Posted on September 2, 2022September 2, 2022 by Dale Phillips 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. 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.