Official Luthiers Forum!

Looks like a great idea!

If it were me, I'd hinge the bar and move it over top of the blade. That would accomplish a few things. It would allow the bar to act as a one handed hold-down by springing it a bit. It would ensure that there would be no twisting force on the piece if the hold down was over the blade. And it would allow you to slot (then spline) the bar with the saw itself (with a wider blade) to guarantee accuracy.

_________________
http://www.chassonguitars.com

My sled is something like that. . but I have a hold down screw that semi clamps the board in place. I dont have a slotting template per se, as I would need one for every different FB you did .. even with the same scales, if the straight fret moves say from 9 to 7, thats another template. I use fretfind and print that out, then glue it to the FB upside down (print out the FB lefthanded for a righthanded guitar). The clamp board on my sled doubles as a hair line cursor, and I clamp the board such that the line on the prinout lines up besdie the edge of clamp rail board .. then cut away ...

BTW, I have to change the bracing layout every time the scales change as well .. because the bridge will move some, so you pretty much have to.

_________________
Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

Thanks for posting this info. It gives me some good stuff to go on as I get set to do this.

Tony, If it is not to much trouble would you post a picture of your sled? I like the idea that it can be used for any scale length without major setup time.

Josh

_________________
Josh House

Canadian Luthier Supply
http://www.canadianluthiersupply.com
https://www.facebook.com/canadianluthiersupply?ref=hl
House Guitars - Custom Built Acoustic Instruments.
http://www.houseguitars.com

One thing to keep in mind when you layout a multi-scale (fan fret) fret board is that unlike a straight fretted fretboaard you can not set the position of the scale increments based off the edge of the fretboard. In other words the upper and lower scale position as defined by a calculated scale chart must be plotted at the intersections of the 1st and last stings accordingly. if you plot the calculated scale increments at the edge of the fretboard then you impart and error at the string. Let’s say you want to do a 27.9 scale x 28.9 scale baritone for instance. If locate the saddle slot position based on the calculations and required compensation and you plot the fretboard increments per the calculations at the edge of the fretboard and use the 10th fret as your common fret (the single fret that is true perpendicular to the FB center line.) you end up with the sting contact on the frets at progressively wrong scale positions each side of the 10th fret. Each fret sound hole side of the 10th will be in a sharp position and peghead side will be in a flat position relative to the scale.

Some of you may have know that but just incase some one is trying a multi-scale for the first time and did mot know the scale position per the calculation need to be at the string centerline the dimension where the slot exits the fretboard is a dimension base on the angle the upper and lower scale fret positions at the outer string centerlines

Here is an image of the error that happens if you plot the positions perpendicular to the FB centerline and at the edge of the fretboard.



.027" flat at the first fret and it gets progrssivly less as you approch the 10th (if that is your perpendicular fret at both scales) and gets progressivly shaper as you pass the 10Th. my main point is on a multi-scale you must have a known outer string spread at both the saddle and nut and plot your scale spacings for the smaller scal along the centerline of the first string and plot the longer scale increments along the centerline of the 6th string. to get the incremental scale values correct.

Use the fretfind program Micheal .. it takes care of all of that .....

_________________
Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

where do I get it? Then you have to enter the spreads at nut and saddle I assume for with out that info your just guessing to be close. It seems to me that sting gauges used will affect this because a larger gauge set you will have to set the stings slightly more inboard so I assume this program takes that into acount.

Micheal,

Good point . . . BUT if someone's first instinct is to measure/plot scale lengths for a mult-scale fretboard perpendicular to the FB centreline at the nut extremes of the fingerboard then the other aspects of adapting to making such an instrument are going to be a real struggle for them I would suggest. Conventionally a perpendicular fret is used but you don't need to have one and if nothing is perpendicular then it gets even more interesting !!

There are two ways round this - either set your scale lengths at the fretboard edges when you have worked out the required taper and nut edge angle (which means that the outer string scale lengths will be marginally shorter than these) or do the simple geometry/algebra based on the string insets and recalculate the outer FB edge scale lengths. Well three ways actually - draw the outside string paths and plot the scale along these.

Let:

LS be the long scale length(measured along the string)
SS be the short scale length (measured along the string)
w be the length of the nut edge of the fingerboard from the outer edges of the FB
b be the distance along the nut edge that the bass string centre is from the outer edge of the FB
t be the distance along the nut edge that the treble string centre is from the outer edge of the FB

Then (if the outer strings run at a constant distance from the fingerboard edge) the scale length along the bass edge is:

FBB = LS + b * (w-b-t)/5

and the scale length along the treble edge is:

FBT = SS - b * (w-b-t)/5

In your example FBS would be 28.938" and FBT would be 27.868".

You can do the algebra to allow for the outer strings not being parallel to the FB edges or do it the third way above.

Technically having all the frets on a FB perpendicular to the centre lines and the strings splayed away from the FB centre line means the scale along the string paths are "inaccurate" but the "errors" are minute in the extreme.

_________________
Dave White
De Faoite Stringed Instruments
". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010

Michael - hence the Doolin instructions, i.e. taper, then mark the spacing/measure along the taper of the board.

I use this ...

http://www.fretfind.ekips.org/2d/index.php

This takes into account string spacing at the nut and bridge, with offsets at the nut. You cn place the straight reference point/line anywhere, even between frets. You can also I htink psecify tunings, but I dont bother going that far.

Changing string gauge may make some small theoretical difference Michael, but in reality its fine. After about a dozen multiscales, this works fine ... the first couple were all marked out by hand pre binding, after that taper. With this program I print it out and then glue it to the FB bottom, use my sled.

_________________
Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

You and I are saying the same thing, you have to know the distancce from the centerline of the fretboard to the nut intersect of the first and sixth string and the the same at the saddle so that you can calulate the angle the stings are relitive to the centerline of the fretboard and plot the fret incraments along the centerlines of the strings. First string=short scale, sixth string=long scale.

My biggest point here is; to do this right you have to know where the string centerline is at the nut and saddle. A small change in the angle between the string centers can cause major intonation issues.

I agree that for the common still string builder (my self included) the first thought is to plot both scales starting a the nut/string intersection and lay the divisions out perpendicular to the centerline of the fretboard. I have an inprocess drafting job that is directly related to this conversation. As soon as I started laying the two scale outs I noticed this.