Posted on June 6, 2024May 23, 2025 by Dale Phillips Questions: Jig for Oval Rosettes Questions: Jig for Oval Rosettes by R.M. Mottola Originally published in American Lutherie #97, 2009 Greg Pacetti of Fairbanks, Alaska asks: I’m in pursuit of some kind of jig for oval rosettes. The Questions column editor responds: Probably the single best source of info on cutting oval rosette channels appeared in the American Lutherie article “Making Oval Mandolin Rosettes” by Jonathon Peterson, et al. (AL#41 p. 34, BRBAL4 p. 140). In it, seven builders describe their methods. ◆
Posted on June 6, 2024May 27, 2025 by Dale Phillips Questions: 17″ Scale Length String Questions: 17" Scale Length String by R.M. Mottola Originally published in American Lutherie #87, 2006 Rob E. of Lexington, MA asks: Does anyone know of a string that can be put on a 17" scale length instrument, with an after length to the tailpiece of about 6", that is strong enough to reach a mandolin E tuning without breaking? “Questions” editor R.M. Mottola answers: A string with a small enough diameter to be tuned to this pitch at this scale length will have a breaking tension that is too close to its static tension to be of much practical use. When specifying the scale length for a new type of instrument, use a length similar to that used by existing designs with the same pitch range. For high-pitched instruments with long scales (such as the instrument in question) the issue is finding a string with high enough breaking tension to be useful. Unfortunately there are no simple solutions short of having strings custom-made of high-tensile-strength materials. For low-pitched instruments with short scale lengths the issues are tone and, for fretted instruments, intonation. Short, fat bass strings don’t behave much like ideal strings and their partials tend to skew way sharp as they are further shortened by fretting. There is a mathematical relationship among scale length, pitch, tension, and mass per unit length of a vibrating string. Download the paper entitled “Catalog Supplement / String Tension Specifications” from the D’Addario website. The paper (in PDF format) can be found at www.daddariostrings.com/Resources/JDCDAD/images/tension_chart.pdf. It contains comprehensive info on the string formulae as well as mass-per-unit-length (unit weight) data for every string D’Addario makes. Unfortunately, breaking strength data is not available in this paper as the issue of specifying the tension at which a real string will break is more complicated than it might appear. Tensile strength data is available from wire manufacturers but the best bet is to design high-pitched instruments using short enough scale lengths.
Posted on June 6, 2024May 23, 2025 by Dale Phillips Questions: Scale Length Questions: Scale Length by R.M. Mottola and Tim Olsen Originally published in American Lutherie #93, 2008 Byron from the Internet asks: Is there any way to determine the scale length of an instrument from a piece of the fingerboard? I have the fingerboard from an instrument that is currently being restored. The nut end had been trimmed, I think to accommodate some kind of odd nut. The Questions column editor responds: All inter-fret distances are related to scale length, so measuring, say, the distance between the 1st and 2nd fret and then looking that up on a fret scale chart will tell you the scale length. Or measure the distance between the 7th and 19th fret (assuming the instrument has a 19th fret of course) and multiply by three. The result will be within a few hundredths of the actual scale length, close enough to identify it. American Lutherie editor Tim Olsen responds: Imagine you put a capo on the 1st fret of a functional guitar. Measure from the 1st fret (now functioning as the nut) to the 13th (now functioning as the 12th), and double that to find the mathematical bridge point. If the fretboard is still on the guitar, you can find that point near the saddle and mark it. If the fretboard is not on the guitar, you can clamp it to something, like a 2×4, and mark the bridge point on that. Now you could easily find the nut point by measuring from the newly marked bridge point back to the 12th and doubling it. Confirm it by calculating the scale and checking the position of the individual frets. ◆
Posted on June 6, 2024May 23, 2025 by Dale Phillips Questions: Thickness Measuring Tool Questions: Thickness Measuring Tool by Tom Nelligan and R.M. Mottola Originally published in American Lutherie #92, 2007 Georges E. Vougioukalakis from Athens, Greece asks: In my experimentation and research on double-top guitar construction I find a need for an instrument that can measure the thickness of the outermost skin of the top on a fully assembled instrument without damaging the top. Does anyone know of such a tool? I remember a citation of an instrument that was used to measure the thickness of the paint in autos. Tom Nelligan from Olympus NDT/Panametrics-NDT Products in Waltham, Massachusetts replies: Commercial ultrasonic thickness gauges of the sort made by my company (and our competitors) for measurement of industrial engineering materials like metals, plastics, and ceramics will not work on wood, because wood does not efficiently transmit sound waves at ultrasonic frequencies in the MHz range. Pulse/echo ultrasonic gauging is based on very precisely measuring the round-trip transit time of a short pulse of very high frequency sound waves through the test piece. But the high frequency/short wavelength wave front is scattered by the microstructure of the wood, so it is not possible to get the necessary clean echo from the inner wall. Become A Member to Continue Reading This Article This article is part of our premium web content offered to Guild members. To view this and other web articles, join the Guild of American Luthiers. Members also receive 4 annual issues of American Lutherie and get discounts on products. For details, visit the membership page. If you are already a member, login for access or contact us to setup your account.
Posted on June 6, 2024May 14, 2025 by Dale Phillips Another Method for Calculating the Area of a Plate Another Method for Calculating the Area of a Plate by R.M. Mottola Originally published in American Lutherie #70, 2002 and Big Red Book of American Lutherie Volume Six, 2013 There are a number of reasons to calculate the area of the plate of a stringed instrument. The area of a flat plate can be used to determine the volume of the instrument by simply multiplying the area by the depth. This value is useful in the design of electric guitars and basses to determine the weight of the body of the instrument before it is built. This info can aid in the design of an instrument that balances well when hanging from a strap or sitting on the leg. In the design of acoustic instruments, the volume can be used to calculate the nominal Helmholtz resonance of the soundbox, which may be useful in the tuning of the resonance characteristics of the instrument. The technique specified here will work for any arbitrary shape and is both simple and relatively quick. It is the essential algorithm of a CAD script I use, and is based on a computer graphics rasterization technique. Modified and simplified for use with pencil and paper, it yields a good enough approximation of the area of a plate for the purposes outlined above. Become A Member to Continue Reading This Article This article is part of our premium web content offered to Guild members. To view this and other web articles, join the Guild of American Luthiers. Members also receive 4 annual issues of American Lutherie and get discounts on products. For details, visit the membership page. If you are already a member, login for access or contact us to setup your account.
