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Old 08-11-2017, 01:19 AM
dekutree64 dekutree64 is offline
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Join Date: Nov 2009
Location: Kansas City, Missouri
Posts: 1,263

Originally Posted by CabinetMan View Post
Redir, So I'm gonna go with a flat sound board. Since I have a good fit between the neck block and the neck tenon, I "ASSUME" that my neck angle will be correct? Correct?
It is preferable to have the headblock and neck top surface coplanar, but that alone won't create the correct geometry.

What is the target string height on your plan? (distance up from the soundboard surface to the strings just in front of the bridge). Typically it will be about 1/2" (12.7mm).

My magic formula is the fret plane projection should be 2-2.5mm below the target string height. (fret plane projection is where you lay a straightedge along the frets and measure the distance between it and the soundboard surface at the bridge location)

There are many ways to accomplish that. The neck angle, soundboard arching, rim profile, fingerboard thickness, and fret height all work together to determine the fret plane projection.

So for typical 12.7mm target string height, fret plane projection should be 10.2-10.7mm. To compare, a fully flat neck/soundboard with 6.3mm (1/4") thick fingerboard and 1mm fret height means your fret plane projection is just 6.3+1=7.3mm, which is a fair bit too low.

Put another way, for typical string height, a straightedge laid along the neck surface before gluing the fingerboard on should have a 2.9-3.4mm (about 1/8") gap under it at the bridge location.

As redir suggested earlier, arching the upper transverse brace and/or sanding an angle into the upper bout of the rim can give you the necessary increase in projection height. Or just angle the neck independently of the box and stick a wedge under the fingerboard extension.
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