The banjo is an incredibly flexible and resilient instrument. It takes on a wide variety of physical forms and can be found to produce a wide variety of sounds and music. A banjo may be constructed from a wooden spoon, a soda can, and a piece of thread. Yet again, a banjo may be constructed from a tree branch, a gourd, and an animal hide using only hand tools. A banjo may also be constructed from the finest of hardwoods, brass hardware, abalone shell, a variety of synthetic materials, and require a large shop for production. Choice of materials is very much related to the end goal that one wishes to arrive at.
Banjo wood should be easy to work, strong, and not too heavy. While violins, guitars, and many other stringed instruments prioritize the use of quality tone woods, as an instrument that uses a membrane (the head) for its tone generation, the banjo is somewhat freer to wander from the luthier’s standard materials. Regardless of the banjo’s membranophone status, the wood (or other material) used to construct the neck and rim of the banjo will have an impact on its tone.
Maple, walnut, and cherry are some common woods for banjo building. Other hardwoods and fruit woods may be suitable. Some builders choose to use alder, apple, ash, dogwood, mahogany, sycamore, and on and on. These woods are all acceptable. Pine, cedar, and spruce are softwoods that may not be durable enough. Oak and locust may be too dense and heavy, although they are quite strong. I have seen oak used for tack head banjo rims and have used it myself for gourd banjo necks.
There are varying qualities of wood in all species and that is part of what makes wood so fun, every piece is different! Maple can be found in hard and soft varieties. The difference in the density of hard and soft maple is significant! While soft maple carves easily, hard maple may dull tool edges rapidly. Straight grained walnut carves well but some walnut can be very knotty with whirling gran that makes carving very difficult.
Questions of which wood species aside, the builder may give some consideration to the balance of primary concerns: availability, creative vision, strength, and workability. Working with the material that is available can be very attractive. However, compromising other concerns may be undesirable. Just because there is a locust post in the old fence out back may not be a good justification for using it to make a banjo neck. It may be really tough to carve! But, then again, depending on the creative vision for the work, your relationship to the material, available tools, etc., the old locust post may be perfect for the job!
Ideally, banjo wood will be free of large knots, rot, termites, and voids. To read more about wood, check out Understanding Wood by R. Bruce Hoadley.
Green Lumber vs. Seasoned Lumber
When lumber is freshly cut into boards it often called “green” and that is not far from the truth. Green lumber can contain lots of moisture left over from the tree’s biological processes. Avoid using green lumber for the construction of a musical instrument or anything that requires stability. As wood dries out and loses moisture it tends to change shape significantly, bowing, cracking, shrinking, twisting, and warping can happen as wood dries out. Seasoned lumber is lumber that has been allowed to dry out for a while after having been milled into boards.
Among seasoned lumber there is a distinction between air-dried lumber and kiln dried lumber. Air-dried lumber is just that, it is lumber that has been allowed to dry by the action of natural air flow. Eighteen months is a typical minimum amount of time for air-drying lumber. Longer is better. Kiln drying processes use a large oven to heat lumber and cook moisture out of it in a short period of time. Kiln drying has the added benefit of killing any bugs that may be inhabiting the lumber. Even after air-drying or kiln drying, wood can re-absorb moisture if left in a damp environment. For building a precision instrument made from wood, like stringed instruments, it is desirable to seek the most dimensionally stable wood that can be found. Whether air-dried or kiln dried, five years is a good minimum amount of time to wait after milling. During this time it is bets if the material has been able to remain in dry environment protected from the weather.
Grain Orientation
Grain orientation refers to the relationship between the naturally occurring grain pattern of a piece of wood and the shape that piece of wood has been formed into by human hands. There are a few terms used in lumber and woodworking to describe grain orientation. When thinking in terms of wood that has been processed into boards, these terms refer to grain’s orientation to the widest face of the board.
- Quarter sawn – Growth rings are perpendicular, 90 degrees, to the face of the board.
- Rift sawn – Growth rings are somewhat perpendicular to the face of the board at 30 – 60 degrees.
- Flat sawn – Growth rings are roughly parallel to the face of the board.
- Slab cut – Growth ring orientation can vary across the width of the board.
Quarter sawn and rift sawn lumber have greater dimensional stability than flat sawn lumber. The radial and tangential planes of wood expand at different rates with the radial rate of expansion being less than tangential rate of expansion. Because of these differing rates of expansion, flat sawn lumber can be prone to warping along the length of the board and cupping across the width of the board. Quarter sawn and rift sawn materials are more stable because the grain is oriented to the surface of the board in a way that takes advantage of the lower rate of radial expansion.
In its natural environment the trunk of a tree grows in concentric circles. In the photo below we can see the concentric circles that are the growth rings of this tree. There is one ring for each year that a tree has been alive. The visual appearance of growth rings is caused by variation in the density of the wood fiber. “Early wood” is lighter in color and is called early wood because the tree is able to grow more quickly in the spring or early part of the year when there is more water. “Late wood” is darker in color and is denser than early wood because it forms slowly later in the growing season when water is less plentiful. We can tell the age of a tree by counting the growth rings. We can also see the medullary rays that look more like straight lines coming from the center of this stem.
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