Fret Cutting Jig

[Malc2098]

I believe there are some very knowledgeable guitarists on this forum and some members may also have notable luthiering experience, but I have noted that non luthier and non musicians have found interest in my posts over the past year and I hope they find this thread of interest, too.

The frets are those shiny things along the neck of the guitar, the ukulele and other fretted instruments. And like anything on this forum that is made of wood, we need to know the measurements of any piece of wood that we are going to cut. The fretboard on the neck of instruments has frets most of the way along, until the gaps get too small for our fingers to press a string down between it and the next one, and you may have noticed that the gaps reduce the further towards the body of the instrument they go. And we luthiers have to know how to measure where all the frets go and need to make a cut to receive the frets.

This next piece, I've nicked off the interweb, and hopefully properly referenced, because it is far better at explaining the formula for calculating those gaps than I can.

The guitar produces very sophisticated music by producing different sound frequencies. Guitars designers/builders are called luthiers.

Stretched tightly between two points, a string when plucked, makes a specific tonal pitch. Pythagoras discovered that if the length of this string were to be cut in half, the pitch made would be equal in tone but at twice the frequency; an octave. The length of the string, tension, and its gauge (thickness) determine the pitch. On a guitar, the string length is controlled by the placement of frets on the neck.

Pleasant to the Western ear, the guitar neck is designed on a 12-pitch chromatic scale based on his principle. The 12th fret is the octave of that string. A formula, developed by Vincenzo Galilei in the 16th Century, mathematically determined the calculation of the distance between the tones initially uncovered by Pythagoras.

There are several different scale lengths on various guitars; determined by the instrument’s designer, the player’s personal preferences, gauge of the strings and length of the neck. Divide any scale’s open string length by 17.817, and the result is the distance from the front edge of the nut to the first fret. For several centuries, this number was rounded to 18 and referred to as the “rule of 18.”

For example, a typical guitar scale length (Fender Telecaster) is 25.5 inches (648 mm). The 25.5”scale length, divided by 17.817 is 1.4312173” (36.482011mm), rounded down to 1.431” (36.48mm). This is the placement for the first fret; the second note in the chromatic scale (the first note being the open string). A digital fret calculator is available on the Stewart-MacDonald website.

Formula for Calculating Fret Spacing: * Dn = [(L – Dn-1) ÷ 17.817] + Dn-1
Calculating the formula down the remaining scale length one locates the positions of the remaining frets on down the neck. As the string gets shorter, the distance between frets shrinks proportionately. The shorter scale length creates a warmer tone. Check out different brands and models to see for yourself.

Interesting Fact: An instrument’s timbre results from the unique tones created by varying scale lengths, tone woods, electronic pickups, guitar body sizes, etc. The variety of sounds emitting from guitars is virtually unlimited. The face of a guitar is the soundboard. Harder woods in an acoustic guitar’s soundboard make for brighter notes with less sustain. Softer woods (like spruce) make warmer tones with more sustain.


Reference:
National STEM Guitar Building Project: *http://www.guitarbuilding.org
Mathematics, Music, and the Guitar, David Hornbeck, http://jwilson.coe.uga.edu/EMAT6450/Cla ... /Hornbeck/ Math,%20Music,%20&%20Guitar.pdf

So, instead of marking on my forthcoming guitar and ukulele necks and then trying to cut straight cuts across to receive the frets, I'm about to make a fret cutting jig with templates for different scale lengths.

Photos tomorrow!

 

[novocaine]

An interesting idea. Look forward to seeing what you have (i noticed the laser cut templates so i can guess a bit of it)

 

[Cncpaul]

Malcomb

I have a piece of software that enables me to machine fretwork, if you give me some details of what you need
I can send you a cad drawing to set out your frets or any other help you might need.

Here is a brief description of how it works

​
The Gadget works with my CNC that lays out a chromatic fretted finger board. It is intended for guitar but it will work for anything that needs chromatic frets from mandolin or ukulele to and electric bass guitar. (of course you can delete the extra frets for dulcimers or other diatonic instruments).

How it works/What it does:

The fret and board layout is defined parametrically using the scale length(s) and number of frets. It supports standard/single scale or fan/multi scale fret layouts.

The board outline may be based either on the width of the strings at the nut and saddle, or set by specifying the width of the fret board at the nut and 12th fret. Options allow for a zero fret or cut line at the nut.

The gadget then generates the 2D drawing/vectors of the fret board outline, the frets, and slots if selected. Running in Aspire, the gadget also generates a 3D component for carving a radius either flat (no radius), single simple radius or a compound radius. The 2D vectors and 3D model provide design pieces needed to create the tool paths for carving a complete radiused fretboard.

 

[AndyP]

I’m one of those you neither plays, nor has any intention of making, a guitar. I do find it fascinating though. Thanks for sharing.

So making a violin would be a lot easier then

 

[Malc2098]

Paul, wow! What have I started here.

Your post got me thinking, thinking hard. What do I want from my hobby, and this project? I think that's part of the answer. I am retired, existing on a pension and this is my hobby. I get satisfaction from it; from solving problems and having an outcome that I can be proud of and learning lessons on the way.

In a way, I am not much different from MikeG and others on this forum, in that I like working with wood, feeling it, fashioning it, feeling it change to what I want it be like. For my guitars and ukuleles, I use the bandsaw, the router and pillar drill and not much else in terms of machines. I make jigs to be able to try and apply a consistent result to the woodmangling.

I feel a tad guilty of using Dave Neale's company to make the templates and jig this thread is about. I was going to make this jig in ply/mdf/wood, but found a cad drawing of a jig and decided it would be more accurate made by Dave.

If I were in production, and had an order for 3 Dreadnoughts, then I would have to consider the use of a CNC router for consistent output, any luthier business would have to consider that. In fact I'm sure such machines are used elsewhere in the commercial guitar making business. But, there are still some who would make their instruments by hand.

Mine is a hobby. Thank you for taking such an interest in my hobby and my efforts within it. I shall decline your offer but am fascinated by the technology within it.

 

[Malc2098]

Dave, Andy, thanks.

Andy, you're dead right. Those violin luthiers have it dead easy!

 

[Malc2098]

Well, I promised photos today, so here goes.

I like a spreadsheet as much as the next man, and I could have set one up and applied the formula in my earlier post to give me all the fret spacings for a concert ukulele. But why bother when the tables are readily available on the internet.

So armed with a table, i set about drawing a template for a cutting jig in Sketchup.



I was able to send that, and one for a 25.5" scale length guitar, to Dave at Lasercutz and he converts them to CNC friendly files for his laser machines and cuts the templates.

The centres of those holes are exactly where the frets line up. So if I stick the fretboard blank on to the template and the jig has a pin in it the same size as those holes exactly where the saw will cut, I should be able to make a cut, move the template and blank along one hole, rinse and repeat until all the slots are cut.



So what I needed next was a jig to support the template and blank and allow it to move along without any play in it up and down. I also need the jig to support a saw exactly vertically and laterally so that it was always at 90 degrees to the centreline of template/blank.

I was going to make this jig from ply/mdf/wood, in fact anything I could find in the workshop. Until, that is, I found a CNC pattern for one.



I sent this to Lasercutz and this is what came back.


Except for the bearings. I got them elsewhere.

So I set about assembling the jig.







And here is how it will work eventually.



I know, I know, it's the wrong sort of saw. I plan on buying a gents saw which will have the cutting edge parallel to the rib along the back and I can adjust the jig so that the saw will be limited to its depth of cut as the rib rests on the bearings.

 

[novocaine]

Very nice and should be ideal for what you want.

Till you make a 8 string fan fret. :lol:

I took the other approach an practiced cutting fret slots till my arms felt sore. Now i do them free hand. :lol:

 

[Malc2098]

Dave from Lasercutz and myself agreed this prototype was not quite as sturdy as it could have been due to the minor variations in the acrylic thickness, making the tenons a tiny bit loose in their mortices.

So he cut another one which I've glued together. Much more sturdy and stable this time.

There are four short SS rods sticking up in the corners that contain the templates and only let them slide sideways. There's another little SS rod right in the middle that the holes in the template locate on, the centre of each is the centre if the fret slot. The bearings above the template are adjustable sideways to get them spot on the mark and are adjustable up and down for different thicknesses of fretboard and different depths of saw.

 

[Malc2098]

Just about ready to start cutting the fret slots for the two Concert Ukuleles.

First job is to cut the nut end square and stick a blank fretboard onto the their template with DST making sure that the nut end centres exactly over the first hole and that the yellow centre line (for dark wood varieties) marries up with the lasered centre line on the on the template.



The template and blank assembly can now be located within the jig and the the template nut hole located onto the registration pin directly underneath the saw.



In my enthusiasm to get going, I forgot to measure the fret tang depth in order to set the depth of cut before I got called in for dinner! More tomorrow.