In terms of process, there are really two types of activities involved in designing an acoustic guitar and making a drawing to build from. The first is simply a matter of translating some numbers into a drawing. The fingerboard is like that. Fret location, dot marker location, the divergence of the sides of the board, these are all described in just a few numbers. Drawing the fingerboard from these numbers though is time-consuming and can be tedious. The second type of design activity is highly iterative. Designing the body outline is a good example of this. It is the kind of thing where you continually refine your work until you've got it just the way you want it. This process can also be tedious, whether drawing on paper or using drawing software.
The "G" Thang guitar drawing tool is a program that takes a lot of the tedium out of acoustic guitar design. This tool provides complete body outline design as well as fingerboard layout. The latter includes fret location, dot marker location and the dimensions of a proportionally spaced nut.
Initial appearance: March 18, 2009
Last updated: August 22, 2019
In American Lutherie #97 I wrote an article about a simple model which can be used to design the outline of an acoustic guitar. The model consists of five circular arc and three straight line segments for each half of the body. Although quite simple, this model can be used to accurately draw most "standard" guitar body outline shapes as well as a lot of nonstandard ones. The article described how to use the model to draw guitar body outlines, on paper, or using CAD drawing tools. An even easier way to design guitar body outlines is to use "G" Thang software, which is available for Windows computers and can be downloaded for free here.
The process of designing a guitar body outline is an iterative one. You take a good guess at what you want the outline to look like, draw it, evaluate your drawing, and then make modifications to it. The process can be tedious when done using CAD drawing software and is even more so if paper and pencil are used.
Some number of years ago, with the aid of another engineer, I developed two interactive scripts for use with an off brand CAD software package that made the process of designing the outline of the acoustic guitar simpler and quicker, and made the process of designing and drawing a fingerboard a simple matter of filling in a form. Although originally intended only as demonstrations of CAD scripting tools, I used these scripts on and off during the intervening years, even though each use required me to re-learn how to use the off brand CAD software. I needed to generate a number of body outlines for the above mentioned American Lutherie article, and this provided the impetus to convert the CAD scripts to a stand alone program.
"G" Thang uses the five arc, three straight line segment model described above (or optionally a seven arc, three straight line segment model), and provides features so you can iteratively and interactively make changes to your body outline design. The software "knows" a lot about the proportions of guitar bodies, and provides guidelines and other helpful facilities to make it easy to design your own body outlines. "G" Thang also includes a number of standard guitar and ukulele body outlines, so you can start your own designs from one of these standards if that is the way you want to proceed. Once you are satisfied with your design, you can either export it to CAD or drawing software via a .dxf file, or you can simply read line segment locations right from the "G" Thang window for use in your paper and pencil drawings. The tool also provides complete fretboard layout, including fret locations and dot marker locations, and it also automatically draws a proportionally spaced nut for you. The tool is extremely popular and has been downloaded thousands of times.
"G" Thang runs on Windows machines that have screen resolution of at least 1024 x 768. The main window is quite large, and higher screen resolution settings are preferred. But it will run on systems with 1024 x 768 resolution if taskbar properties are adjusted. See the documentation with the program for more details on how to do this.
The program is available for free download and may be used with no restrictions save that it may not be redistributed. A note about viruses: This software is regularly scanned for viruses using Windows Defender. I receive occasional reports from folks about Norton antivirus software griping about the installer program. So far, such gripes have always been the result of one of the following: 1. the virus software was configured to be too sensitive and rejects all downloadable executables (reconfigure the virus software settings to something more sensible); 2. the virus software is emitting a false positive (these generally go away by themselves after a few days); 3. The person did not download the software from the LiutaioMottola.com site (only download it from the LiutaioMottola.com site).
Want to show your appreciation? If you use the tool to transcribe the body outline of a known instrument, please consider emailing me a copy of the resulting .gthang file. I will make all contributed .gthang files of standard instruments available here for download.
Download "G" Thang 0.7 installer (6.2 MB .exe)
The latest version of "G" Thang has a number of added features. The body outline snapshot feature is useful when designing an outline as a variation of an existing outline. It lets you see where you've been as you iteratively change the outline to your desired shape. Also included in this version is a facility for adding the coordinates of transcription points, which is useful when attempting to transcribe a body outline from an existing instrument or drawing.
By the way, I would highly recommend getting copies of American Lutherie #97, American Lutherie #99, and American Lutherie #103 and reading the articles on body outline design and cutaway design. These serve as good background documentation for using "G" Thang. Of course, all serious luthiers are members of the Guild of American Luthiers and get American Lutherie as a benefit of membership. You should too!
The "G" Thang guitar design software is unsupported, but I would be interested in hearing from anyone with bugs to report or features to suggest.