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A Method for the Design of the Guitar Body Outline

A Method for the Design of the Guitar Body Outline

by R.M. Mottola

Originally published in American Lutherie #97, 2009



See also,
Parametric Models of Guitar Cutaways by R.M. Mottola
A Method For the Design Of the Guitar Body Outline Part 3: Compound Radius Curves by R.M. Mottola



One of the most tedious and time consuming aspects of designing a new guitar for me is the process of designing the body outline. The body outlines of my early instruments were the results of many hours of labor, usually over the course of many weeks. This process was so time consuming that I would often forgo it entirely, opting to reuse an existing body outline as is, or scaling up a guitar outline for use in an acoustic bass guitar. But over the years I’ve settled into a method for guitar body outline design which is far less tedious and consumes far less time than did my original efforts. This method involves the use of a standard model of the guitar outline. Use of this standard model helps to make the process of developing an outline more standard as well, and this in turn has resulted in the development of techniques which save time and frustration.

In this article I will be outlining the model and discussing some common guitar body types in the context of this model. In talking about the design method which makes use of the model, I’ll try to touch on some of the generic qualities of guitar body outlines and how they can be quantified in terms of the model. Finally, some of the tools and techniques of the method will be detailed. Please note that what I am discussing here is only the mechanical aspects of a body design. Issues of acoustics or ergonomics are not covered. Also note that this method works equally well with either pencil and paper or CAD drawing tools, although there are some differences in how these tools are used.

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Parametric Models of Guitar Cutaways

Parametric Models of Guitar Cutaways

by R.M. Mottola

Originally published in American Lutherie #99, 2009



See also,
A Method for the Design of the Guitar Body Outline by R.M. Mottola
A Method For the Design Of the Guitar Body Outline Part 3: Compound Radius Curves by R.M. Mottola



In the article entitled “A Method for the Design of the Guitar Body Outline” in AL#97, I introduced the concept of parametric models for the design of the guitar body outline. That article addressed symmetrical body outlines only. In this article I want to consider parametric models for the body cutaway. Taken together the two articles demonstrate a complete method for the design of typical guitar body outlines.

Although it was possible to devise a simple parametric model for the design of the symmetrical guitar body outline that was adequate for most of the “standard” guitar body outline types, things are a bit more complicated where the cutaway is concerned. The basic problem is that, except in the most basic designations, cutaway styles have not yet settled out into a small number of distinct types. Rather than pursue a model that would accommodate all existing cutaway designs, I chose instead to derive basic models for the two primary cutaway types, leaving enough configurability to insure that most existing cutaway outlines could at least be approximated.

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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.

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A Method For the Design Of the Guitar Body Outline Part 3: Compound Radius Curves

A Method For the Design Of the Guitar Body Outline Part 3: Compound Radius Curves

by R.M. Mottola

Originally published in American Lutherie #103, 2010



See also,
A Method for the Design of the Guitar Body Outline by R.M. Mottola
Parametric Models of Guitar Cutaways by R.M. Mottola



The article “A Method for the Design of the Guitar Body Outline” in AL#97 presented a model for drawing guitar body outline halves based on five circular arcs and three straight line segments, as shown in Fig. 1. Here I will present an enhancement to that model. As the original article pointed out, the five-arc model can be used to draw most but not all guitar body outlines. So it was probably inevitable that the first feedback I received following the publication of that article was from someone trying to draw an outline for one of the instruments for which this model is not ideally suited. There are a couple of common instruments that have outlines which cannot be drawn using this simple five-arc, three-straight-line-segment model. These instruments, the OM and the Maccaferri-style guitars, have a “dropped hips” look to the lower bout that cannot be approximated by a single circular arc (Fig. 2).

Fortunately, the lower bouts of these guitars can be accurately drawn with a simple enhancement to the model. The enhancement replaces the single-arc lower bout curve with a compound-radius curve. A compound-radius curve is composed of a series of circular arcs, each tangent to the one succeeding it. Although all manner of complex curves can be built up in this fashion, for the purpose of enhancing the simple guitar body outline model, we really only need to introduce compound-radius curves of two radii.

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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.

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Quickie Sander Fence

Quickie Sander Fence

by John Calkin

Published online by Guild of American Luthiers, July 2022

 

Every lutherie shop has jigs hanging around. Often, lots of them. Every sort of stringed instrument is easier and faster to build using good jigs. If you decide that you'd like to build all of the instrument types commonly played in America you will accumulate a serious number of jigs.

These days just about all of the most useful jigs can be purchased from a variety of dealers. They are very pretty and often better-made and more useful than a jig we would bother to make in our own shop. Well, prettier, anyhow. If you have entered lutherie in the last fifteen years you may have grown tired of old-timers complaining about this, as if making all of your own jigs was a right of passage that should never be skipped. "In my day we couldn't buy a guitar jig of any kind anywhere! We were lucky to find a book with pictures of guitars, let alone instructions to make them. Huff!"

Well, sometimes we need a jig or fixture (what's the difference, anyhow?) that isn't instrument-specific, but machine-specific. I have vague memories of making a right-angle fence for my 6×48 belt sander. I still have the same sander, so when I rediscovered the jig---er, fixture---a few weeks ago I was glad to see it. But as soon as I turned my back, darn if it didn't go into hiding again. I have bumped around my little shop a number of times searching for it but to no avail.

So, today I made a new one. I remember having to shim the old one to get it square. The new one came out dead on the money. I'll claim that forty years of experience was responsible for that, rather than blind luck. Old-farts in the game are entitled to that. Belt sanders vary enough in design that I won't bother listing any dimensions. I have included enough photos to suggest the jist of it. Anyway, you'll probably want the fence to be longer, or taller, or shaped like an animal for all I know.

I sat it on a thin spacer to clear the belt, and it remained there nicely while I put on the clamps. Use the smallest clamps that will work in order not to bump them against the underside edge of the belt. Good luck.

All photos by John Calkin.
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Meet the Merchant: Jay Hostetler

Meet the Merchant: Jay Hostetler

by Jay Hargreaves

Originally published in American Lutherie #91, 2007



Founded in 1968 by C.E. “Kix” Stewart and Bill MacDonald, Stewart-MacDonald started off selling banjo parts and being innovative. Almost forty years later, Stew-Mac is are still being innovative, and still selling banjo parts. But now they also offer hundreds of tools, parts, and materials for all kinds of luthiers.


Jay, where were you raised?

On a farm outside Athens, Ohio. I spent a lot of time in the woods. My dad’s a wood sculptor, and taught at Ohio University, a small college in Athens. So I grew up around artists and wood and nature. It’s a nice setting.

In high school, about 1973, I started working in a furniture place. I enjoyed that, and I started making furniture. After high school I was going to go to the School for American Craftsmen in Rochester, New York. But they had a waiting list, and while I was waiting I started working at StewMac doing woodworking. At that time, all we did was banjos, mainly banjo kits. That was about 1977, so they were still riding the banjo wave of Deliverance.

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