Aluminum
Continuing the theme of teaching, one aspect I love about lutherie is an opportunity to interact and share knowledge with other interested students of the craft, from all around the globe. Freely exchanging information about our explorations elevates the state of the art much more rapidly than was possible, pre-internet.
Expect to see the quality of instrument innovation improve, and design cycles shorten.
Alex Gorm Ost of The Aluminum T-Beam Guitar (Denmark) wrote me in response to trapezoidal neck design:
"I read with great interest your post on the trapezoidal neck and its square aluminium tube truss rod. I see one potential problem: the thermal expansion of aluminium is a lot greater than that of wood. Aren't you concerned that the truss rod will come loose or split the neck if the guitar is subject to changing temperatures?"The thermal expansion coefficient for aluminium at 25 °C is 23.1 µm·m−1·K−1 (according to Wikipedia) - meaning that one meter of aluminium expands 23.1 millionth of a meter each time the temperature increases one degree. For an aluminium guitar one meter long, a ten degree increase in temperature (Celsius or Fahrenheit) will mean that it becomes 0.23 millimeters longer (that's about a hundredth of an inch). Not a lot, if my calculations are correct, but certainly enough to make a difference, at least in tuning.
"One of my major concerns is that the neck (or indeed the whole guitar) will bow if there's more wood on one side of the aluminium than the other. Your design looks like it has about the same amount of wood on all sides of the truss rod, so that might keep it from bowing. A neck built from aluminium only with a wooden fingerboard, on the other hand, might exhibit severe bowing when the temperature increases.
"It's all just speculation on my part...I am about to build a guitar of wood and aluminium — and have thought a lot of the issue of different thermal expansion coefficients. If you have any opinions on the matter, it'd be interesting to hear. Perhaps as a new article on your blog."
For clarity and brevity, I condensed two of Alex's emails into the quote above. It's a great question.
This is where theory meets example.
Goran's walnut Starfish has two 3/8" x 1/2" side by side aircraft grade aluminum stabilizing bars the full length of the neck, epoxied in place. That instrument also has a stacked laminate neck set into body.
Starfish was built in 1993, and has been played in conditions from 45F to 102F throughout North America and Scandinavia with no problems, adjustments or changes...almost 15 years of service. I could reliably expect to pull it out of the case after six months and find it still in tune.
PS: Please feel free to email Goran directly if you have any questions about his experiences with Starfish.
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