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Mechanical Compliance for Soundboard Optimization

Mechanical Compliance for Soundboard Optimization

by David Hurd

from his 2006 GAL Convention workshop

Originally published in American Lutherie #90, 2007



People say, “You’ve got to make fifty or a hundred guitars before you get it right.” That makes me crazy. I feel that if you can do the carpentry of putting an instrument together and have idea of what it should look like, you can get 80% or 90% of the way there in terms of top optimization with a mechanical compliance approach.

I build many sizes of guitars and ukuleles using different top woods. I have developed an easy method of testing the compliance of a top, that is, how far it flexes under a given force, with a simple fixture. Being able to measure and compare the compliance values has proved to be a very useful thing in optimizing these soundboards for the best sound and stability when I graduate the edges of the tops and carve the braces.

After building and measuring many instruments, I have developed a mathematical model that does a very good job of estimating what the target compliance measurements should be for a given instrument size and string tension. I have integrated the model into a spreadsheet which you can use by plugging in just a few simple measurements.

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Construction of the Colombian Tiple

Construction of the Colombian Tiple

by Anamaria Paredes Garcia and R.M. Mottola

Originally published in American Lutherie #90, 2007, Big Red Book of American Lutherie Volume Three, 2004



American Lutherie #82 featured an article and plan for the Colombian tiple by Bogotá luthier Alberto Paredes. This is a companion article to that one, featuring a detailed description of how the tiple is constructed in Sr. Paredes’ shop. The design of the tiple is heavily influenced by that of the classical guitar, but as it was not directly descended from the classical, this instrument has unique characteristics. With its multiple courses of steel strings, the construction of the tiple has to be able to withstand much higher static string tension than a classical guitar.

The top is cut from bookmatched spruce, nominally 3MM thick. The two halves are generally cut out on the bandsaw at the same time, as shown in Photo 1. The center seam edges are jointed, first on the jointer (Photo 2). Following machine jointing the top halves are finished up on the shooting board using a hand plane. Note that the halves are simply pressed by hand to hold them down on the board during shooting (Photo 3). Glue is applied to the center seam surfaces (Photo 4) which are then clamped using simple cauls to a flat, waxed gluing board (Photo 5). Once the glue is dry the squeeze-out is stripped off the back side of the top.

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The MacRostie Mandolin Deflection Jig

The MacRostie Mandolin Deflection Jig

by Don MacRostie

from his 2004 GAL Convention workshop

Originally published in American Lutherie #94, 2008



The mandolin world is small enough that if you’re even thinking about building one, you probably already know who Don MacRostie is. Don is an inventor, and he’s done more for Stewart-MacDonald than we will ever hear about. He’s been making Red Diamond mandolins for two decades now. At the 2004 GAL Convention Don discussed one of his research tools and told us how he applies it to his construction process to make the sound of his finished instruments more consistent and predictable.

— John Calkin


At the GAL Convention in 2001, Charles Fox floated the idea of teaching a mandolin building class at his American School of Lutherie. As a result, I taught a two week class, building A-style mandolins from scratch. The only thing we started with was thickly precarved oversize tops and backs. Everything else we made totally from scratch. It was a great experience.

Peggy Stuart, a student in the class, documented the experience in a series of American Lutherie articles (AL#75–AL#79). Tim Olsen asked me to demonstrate and explain the plate-deflection machine we used in the class at this convention, so that’s why we’re all here.

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Electric Guitar Setup

Electric Guitar Setup

by Erick Coleman and Elliot John-Conry

from their 2006 GAL Convention workshop

Originally published in American Lutherie #98, 2009



Guitar companies can only set up their guitars to a certain level and still be cost effective. So even a lot of brand new guitars are brought to our shop to be super set up.

Since Erick works for Stewart-MacDonald and we both work in Dan Erlewine’s shop, most of the tools and materials we’re going to mention today are available from Stew-Mac.

We do all the neck work on the neck jig. This jig simulates the guitar under string tension. If you simply remove the strings, set the guitar on your bench, tweak the truss rod until everything looks level, then proceed to level the frets, you may find that once it is strung again your leveling job has gone to hell. You haven’t accounted for the abnormalities that string tension usually puts in the neck, and neither have you accounted for the effects of gravity differences between the guitar lying flat on your bench and the guitar in playing position. So we not only use the jig to simulate string tension, we tilt the guitar into playing position before the jig is adjusted. We use about a 70° angle to simulate playing position, since few of the guitar players we know have a stomach flat enough to hold the guitar at a 90° angle to the planet.

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Total Flame Out: Retopping a Harp Guitar

Total Flame Out: Retopping a Harp Guitar

by Harry Fleishman

Originally published in American Lutherie #100, 2009



Falling in love causes people to do crazy things. It made me build a harp guitar using a piece of redwood that was so obviously problematic that I should have run from it. But I fell in love with it for its beauty. I should have been faithful to the wonderful straight-grained wood I’d had such success with. But no; I was blinded by its gorgeous curls. Like a C-street politician, I’m paying the price now.

Replacing the top on a complicated instrument is no picnic, I can tell you. The harp guitars I’ve made have no actual centerline and no points of symmetry. But once I made the decision to go forward with the retopping, I remembered a cool description of how Taylor Guitars does it. Bob Taylor has the good sense not to trash a guitar just because it doesn’t sound good. He also has the good sense not to sell a guitar that isn’t up to his standards. He also has a CNC machine and interchangeable parts for his guitars. Not I.

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This article is part of the Articles Online featured on our website for Guild members. To view this and other web articles, join the Guild of American Luthiers. Members also receive 3 annual issues of American Lutherie and get discounts on products. For details, visit the membership page.

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