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This is my homemade fret slot cutting jig made from some aluminium angle that used to form part of my old fish tank unit.
The base is a solid block of aluminium fastened to a chip-bard base. The blue clamp was found in a drawer in the garage and the rest is just a collection of nuts, bolts and bearings. The wing nuts allow adjustment to the work piece channel to ensure a snug fit of the fret board to be cut. The clamp provides extra security and ensures the fret board remains flat to the base whilst the slots are cut.
The four pillars of bearings allow the cutting saw to pass to and fro without deviating from the vertical plain and so ensure slots are cut perfectly vertical and of equal width throughout. The saw will cut down until its’ spine runs along the top row of bearings. These can be adjusted to control the minimum height of the saw and thus ensure all slots are cut to an equal and exact depth as required.
It’s a simple design but very effective – as is often the case.
As a matter of interest (just in case you were), the frets on a guitar – or the fingering position of any string instrument is determined by the instrument’s scale length. That is the distance between the nut at the top end of the strings and the bridge at the bottom. In other words, it’s the length of string that actually vibrates to give the sound.
When you hold a string down with your finger you are creating a new scale length which, as the tension remains constant, increases the pitch of the vibrating string. To calculate the exact position to match the increased pitch with the next note in the musical scale you divide the scale length by 17.817. This gives the exact position of the next fret/fingering position. The distance from the new fret to the bridge is the new scale length so you simply divide this new length by 17.817 again for the next fret and so on until you have as many frets as you require or you run out of fret board.