Monday, 9 November 2015

Creating a guitar fingerboard sanding block

After deciding that drilling holes into a wooden fingerboard was a non-starter of an idea, and that casting the frets as part of a resin neck (either with fret-wire added to the mould or casting the frets directly from resin) was no good, there seemed to be only one option left:

To cast the fingerboard and then add the fret wires back in afterwards.

To try this idea out, we need a fingerboard blank without the fret wires embedded in it. Unfortunately, fingerboard blanks are either completely blank (and rectangular cut) pieces of hardwood (into which you cut the fret slots and sand/shape the sides) or entire fingerboards are provided with the fret wires already embedded. Try as we might, we can't find a fingerboard cut to size, with slots, but no fret wire.


Quite often you can buy a fingerboard blank, or a guitar neck with fitted fingerboard. Very rarely can you get hold of a pre-cut and fitted fingerboard. But finding a fingerboard without frets fitted is pretty much impossible.


There are plenty of places to buy entire guitar necks - but removing the fingerboards can be tricky. We got lucky with our Gear4Music guitar neck - a bit of heat and it came straight off (although not quite as straight-forward nor injury-free as it sounds). We tried removing a fingerboard from an old Marlin guitar and it refused to budge. Even the one that came with our kit couldn't be removed easily.


Even after copious amounds of heat, our knife blade wouldn't slip between the fingerboard and the neck, and it looks more like we're actually cutting into the wood of the fingerboard. That's some tough glue they use on such a cheap, chinese guitar clone!

Even when we've managed to completely remove a fingerboard without destroying it (or warping it beyond recognition during the removal process) removing the fret wires from an existing fingerboard has always proved more difficult than we expected - the only way we've so far managed to remove frets from a fingerboard is by bending the wood back to encourage the wire to pop out (though sometimes - and especially if the fret wire has been epoxy-glued into place - the fingerboard can splinter and crack before the wire comes free.)

So we've decided that working with existing fingerboard is just too fiddly - we'll have to have a go at making a blank fingerboard ourselves. Getting the fret distances right should be relatively easy, thanks to the laser cutter and StewMac's fretboard calculator. But before we cut any wood, we're going to have to shape it into a rounded shape.

Most electric guitar fingerboards have a "radius".


What we need is a concave sanding block - something to run along the fingerboard blank to create a slightly domed surface. There are numerous articles online about creating a sanding block with a specific radius, but almost all involve marking blocks of wood, planes, spoke-shaves, rasp files and/or heavy duty belt sanders.

Of course, with access to a laser cutter, it only made sense to use that to create our curved block.


Our first idea, using 6mm dowelling rods and laser-cut mdf was a bit tricky to implement. So Steve suggested slotted struts. A far better idea!


Using the same princple as the "living hinge" we part-cut some slots into another piece of mdf, to create a curved surface to accept the sandpaper. Even with the cuts in the curved section, it required a lot of force to hold it in place against the curve of the sanding block


After hunting around for something with exactly a 13.5" radius curved surface to strap the block onto (to act as a clamp while the glue dries) Jake came up with the ideal solution - a "negative" of the sanding block.


Now we've something to clamp against the underside of our concave sanding block, it's just a case of applying plenty of PVA wood glue and clamping the whole lot together.


The bench vice was perfect for clamping the whole assembly for about 40 minutes while the PVA wood glue dried.

This creates one continuous strip of a curved surface, with a 13.5" radius along the entire length of the block, secured every centimetre or so, to ensure a continuous, consistently curved surface - just the thing for making a curved, sanded surface!


It was only after completing our first sanding block and trying it along our guitar neck, we realised our first mistake:


We settled on a 13.5" radius because I have a Yamaha Pacifica which I think plays particularly well. Since no-one else had any other preference, we went with that. While it's quite likely that the radius on the fingerboard of our existing guitar neck is not exactly 13.5" we seem to be quite a way off the mark here.

It was only after double-checking the Inkscape design files, we realised the pattern had been drawn with a circle with a 13.5" diameter - making the radius half of what we thought it was, 6.75"

In the 50s it was common to find guitars with rounder, smaller-radiused necks. The rounder neck makes them easier to play chords with (and, consequently, more difficult to play leads and single-note licks). Early electric guitars were mainly accompanying instruments, rather than instruments in their own right, so a lot of players preferred the rounder necks, to make chord playing easier.

It was only really when lead guitar playing became popular in the early 60s onwards that players started to look for flatter, larger radius guitar necks. Even the most "classic" of electric guitars rarely had a radius much smaller than about 7". It turns out we'd created a perfectly curved sanding block that was no use for modern guitar playing!

Luckily, having perfected the technique of making the sanding block, relatively quickly and easily, it was just a matter of modifying the design files and laser-cutting some more mdf. The second version looked like a much closer fit:



With our sanding block built, the next job is going to be making the fingrboard blank.
Files for creating a 13.5" radius sanding block: