Thickness tapering a Classical Guitar Finger Board

[Cameron Petersen]

I'm somewhat new to guitar building ( 1 steel-string and 3 classicals)

I wondering whether or not it is feasable to thickness taper a finger board for a classical guitar on a drill press using a "Wagner Planer". If so, could someone furnish an outline on a jig, and the procedure??

thanks.

[Russell Vance]

What does thickness taper mean?....does it mean you wish to make the board non-parallel between the face and back surfaces and if it does, why? I know little of classical construction and this is a genuine 'why' - do they use tapered boards to set initial action geometry?.

If you just wish to taper a fingerboard from one end to the other - double side tape (with the skinny tape not the soft thick double sided type) a fingerboard to a tapered or shimmed piece of MDF , set up some guide rails either side and ease the board under the planer head with a couple of light cuts using your drill press platen height adjustment to bring up the work to the head.

[Cameron Petersen]

I've been using Cumpiano's book. Instructions indicate the board thickness at the nut to be at least a 1/4 inch and the thickness at the 12th fret 1/32 inch less. He builds on a work-board. I find it very difficult to get the proper geometry even with a pre-tapered (not-parallel between the face and back surfaces).
Is there a more simple way of building whereas one would not set the initial action geometry with a tapered board?
thanks.

[David Payne]

I have built a lot of classical guitars and repair many older ones. This tapering of the fretboard is one tradition I totally disagree with (sorry Master Torres).

Tapering it as you move towards the saddle just increases the problem of having a saddle that is too low and therefore little or no adjustment range later on when the neck slowly rises over the years (since there is typically no truss rod). I have seen dozens of old classical guitars in my shop where the action has grown higher over the years and the saddle has been filed down little by little over the years to attempt to get the action right. The latest one I worked on had the bone saddle filed so low that the 1st (E) string was touching the wood of the saddle when I got it.

Having a really low saddle creates a low "break" angle which transmits less sound. You don't want an extremely high saddle either because it may over stress the soundboard and make it "belly" too much. The ideal is to have 3 -3.5mm at the 12th fret between the top of the fret and the bottom of the bass string with less under the treble strings.

The saddle should actually taper up to the G and D strings because they are the ones that move wildly compared to the others. The from the D string to the low E it can actually taper lower. If you have a really low saddle these adjustments are hard to make.

Classical guitars are zero neck angle so you have to do quite a bit of measuring with a long straight edge as you build to make sure your string and saddle height is appropriate. To me this is one of the hardest things to get right because you have to anticipate the neck rise (neck relief).

Because of this issue I have broken with tradition and adjust the fingerboard angle and thickness to match the geometry that I am targeting. I have also begun committing another sin of using a truss rod. It just seems like the right thing to do if you want the guitar to remain playable over it's life and have future options when it comes to adjusting setups. There are no "neck resets" in the classical guitar world.

I would like my guitars to be able to be handed down from generation to generation and not unusable early in life.

Sincerely,

Dave

[Cameron Petersen]

Thanks Dave.
At the risk of coming across somewhat ignorant, isn't adjusting the fingerboard angle and thickness the same as "tapering it in thickness"?
I'm at the mercy of learning from books. Do you know or can you recommend one that teaches a different method of achieving the proper geometry being discussed???

[David Payne]

Cameron,

A fingerboard that tapers in thickness as it approaches the bridge will make the saddle lower than one that doesn't given a standard string height (usually measured at the 12th fret). A fret board that doesn't taper will have a slightly higher saddle (string height being equal).

On steel string guitars the height of the strings and saddle are set by the neck angle. Since many SS guitars have a domed top (made by curving the braces) the neck can have a negative angle (headstock slightly lower than where it meets the body). This negative angle helps get the saddle height where you want it.

Since classical guitars are generally true flat tops the neck is parallel to the top making it a 0 degree neck angle. Having said that, now the only way to control proper string height and proper saddle height is to change the following:

1. Fretboard thickness
2. Having a fretboard that gets thinner as it approaches the sound hole (lowers the saddle)
3. Having a fretboard that gets slightly thicker as it approaches the sound hole. (raises the saddle)
4. Stiffening the neck with a truss rod, graphite strips or other really stiff materials to control neck bow (caused by string tension pulling the neck up).

Fret boards are not flat under string tension. Usually if you clamp the strings down at the first fret with a capo and fret the strings at the 12 or 14th fret you should be able to get a .010" to .020" shim under the strings somewhere around the 6th to the 8th fret. Without a slight amount of bow (neck relief) the strings will buzz when fretted. If you don't have one a set of spark gap gauges from a auto store is easy to get and cheap.

Too much neck relief will raise the action (especially over time as the neck gives under tension). Not enough neck relief will cause buzzing and playability issues.

It is a game of planning to get the action correct on a classical guitar while still getting a reasonable saddle height as well.

I will try to draw some pictures but if you get a chance read some articles by Kenny Hill. He has some in depth material on this and other parts of guitar setup.

Go to: http://www.hillguitar.com/

then click on "Luthier" and then click on the link "articles"

I can't find a direct address cause his site is built with frames.

Hope this helps,

Dave
Constantine Guitars