All components of this Red Special replica guitar that were required to be made on my CNC machine (body sections, neck, fretboard, upper oak insert, Bakelite nut, perspex pickguard set, aluminium switch frame and potentiometer/capacitor plate, aluminium roller bridge) or machined by third parties had to be reproduced in CAD and output as an STL file to be read into a CAM package (MeshCAM in my case) to create GCode toolpaths.
When the Red Special body shape 2D outlines were finalised, I moved on to working up 3D objects in TurboCAD. In a basic sense, this involves giving the 2D outlines depth and creating the cavities and rebates by adding and subtracting objects as required. In CAD/CAM jargon, simple 2D prismatic shapes with depth are referred to as “2.5D” objects (the guitar body sections in this case). Shapes such as the guitar neck with complex profiles in the Z axis (vertical directions) are genuine 3D objects. The four images in the gallery below are some renders of the final design from TurboCAD.
The Red Special Neck
Without going into too much detail on the CAD aspects of constructing a Red Special neck which are technical in nature and do not lend themselves to an interesting narrative, the process involves constructing a set of aligned 2D profiles then lofting a smooth transition between to achieve the 3D shape. In the case of the main part of the neck, this involves a progressive transition between a C shape at the headstock/nut region to a distinct U shape at the 11th fret which becomes a flattened U shape at the 14th fret. The second set of line drawings illustrate all the 2D profiles used to construct the headstock, main neck and tenon sections. The volute on the underside of the headstock is pre-formed in this illustration and consists of two sections; the rounded tip was created by sweeping the profile around a 180 degree arc. Note that the piece of mahogany Brian used to make the original Red Special neck was not thick enough to carve the whole neck from (probably only 1 1/4″ thick) so he had to build up the heel section at the body join by gluing another piece of wood on. The total thickness of my neck object in CAD is 35.2 mm so the shortfall would likely have been approximately 3.5 mm.
Red Special Headstock Shape – The Lightbulb Moment
Prompted by frequent discussion of the shape of Red Special replica guitars on enthusiast forums, in particular the headstock and the upper horn, I decided to examine the headstock design in early 2015. I measured the Red Special replica I owned at the time and found that the width of the headstock was exactly 3″ at the 1st and 6th string tuning heads, 2 1/2″ at the 2nd and 5th string tuning heads and 2″ at the 3rd and 4th string tuning heads. That got me wondering if they used simple geometric shapes (e.g. circles, ellipses) placed at simple rectangular coordinates in the design of the guitar and joined them up with line segments. I also realised (which is obvious with the benefit of hindsight) that the guitar was designed in imperial dimensions, not metric.
I stacked circles as shown in the schematic diagram and this fitted well the shape of the headstock ‘lozenge’. This was a lightbulb moment that lead me to carry out similar shape fitting exercises on the guitar body’s external and internal structure. I estimate that the lower return curve follows a 1 1/4″ diameter circle, because seems to yield the best fit. These are placed 1″ above the back of the nut to give this profile. The bottom of the 3″ circle is 1 1/8″ above the back of the nut. After examining The Red Special headstock shape and finding that it fitted circles with integer multiples and simple fractions of imperial measurements, I carried out a similar shape-fitting exercise on the Red Special guitar body with the assumption that Brian and Harold constructed this using a similar philosophy.
The Red Special Body
An important precursor to working up the Red Special body design in CAD is understanding the relatively complicated internal cavity structure of the guitar. Brian has stated that his goal was for the guitar to hold as much air as possible to allow it to interact with the amplified signal and feed back in a controllable way. He removed large proportion of the core softwood from the original blockboard using a wood chisel to form the acoustic cavity on the left/bass side of the guitar and a control cavity on the right/treble side of the guitar.
Although it is relatively well known that the Red Special construction uses oak and blockboard, X-ray images were taken in 2003 at St Bartholomew’s Hospital in London to allow its internal structure to be accurately determined for the Guyton authorised replicas. Presumably this was necessary because either Brian and Harold did not make detailed plans of the internal chambers, or that the end result differed significantly from the original design sketches due to cutting errors or ‘in field’ design changes which were not then reflected on the plans.
I therefore had to study the X-ray images and work up design sketches in the same manner as with the visible parts of the guitar body. The attached images illustrate the X-rays with construction lines drawn over them to form the cavities for the upper and lower sections and the design sketches I worked up from them. Note that the main body X-ray image is a montage of separate images that are pieced together. As a result, the features do not align well with the outline of the guitar and some educated guesswork was required on the position and size of the construction objects.
The Red Special Pickguard
Moving forward to early 2016, after the shape fitting investigations on the Red Special headstock, I carried out an analogous study on the pickguard. It appears that the pickguard outer edge tracks the body shape with a gap of 1/2″ (12.7 mm) and, as with the headstock and guitar body, circles with regular imperial diameters were used to construct the curves and were joined up with either line segments or ellipse segments using a draughtsman’s French curve set. The sketch in the gallery below illustrates only the construction objects placed at the nearest 1/8″ locus as specified in the list below and labelled. The pickguard shape in the small horn region does not exactly fit the regular ‘theoretical’ shape I proposed and line segment L2 joining the tip to the cutaway curve is noticeably curved. Is it because the tip region was damaged during cutting and Brian had to slightly reprofile this area to smooth out the cutting error? Or was it designed like this from the outset?
Aluminium Sheet Parts
I spent a considerable amount of time working up and refining the design for the intricate aluminium switch frame and potentiometer/capacitor mounting plate. I bought a set of vintage Jeanrenaud DPDT parallel slide switches from French electronics enthusiast and Deacy amp expert, Manuel Angelini which allowed me to design the electronics system to match the size and shape of the original Red Special. The potentiometer and capacitor mounting plate required a degree of educated guesswork and at least four design revisions to get it anywhere near the same as the original due to the lack of revealing pictures on this piece.
The Red Special Hardware (Tremolo Block and Roller Bridge)
Although I was able to obtain authentic replica Red Special hardware, as an academic exercise to improve my CAD skills (part of the project philosophy), I worked up 3D CAD designs based on the intricate aluminium roller bridge, mild steel tremolo tail piece and knife edge fitted to the Guyton Brian May Red Special replicas. You might find it instructive to review the design drawings that Greg Fryer has published on his website: https://fryerguitars.wordpress.com/red-special-scratchplate-and-hardware/
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