One influential factor that may not at first appear obvious is the availability of suitable (and suitably inexpensive) manufacturing technology. As new manufacturing technology becomes available in any field, it is generally first exploited to perform analogs of more traditional manufacturing processes. Such has been the case with Computer Numerical Control (CNC) technology, which has been used effectively as a substitute for more manual processes in both large and small guitar shops. But as more folks become more familiar with a new technology, the tendency is to move beyond the mere substitution of the new technology for an older one and to begin to fully exploit its unique advantages. This process feeds back into and affects the design of the manufactured item.

Australian guitar manufacturer Cole Clark Guitars has made efforts to fully exploit their CNC routing facilities, and these efforts include substantial design changes to the instrument itself. The company was started by Bradley Clark who, with eleven years of guitar manufacturing experience at Maton, Australia's largest guitar manufacturer, and a bagful of new ideas, was able to attract financing for this new venture. Having considerable experience with three-axis CNC routers and conventional guitar construction, Brad had developed some ideas on a totally new approach to acoustic guitar design and manufacture. His basic approach was to leverage CNC accuracy toward the development of a manufacturing and assembly process that would significantly reduce assembly time without compromising quality. Previous experience in an automated manufacturing environment indicated that the most basic dreadnought could be produced with five to six labor hours over the course of a three to six-week period. His goal was to reduce the assembly time to just a few days.

At first Cole Clark assembled an eight person staff and acquired a SCM 120 three-axis CNC machine with a ten tool magazine. To get started, the company began producing solid body electrics and lap steels, and also started the design effort for a steel string acoustic. In addition to the goal of reducing manufacturing time and labor, goals for the acoustic also included using CNC technology to enhance tone, balance, and volume; achieving a level of playability equal to guitars at the higher end of the market; and producing instruments robust enough to stand up to working musicians.

From the manufacturing perspective, all the above needed to be delivered at price points that would afford the company the chance to acquire enough market share to endure viability. Prototypes of the acoustic guitar were built and further development took place with the aid of the new five axis CNC machine, a Cosmic 6200. Photo 1 gives some idea of the size of the machine. The design of the Cole Clark Guitar is radical in several aspects. Photo 2 shows a machined neck blank, which features a jointed peghead and a Spanish heel. Slots are machined into the heel for the sides, similar to the system used in classical guitars. The neck is the platform around which the guitar is constructed. The CNC machinery allows the production of components with a very high level of consistency. The allows indexing the soundboard to the neck using its main braces, the ends of which are pocketed into the Spanish heel. The braces are let in shallow pockets on the soundboard to precisely position them. Thus neck alignment and action are guaranteed. Photos 3, 4, and 5 show the neck in detail. You can see the slots on the top of the heel in Photo 4 that will accept the ends of the main top braces. The two round holes are indexing holes used to position the neck on its jigs.

The bracing pattern is designed to provide an optimum strength-to-weight ratio. Photo 6 shows the soundboard with the braces glued on. They are let into the shallow pockets on a thicker-than-standard top as shown in Photo 7, facilitating high levels of consistency in brace location and ease of assembly. The underside of the top is graduated to provide the most responsive top plate without compromising strength. Note the absence of finger braces. Graduation parameters were arrived at through extensive testing. Tone, balance, and volume all benefit from graduation. The graduated tops are thicker around the braces. In this way there is less wood where required: both strength and flexibility are controlled. Carving soundboards in this way optimizes weight and possible acoustic efficiency. It also allows the routing of aspects, such a trending for the braces, which aid assembly.

The braces are longer than the X braces of the Martin tradition, and there are distinct possible advantages in running braces more with the grain. The more the braces run across the grain, the more the soundboard will move up and down with changes in humidity. The more the braces are aligned with the grain, the less the differential of expansion, and therefore the least movement with humidity.

The point of the manufacturing system is not necessarily the current top's unique bracing. The system did however allow the rapid development of the current unique bracing. Similarly the manufacturing system could provide for equal-thickness sounboards. Again, the point of the system in not necessarily graduated tops. Few at Cole Clark question, however, that substantial gains have been made by using the internally carved and graduated tops. Much has certainly been learned from the practice.

Photos 8 and 9 show that, as with the top, the back braces are let in to shallow pockets and the back is also graduated. Graduation of the back marginally reduces weight and makes a small but significantly positive contribution to the guitar's sound. Note the absence of a center seam graft. It takes minutes to fit a back. There is no adjusting of the sides, or the applying, leveling, or shaping of linings to match the back's curvature. It is simple to vary the weight of the back. Generally the weight is about a third less than that of its conventional counterpart.

Photo 10 shows the groove in the top plate to receive the sides. On assembly, the braced top is attached to the neck on a fixture. Accuracy in locating the top if facilitated by the fixture and the housing of the main braces in the heel. Photo 11 shows how the top and main braces fit into the neck heel. The alignment fixture is not shown.

The top and back contain 3D grooves or shelf routings, which match the curved geometry of the fitment to the sides. There are no linings. Linings are time consuming to fit and align, and add weight and adhesive. Since the neck is fitted to the top and the sides in turn to the neck and top, linings could easily be applied, face to sides, either as continuous linings or as individual strengthening pieces, consistent with some traditional European-built instruments.

The current practice of not using linings, however, has resulted in instruments at least as robust as higher-end conventional guitars.

After the top is fitted to the neck, the bent sides are fitted into grooves in the top and heel. A modified fixture is used to accommodate models with a cutaway. The sides are then reinforced and, where a top transducer is required, this is fixed into place in a machined recess (Photo 12). The back is then installed by flipping the fixture and locating the sides in the groove on the back.

Models that require binding are routed on a fixture and fitted with wood binding approximately 0.7mm thick.

Although jogs to assist in the binding operation are planned, binding is currently performed in a relatively traditional manner. Cole Clark has an entry level instrument in the production line, the FL1, which is unbound. On this instrument the plate overhangs are simply trimmed off flush with the sides.

At this point in construction the guitars are complete, minus fingerboards and bridges. The same location holds that were used to align the components to the manufacturing jigs and which were used to align the instrument to the assembly jigs are used to align the fingerboard and bridge to the guitar. Fingerboard and bridge are fitted, and then the guitar is finished. Since components are very accurately produced and fit together precisely, very little hand adjustment is necessary. The integrity of fitment seems to improve acoustic performance as it does manufacturing efficiency. There are no expensive or difficult-to-produce body jigs used in the manufacturing and assembly processes. Jigs are designed and drawn at the same time as the components they hold, and are manufactured on the same CNC machine that is used to rout the guitar parts.

Two general classes of jigs are used - CNC hold-down jigs and assembly jigs. Assembly jigs have some similarity with traditional Spanish assembly jigging. Most aspects are relatively simple, but some jigging is proprietary and some patented. There is a facility to replicate all stages of jigging. Jigs are made to produce jigs. There is an emphasis on the quick change of jigs and therefore models. As it currently stands, it only takes minutes to change from the production of acoustic to electric guitars. This further facilitated by the fact that no tool reset is needed on the CNC machine when changing to production of a different instrument.

All components are presented to the CNC router as rectangular stock and so this stock is relatively easily produced and handled. This detail also adds to the efficiency of the manufacturing operation.

Software used in the process includes various standard off-the-shelf CAD and CAM software packages, and a good deal of proprietary software as well. Drawings are generally made using Rhino CAD software, the drawing facilities of the EdgeCAM software package (which is also used to run the machine), or AutoCAD.

Guitars can be assembled within 24 hours. This fast potential assembly time provides advantages for production, and it also provides advantages during development. Since design iteration is mostly a matter of programming, new prototype instruments with varying parameters can be manufactured, assembled, and then tested and compared in less than two days.

Three models of the acoustic are currently in production with a new design in the pipeline. The models differ primarily on materials and in level of ornamentation. Cole Clark uses a number of native Australian wood species as well as more traditional lutherie wood species. See timbers page ...

Ultimately it is hoped the manufacturing system will have the capacity to deliver customer-selected parameters regarding sound. Meanwhile the company's desire to provide their customers with value for money and affordable solid-wood resonance. Ease of assembly of components and the use of CNC technology in providing this outcome in some form is inevitable. The process will to some degree demystify instrument making and provide better understanding of the components of sound production, which is expected to lead Cole Clark to new patents. A new model acoustic guitar incorporating some of those developments is currently in the design phase.

Reference: American Lutherie - The Quarterly Journal of the Guild of American Luthiers

Issue Number 83 / Fall 2005