked fine. Luthier supply houses now sell a spring steel metal backing plate for a few dollars. They also work great and spring back to after each use.
A well designed precisely shaped mold for your side wood / body is essential; that will be a topic of future article.
Good Luck!
Tom Kindschi