Aspire and 2 rail sweep for fingerboard

[banjomanwv]

Im trying to figure out how to use a two rail sweep to make a compound radius fingerboard, or a straight radius even, anyone know how to do it?

[Brady Watson]

Post a pic of the fingerboard shape(s) in question.


-B

[Ajcoholic]

Im trying to figure out how to use a two rail sweep to make a compound radius fingerboard, or a straight radius even, anyone know how to do it?

To model the finger board, in either a constant or compound radius, I would do this...

- draw the edges of the fingerboard. dont connect the ends together, just draw the tapered edges from the nut to the tail end.
- draw an arc of the desired radius at the nut, going from the ends of the sides you drew and the desired height/radius.
- choose the two sides as your rails, with the arrows pointing from the nut to the opposite end.
- select the arc you drew as the object to sweep.

for a compound radius board, do NOT select the "scale cross sections with width" - which will flatten the radius as the board tapers wider down the length from the nut to tail end.

for a constant radius board, I would sweep along two parallel lines drawn from the widest part of the board, with an arc drawn at that end, and then trim to the actual tapered edges of the board. That will give you a true constant radius all the way down the board even with the taper.

[Ajcoholic]

I just did a few qucik samples. notice that the constant radius board has the same curve at both ends. the compound radius has the narrower end where the nut is, as a smaller radius and the body end a flatter radius.

nut end of example


body end of fretboard

[barrowj]

Andrew,

I never seem to be able to view your files on Photobucket, any ideas. I seem to spin forever then just blank.

Joe

[Brady Watson]

FYI - most fretboards have the metal put in straight without curvature - on guitars anyway. So, projecting onto 3D surface is only required if you need the .023" bit to follow the curvature of the neck. Not sure how banjos are done, but most guitars go in straight.

-B

[banjomanwv]

Brady the problem with that is the bits only cut so deep. The fret slots need to be .090 on a banjo as standard. With a 8 radius it will hit in the middle of the board and by the time it hits the sides its already deep in the middle. by the time you go .090 deep on the edge it makes it like an accordion. If you start with a board that's .200 it leaves .160 at the last fret in thickness, you then have a slot .090 deep...that's leaves .050 and that's not much so the more meat I can leave in the middle the better

[banjomanwv]

Brady it worked just as you said, thanks so much...

[Ajcoholic]

FYI - most fretboards have the metal put in straight without curvature - on guitars anyway. So, projecting onto 3D surface is only required if you need the .023" bit to follow the curvature of the neck. Not sure how banjos are done, but most guitars go in straight.

-B

The only guitars with a flat board are classical. All others (acoustic or electric, bass guitars etc) have varying radii generally from 9" to 12"

Frets of course have to be curved to follow the curve of the board. Most companies run their wire through a bender that matches the boards radius.

In most commercial slotting operations, a .023" saw blade just cuts a straight slot through the board. The fret slot is deeper than the fret tang at the middle, but that usually gets filled with glue anyhow.

If you really need the slots cut the same depth as the tang than you can certainly do so as stated.

Ive made a whole lot of fretboards over the years for various guitars - but I have a small table saw set up with a slotting blade and do it the old way (not CNC). I radius by sanding, although I do machine contoured radius blocks on the CNC router. Im not production, but I used to make 4 to 6 custom guitars a year.

[Ajcoholic]

The only thing you will also notice, is that with the compound radius board, the thickness at the edge of the board will remain uniform as you go from nut to body end.

With the constant radius board, the thickness at the edge will decrease from the nut as you go along the board to the body end, but the thickness at the center down the length will of course stay the same thickness.

You prob already knew that... it only comes into play if youre binding the edges.