Constructional details for making a

Modular Electric Guitar

............................................................... with skeletal frets


picture of complete guitar

Several years ago, needing a project for a design course I was studying with The Open Universiy, and being a mechanical engineer, I came up with an idea for an electric guitar that was quite a bit different to the usual offerings at the time

The principal area of novelty was the fretboard (or rather the lack of one) coupled with a modular construction that gave greater playing accuracy and improved sustain

Please visit the following pages for the full story:


Concept

Drawing of Overall Concept

The concept of my skeletal guitar came from a combination of several factors.

The first was having had an active interest in electric guitars (both playing and constructing) over a course of 40+ years .

Secondly, being a design engineer having spent my whole career in precision mechanical engineering companies, manufacturing motor cycles, industrial comeras, hi-fi record players and T.V. studio equipment.

And, most importantly, having an uncontrollable urge to tinker with/improve any off-the-shelf gadgets that I might obtain, with an aim to making them perform to my own individual requirements.

When, one day, my thoughts turned to making an electric guitar, I put together a list of all the improvements on those currently available that I would want to incorporate into my new design. These were:

Drawing of Neck and Fret Concept

The thought of using a normal wooden neck did not appeal to me, so I considered the requirements of a guitar neck from first principles and came up with the idea of a 'fretboard-less' neck, that could be built using a metal tube as its backbone with fret plates attached (rather like a T.V. aerial.

Drawing of Concept Modules

Once this idea had occured, the next thought was "Why not let the neck backbone extend the full length of the guitar and mount all the hardware to it, as well".
This would then allow the guitar body to be a completely seperate item, attached to the neck but playing no part in the string-tensioned structure and, therefore, no part in the tonal quality of the overall sound.

The idea of a modular construction was then taken a stage further by designing the pickup and controls onto a scratchplate that was also self contained and easily removable from the other parts of the guitar.

More details and a fuller explanation of all the component parts of my guitar can be found on the following sections of this website.

I hope that you find the information interesting and, if you also feel the urge to replicate my ideas for your own construction efforts, and need any other details, please feel free to contact me.


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Neck

Neck construcion drawing

In order to achieve a suitable level of stiffness for the minimum weight, I decided to fabricate my own neck tube by bonding four aluminium alloy sections together: two channel sections (shown red and blue) and two angle sections (shown green and yellow).

This resulted in a slightly rectangular box section, having three wall thicknesses in the top and bottom walls and two wall thicknesses in the side walls, giving a higher stiffness in the important x-x plane compared to the lateral y-y plane.

A calculation of the expected tube bending, using typical string tension forces, gave a figure of approx 0.5 mm which is the same degree of neck relief aimed for in conventional wooden versions, fitted with adjustable steel truss rods.

The topmost outer wall of the fabrication was slotted to provide locations for the fret plates, which were made from 3mm thick aluminium alloy plate, individually sized and shaped to suit its position on the neck.
(see the 'fretting' page for details of the calculations involved in the shape/positioning of the fret plates).

After bonding the set of fret plates to the neck with a structural adhesive, the whole unit was up-ended onto a surface plate and the tops of the plates were carefully rubbed over sheets of emery paper in order to level them and achieve the required top curvature (camber).
(After a fair amount of use of the guitar, some fret wear was noticed and stainless steel capping strips were added to the tops of the fret plates).

Drawing of Hand Positioning on Neck

Initially, the ease of playing a guitar with a fretboard-less neck was a little bit in doubt, but I had been encouraged in my confidence by reading about Swedish guitarist Yngwie Malmsteen's signature model Stratocaster, that had a scalloped fingerboard to allow a higher degree of string-bending, which was a feature of his playing style

Also, when analysing the hand position that has to be adopted with my design, it is found that it corresponds exactly with the classically correct technique of a straight thumb pressed against the middle of the back of the neck with the palm of the hand well clear of the side.

In practise, I found that the difference in left-hand technique needed to play this skeletal form of neck, compared with a conventional one, was quite minimal and any effort in adjustment far outweighed by the tonal improvements.




(Hand positioning diagrams based on those from "How To Play the Guitar" by Roger Evans)


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Fretting

Although several fret spacing charts are readily available for various scale lengths of guitars, it is not too hard a job to work them out from first principles (especially with the help of a computer spreadsheet program, such as Microsoft Excel).

All that is needed to know is the 'magic number' 17.817, which is the factor that you divide the total string length by to obtain the distance between the zeroth fret (or nut) and first fret.

Taking away this distance from the original total length, and then dividing the remaining length by the same factor results in the distance between the first and second frets.
and so on and so on.........until you reach the last required fret spacing.

screenshot of fretting spreadsheet

If all the calculations have been carried out accurately, then the distance from the zeroth fret (or nut) to the twelfth fret should be exactly half the original scale length, i.e. giving an octave above the open string

Whilst getting the spreadsheet to work out the fret spacings, it is a relatively simple addition to also calculate the corresponding fret widths, as they increase from the nut towards the bridge
and, if you really get to grips with the maths, you can also calculate the change in camber radius (but I didn't bother, deciding to leave that to be done at the rubbing down on surface plate stage).

Here's a screenshot of the spreadsheet, which you can download by right-clicking the link and choosing "Save link/target as ...." and saving the xls file to your computer (the scale length and neck width parameters can obviously be changed to suit your own particular choices)

Download the Fret Calc spreadsheet

As well as the (fairly) obvious fact that the 12th fret is positioned at the exact half string length point, it is also interesting to note that the distance from the nut to the 5th and 7th frets works out at a quarter and a third respectively of the string length. Something that was known way back in the days of ancient Greece.

Read more about Pythagoras and his Vibrating Strings

As an historical note, when I made my guitar back in 1992, I never had the advantage of being able to use the Microsoft Excel program (did it even exist back then?), so all my calculations had to be done on a Sinclair Spectrum using my own humble attempt at coding a BASIC program

if you are interested, here is what it looked like.

Screenshot of Fretcalc program

If you want to view the full code then feel free to download the txt file in the same way as mentioned for the spreadsheet above.

Download the Fretcalc BASIC coding
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Headpiece and String Lock

Photo of Top of Headpiece

The headpiece was made out of 12mm plywood and shaped to match the angular profile of the body with its underside partially slotted to match the thinned-down end of the neck.

The headpiece was bonded and screwed to the neck, with their lower faces flush, and then filled and painted the same colour as the body.

As the neck incorporated a zeroth fret, there was no need for the usual nut found on most conventional guitars.
Instead, all that was needed was a string separation device.

BUT, after some playing of the guitar, involving use of the vibrato unit, I realized that I had a problem with loss of tuning. This, I realised, was the result of the changes in string tension between the separator and the machine heads not being equalised, due to excessive friction at the separator.

To overcome this problem I decided to remake the string separator and include six small nylon rollers where the strings divert across the headpiece to their individual machine heads. That helped to reduce the friction at that point, but to be ultra-sure I also decided to incorporate a string-lock function into the separator device.

This was achieved by fitting three small steel plates to the underside of the separator, which could each clamp a pair of strings. The clamping being effected by means of tightening dome-headed socket screws on the top of the separator.

Photo of bottom of Headpiece showing String Lock Key

This modification solved the tuning stability problem and I also incorporated a storing device for the hexagon key, that was used to loosen and tighten the clamps, on the underside of the headpiece, as the photo shows.


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Vibrato Unit

Drawing of Assembled Vibrato Unit

Having been a lead guitarist with several groups in the heydays of The Shadows and Duane Eddy, I considered it a necessity that my guitar included a vibrato unit instead of a simple bridge/tailpiece.
This decision, although easy to take, resulted in a considerable amount of design work and manufacturing time.

The problem comes about from the fact that the thro' neck idea leaves too little space above the neck tube in which to be able to fit a standard vibrato unit (or simple bridge, for that matter).
So I needed to turn everything upside down and mount the string anchor and bridge pieces above the strings, pointing downwards.

Drawing of Exploded Vibrato Unit

As the exploded drawing shows, the vibrato unit consisted of a U-shaped metal housing which had six slots on its upper face to which the individual string saddle blocks could be fixed and adjusted for intonation.
These saddle blocks each incorporated a slotted grub screw to allow the string heights to be accurately adjusted.

At the rear of the housing a square section bar with six holes was fitted to its underside to provide an anchor for the string ferrules.

Pivoting of the complete vibrato housing was achieved by two cone-pointed grub screws which sat into vee-bottomed holes in the pivot blocks that were mounted to the neck bracket, and the reaction force was provided by two tension springs fitted to a cross rod spanning the bottom legs of the housing.

The vibrato arm itself was a stainless steel rod, threaded at one end, that could be screwed into a mounting block on the inside wall of the main housing.
This block was slit part way through and a screw fitted to allow it to be tightened to give the required degree of rotational friction to the arm.


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Body

Drawing of Assembled Guitar Body

The body, whose function is no longer that of a structural element, is simply fastened to the underside of the neck and incorporates a set of short pillars for supporting the pickup controls scratch plate.

Being a separate item, the body can be attached/detached from the neck at any time without needing to de-tension the strings.

Drawing of Body Construction

The shape, size, material and finish can be chosen to satisfy any function or fashion.
I chose to make a very angular design that would be distinctive as well as easy to produce.

Again, in the interests of simplicity, the body was laminated from three pieces of plywood (2-10mm and 1-3mm thick) in order that the various pockets and cable apertures could be more easily made.

The pieces were then glued together and the edges sanded smooth before applying the final paint finish.

The set of 10mm dia wooden dowels were fitted into the pre-drilled holes in the upper surface, protruding the same height as the metal neck section, in order to provide support for the plastic scratch plate.

Lastly, a small plastic cover plate was made and fitted over the battery compartment aperture on the back of the body.


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Pickup and Circuitry

Picture of Sliding Pickup

One area of the design that I initially thought would be a problem was the mounting of the pickup(s), as the tubular neck of the guitar extends past the normal pickup positions and has insufficient space between its top face and the strings to fit a pickup into.

However, this drawback was soon turned into an advantage by my idea of inverting the pickup, within a sliding aluminium saddle, to allow the varying tone shades to be obtained more conveniently (and quickly) than the equivalent switching operation on conventional multi-pickup guitars.

Also, the saddle provided an extra degree of interference screening for the pickup as well as acting as a useful hand rest.

Drawing of Pickup Cirguitry

For extra refinement, I decided to fit a battery-operated pre-amplifier module in place of the normal passive tone circuitry as, apart from achieving greater tonal variation, it gives the ability to hear the guitar's output by headphones and not need the use of a practice amplifier.

A ready-made circuit board module (purchased from Maplins) was used to provide the active tone control and was powered by a 9v battery fitted into a compartment at the back of the guitar body..

A 2-pole 3-position slide switch was wired between the battery and the circuit board that allowed the selection of normal output from the pickup to reach the jack socket in the event of battery failure.

The bass, treble and volume controls were simply wired to the circuit board as shown in the diagram.
Note that the volume control is a twin-ganged potentiometer to allow for control of output volume in both amplified and normal modes.

Also, the output jack socket incorporates a switch which is useful to ensure battery disconnection when the guitar lead is removed (in case you forget to select the centre-off position on the slide switch).


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Contact me

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I hope that you have found the information on this website interesting and you are all fired up to have a go at making your own skeletal guitar.

If you would like any further information on my method of construction, then please feel free to contact me.

webmaster_burywsd@live.com


Links

For further information on (conventional) guitar contruction, I would recommend visiting the following websites:

General Guitar Making

Guitar Body Construction

Guitar Neck Construction

Guitar Construction Materials

Website created: November 2013 - Last updated: 25 August 2018
Author and webmaster: Peter Attwood

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