Neck Angle Geometry

[Joey Herscovitch]

Hi Everybody
Just joined up & have enjoyed reading some of the posts & discussions on this site. They are very informative. Well I'm finally putting time into an acoustic guitar project that I started, would you believe, 29 years ago. Sort of tells you I'm a little older than 29. It's a little unusual in that the back & sides are flamed red oak (very pretty) that I started w/ a Luthier from the Vancouver, Washington area in 1979. It also has a shorter body length (I call it my Mini Dreadnought). It has a Sitka Spruce top & Black Walnut binding w/ Purple Heart purfling.
Right now I have finished the body & am ready to tackle the tricky task of fitting the neck to body joint. (I've read FF's article on checking neck angle at Frets.com.) I'll be using a traditional dovetail, & I have no trouble w/ the setup for that, BUT my concerns are regarding the neck setback angle. Specifically, when you cut a cavity into the body that is square to the top & a neck tenon at an angle less than 90 degrees, you end up w/ a fingerboard tongue that climbs away from the top. For example, by my layout, w/ the base of the neck cut at an 89 degree angle there will be a 1/16" gap between the end of the fingerboard tongue & the top. Smaller angle, more gap. While I realize that I can close this gap w/ clamping pressure when gluing, won't this cause either a dipping of the fingerboard after the 14th fret, or a lifting of the top in the same area, or both? Am I missing something or is this corrected by normal tensioning of the strings? Other than the Taylor system, on a glue joint would you ever consider relieving the fingerboard into the top at this angle to accomodate? Lots of questions.

[mathieu thomas-guy]

What I do is to put a dome in the top so that it bulge and become in line with the back angle (about 3-4 degree). Check with a drawing of your guitar with the projected bridge height (actually string height- around 7/16 plus 1/8 bulge at the brige ), usually you will need about 1/16 (your gap!) of "curve" in your braces (I use two), carve this with your plane and sanding block. Of course the linings must be shaped to fit the dome with the bowl, as Doug points out; just use the bowl to glue your braces too, perfect fit! That way you will have room for a comfortable action, wich is the "nerf de la guerre" for a fun guitar.
For your actual project (I guess all your braces are flat-use less back angle again check your drawing) you could shim and use a back angle, or forget the back angle (use a square joint-easy) and shape your fingerboard thin at the nut and thick at the soundhole wich look weird but acheive the same result. Taylor joint is really cool but best suited to CNC machinery.

[Joey Herscovitch]

I actually have done what Doug suggested, with a flat brace under the fingerboard extension & flat bridge plate, but w/ a 25' radius on my other braces. This does give me a slight angle & I may go w/ this & adjust my bridge thickness to get the correct relationship that Jim Bancroft (& Frank Ford) talks about, if it looks like it will work.
Oddly enough in reading the section on truing the fingerboard in Campiano & Natelson's book they say "Focus your attention between the first & fourteenth frets. A slight dip from the fourteenth fret to the end of the fingerboard may be ignored" That's what I love about all this, everybody's got an opinion w/ different reasoning & it helps in drawing a conclusion.

[Tim Mace]

I've been thinking a gentle incline on the neck block to match the neck angle could aleviate the 12-14 fret dilemma..what about it?