Help needed with classical bolt-on neck

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jonwallace
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Help needed with classical bolt-on neck

Post by jonwallace » Sat Jan 14, 2017 1:20 am

I understand that the nut needs to be tilted up to achieve the correct string height at the saddle.

Originally I assumed that the top of the neck was co-planer with the flattened upper bout and the fretboard wedge extended the FULL LENGTH of the fretboard and would therefore would sit flush on the top of the neck and be continuous over the upper bout.

However, the books actually states that the wedge only extends to the 12th fret, so I think I have completely misunderstood how the wedge and neck joint work.

Can anyone help explain this to me?

Thanks
Jon

johnparchem
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Re: Help needed with classical bolt-on neck

Post by johnparchem » Sat Jan 14, 2017 2:35 am

jonwallace wrote:

... However, the books actually states that the wedge only extends to the 12th fret, so I think I have completely misunderstood how the wedge and neck joint work. ..,
Are you sure? The ones I made the wedge tapers off closer to the sound hole than the 12th fret. It seems to me that your original assumption was correct. Having the wedge eliminates the need from sanding the reverse from the underside of the fretboard extension.

jonwallace
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Re: Help needed with classical bolt-on neck

Post by jonwallace » Sat Jan 14, 2017 2:53 am

It states it in section 4.6.12.3, 2nd paragraph below Fig 4.6-40.
I'm sure I read it somewhere else too - probably in the Build volume which I don't have to hand at the moment.

Thanks for your reply.
Jon

jonwallace
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Re: Help needed with classical bolt-on neck

Post by jonwallace » Sat Jan 14, 2017 3:11 am

On reflection, I can understand why the wedge extends only to the 12th fret - it is the centre of the rotation that is being applied.
Also, the wedge is made from neck wood, so it may not look right sitting on the soundboard.

I guess I just don't understand how the fretboard extension will sit flat on the upper bout.
Jon

johnparchem
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Re: Help needed with classical bolt-on neck

Post by johnparchem » Sat Jan 14, 2017 4:35 am

You need to look at the Build book. The figure you mentioned (4.6.40) was a traditional way of dealing with the forward angle; that is tapering the fretboard past the 12th fret so it lays flat. No mater what method you use the bottom of the fret board should lay flat on the neck and the top. The build book describes how to build a bolt on bolt off neck where there is a wedge glued to the underside of the fret board.

If you look at the build book you will see a clear example in figure 16.1 where the wedge goes to about the rosette. As the wedge is an extension of the neck wood it looks natural filling in the gap. The other option as described above is to taper the fretboard removing the wood that keeps the fret board from laying flat. I guess it is a matter of choice between the aesthetics of having the neck extend down with the fret board versus having the fret board start tapering from the 12 fret.

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Steve.Toscano
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Re: Help needed with classical bolt-on neck

Post by Steve.Toscano » Sat Jan 14, 2017 11:17 am

jonwallace wrote:I understand that the nut needs to be tilted up to achieve the correct string height at the saddle.
To dispell the myth.....
It doesnt 'need' to be. I build my classicals with the upper bout of the soundboard co-planner with the neck. Flat all the way from the nut to the soundhole. Useing traditional spanish style construction.
To get the right height at the saddle i adjust the height of the fretboard (usually works out between 6.25 -6.5mm).
My solera is setup with slightly more then average top dome for a classical - in the lower bout only - ive never measured it but i think around 25foot.

johnparchem
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Re: Help needed with classical bolt-on neck

Post by johnparchem » Sat Jan 14, 2017 11:39 am

Steve.T wrote:
jonwallace wrote:I understand that the nut needs to be tilted up to achieve the correct string height at the saddle.
To dispell the myth.....
It doesnt 'need' to be. I build my classicals with the upper bout of the soundboard co-planner with the neck. Flat all the way from the nut to the soundhole. Useing traditional spanish style construction.
To get the right height at the saddle i adjust the height of the fretboard (usually works out between 6.25 -6.5mm).
My solera is setup with slightly more then average top dome for a classical - in the lower bout only - ive never measured it but i think around 25foot.
I agree, The measured Hauser 1937 plans drawn by Richard Brune slopes the fretboard from the nut treble side to the bass side of the saddle end of the fretboard to achieve the correct geometry. The longitudinal slope takes care of the average saddle height, the horizontal slope deals with the fact that there is often 1 mm difference in the set action between the two E strings. Sloping the fretboard, thick treble to thin bass keeps the saddle height closer to the same bass to treble.

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Trevor Gore
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Re: Help needed with classical bolt-on neck

Post by Trevor Gore » Sat Jan 14, 2017 1:40 pm

There are many methods of getting the neck angle both right and wrong on classical guitars.

So whilst Steve is right, he is using a different construction method (solera rather than dish) where the correct action and string height above the soundboard is achieved due to a "mound" being built into the lower bout of the guitar. So we'll ignore Steve for now! (Sorry Steve!) :D

Dish construction lets you build both SS and CL guitars on the same infrastructure (which is why we went that way), but it means you have to approach the neck angle appropriately for the method. The basic bolt on method doesn't demand that the neck shaft and upper bout be co-planar. In fact it can't be using dish construction whilst using standard string height at the saddle and standard action. That means you have to bevel the underside of the fretboard over the upper bout because the neck is tilted forward by ~1 degree. A long wedge is not required using this neck joint method. Check out Build pp 12-15 and 14-9 for this type of joint. There's also the "theory" in Design Section 4.6.12.3

With the bolt-on bolt-off neck joint (Build chapter 16 and esp. section 16.4 for classical guitars), the neck initially has to be co-planar to the flattened upper bout, so that the pocket for the loose tenon can be routed, glued and leveled. But the fretboard plane still has to be tilted forward to get the right action and string height at the saddle, which is done using the long wedge under the fretboard. Where the wedge washes out is immaterial, but with the dimensions given in the book it tends to wash out near the 12th fret. Use a thinner or thicker wedge, or different action and string height settings and it will wash out somewhere else. The "wedge" is initially glued to the fretboard as a uniform thickness, full length slat, both to make the gluing easier and also to make planing the wedge easier after the slat has been glued on. It is possible to use a short slat, stopping at, for example, the 13th fret, if you run out of matching wood, but you then have the step to cope with when planing the wedge. It can certainly be done that way, but you need to be handy with a plane.

jonwallace
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Re: Help needed with classical bolt-on neck

Post by jonwallace » Mon Jan 16, 2017 12:47 am

Thanks to all, and especially the detailed explanation from Trevor.

Jon

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