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Fret Slot Jig

Ted Calver

Ted Calver

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Time to get off my duff on making Cigar Box Guitars for Christmas gifts. I recalled the slot cutting jig used in this bass build by Dave Black and thought my Corian scraps could be put to good use. Here's my version:

A few counter top scraps:
Jig 021.jpg
Some Helicoil threaded inserts and 10 x 24 machine bolts with washers and lock washers. Slots allow for lateral adjust-ability:
Jig 016.jpgJig 017.jpgJig 025.jpg

Rounding a few corners and shortening sides to allow clamping room, if needed. The fret saw rides on the top of the jig, which is sized to cut the slots 1/32" deeper than the flange of the fret wire. I hope that's deep enough. If not, I can add shim stock under the template to deepen the cut.
Jig 032.jpg
Squaring up the side that will be fixed in place:
Jig 036.jpg
The small pin that will index to the fretting template:
Jig 037.jpg
Some double sided tape on the bottom of the fret board to hold it on the template:
Jig 039.jpg
Voila! We have a fret board. A test run on a 1.5" wide fret board (using scraps of Brazilian Koa left over from a flooring job...I left the finish on to see if it would work). The StuMac template is on the bench with double sided tape on it to hold the wood blank. I discovered that is not enough tape because I could feel the blank move:
Jig 042.jpg
The stack of fret board blanks. Various lengths 3" wide planed to .27" thick. I should be able to get a few guitars out of this.
Jig 047.jpg
 
Thats a nice looking miter box Ted and your are going love that setup. I started making my own temples out of the Aluminum 4' measuring sticks from HF and a 1/16" slotting blade from Grizzly. I cut the measuring stick in half and then notch the half's on both sides with different Scale Lengths. Way cheap way to have several different SL and you will want more trust me.

Oh and your going to love that Brazilian Koa for fret boards in fact I just used up all of what I had that some guy you might know sent me:D:wave::wave:
 
Thanks for the kind comments. I can't believe you let me get away without a razzing. I must not be the only one who can't remember which way to crank the saw blade.:D
Jig 047B.jpg
 
Hi Ted.
Unless Corian has changed its composition since I met it when I was at school, that jig is going to ruin any hand saw that you use on it, specially your japanese ones which are delicate.

When we used it at school we had to use widia teeth circular saws, and special steel bandsaws to cut it. Any other hand tool ( saw, chisel, or rasp) that we used was ruined in a few strokes. If you cut the initial slot with your saw, I fear you have ruined it already. If not you will ruin it in a few cuts when the teeth will rub on the sides and you'll wear down the set.

This was 25 years ago, so they may have changed the composition to make it easier to work with but that I don't know. In this case I wish to be wrong for your benefit.
 
Toni, Good thought. I was worried too, but the saws used to cut fret slots have no, or very little set, so all I had to do to was relieve the sides of the jig at the bottom of the slot with a couple of swipes of a file to eliminate any chance of the corian messing with the teeth. I cut the jig parts on my table saw with a carbide blade and on the band saw with and old blade--no problems with either. So far, so good, but I've only cut one board. If needed, I'll face the slots with some UHMW plastic. I was more concerned with cutting through the finish on the flooring with my fret saw. The flooring finish is supposedly guaranteed for 50 years and has a high silica content. To protect the fret saw I made the first couple of swipes through the finish with an old Japanese pull saw from Lowe's, then finished the cut with my good fret saw. The small added width of the first cut helps set the fret wire, since many people run a small triangular file across the fret slot to do the same thing.
 
Ted Calver said:
Rounding a few corners and shortening sides to allow clamping room, if needed. The fret saw rides on the top of the jig, which is sized to cut the slots 1/32" deeper than the flange of the fret wire. I hope that's deep enough. If not, I can add shim stock under the template to deepen the cut.
Click to expand...

It depends what you mean by 1/32". Are cigar box guitars the same basic neck geometry as regular guitars....somewhere around a 25" scale length, about 1 3/4" or less at the nut, and somewhere around 2 1/4" at the body (obviously not exactly those figures, but somewhere around those numbers), and does the neck have a radius? If so, if you went 1/32" under the tang measured flat across, that won't be enough. For something like a 12" radius, when you get to the body side of the neck, the edges of the fingerboard are about 1/16" lower than the center. That's assuming that you radius the board perfectly.

If you want to know how to calculate this, look up something called the Versine function. It's a trigonometric function that will allow you to calculate the height of the center of an arc above a chord.

:huh:

Or just go here, plug in the numbers for your particular neck, and see what pops out. :)
http://liutaiomottola.com/formulae/sag.htm

The versine function is also called the "sagitta", presumably because when you draw it out, it resembles a bow and arrow.

Anyhow, that little calculator will allow you to calculate exactly how much the ends will be lowered after radiusing. Calculate at the body end of the neck since that is the worst case (the wider the fingerboard, the more the ends drop) :)

You can always just deepen the slots freehand after radiusing, so it's not big deal either way. Just be careful not to widen the top of the slot when you do it.
 
John Coloccia said:
It depends what you mean by 1/32". Are cigar box guitars the same basic neck geometry as regular guitars....somewhere around a 25" scale length, about 1 3/4" or less at the nut, and somewhere around 2 1/4" at the body (obviously not exactly those figures, but somewhere around those numbers), and does the neck have a radius? If so, if you went 1/32" under the tang measured flat across, that won't be enough. For something like a 12" radius, when you get to the body side of the neck, the edges of the fingerboard are about 1/16" lower than the center. That's assuming that you radius the board perfectly.

If you want to know how to calculate this, look up something called the Versine function. It's a trigonometric function that will allow you to calculate the height of the center of an arc above a chord.

:huh:

Or just go here, plug in the numbers for your particular neck, and see what pops out. :)
http://liutaiomottola.com/formulae/sag.htm

The versine function is also called the "sagitta", presumably because when you draw it out, it resembles a bow and arrow.

Anyhow, that little calculator will allow you to calculate exactly how much the ends will be lowered after radiusing. Calculate at the body end of the neck since that is the worst case (the wider the fingerboard, the more the ends drop) :)

You can always just deepen the slots freehand after radiusing, so it's not big deal either way. Just be careful not to widen the top of the slot when you do it.
Click to expand...

John CBGs are flat fret boards 1 1/2" wide and anything from 14.5" to 27" SL and some times even 30" SL No radius
 
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