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mzuch
03-04-2015, 01:57 PM
I know this is a ukulele board, but I’ve gone temporarily over to the dark side and I’m working on a dreadnought guitar with a 25.4” scale. I'm not a member of any of the guitar boards and thought I'd ask here first.

I don’t bother with a neck angle on ukes as I’ve found they’re not necessary, but I’m pretty sure that a guitar of this size needs one.

So I’m investigating various methods to determine the proper neck angle. My aim is to have a saddle that extends 1/8” above the bridge. The bridge will be 5/16” thick and the radiused fretboard will be ” thick in the center before frets are installed. The frets have a .039" crown height.

Robbie O’Brien and LMI have a video online in which he places a 0.98” to 1.38”shim at the saddle location and lays a straightedge with one end resting on the shim and the other directly on the soundboard where it meets the heel of the neck. He duplicates the angle with a sliding bevel and transfers the angle to the neck blank. He makes no mention of fretboard and bridge thickness. Using this method, I come up with a neck angle of about 2 degrees for my guitar.

In their book, Cumpiano & Natelson discuss a different method in which they lay one end of a straightedge against a fretted fingerboard at the neck joint location and the other end 1/64” to 1/16” above the top of the finished bridge. They transfer the angle to the neck blank in the same way O’Brien does.

For those of you who build guitars: how do you do this? Is a simple 1/8” shim sufficient using the O’Brien method? Or do I need to make the fretboard and bridge first (or properly thicknessed equivalents) as in the Cumpiano book? Any insights or advice are greatly appreciated!

JustVince
03-04-2015, 04:42 PM
Mzuch, I have the Cumpiano book here and read the part you describe. The 1/16'' above the finished bridge off a fretted neck with a straight edge sounds right. Start making your neck with angle you calculated, along with the fingerboard. Are you installing frets after the neck is installed or before? Remember to add in the fret height you mentioned if installing after. (I prefer to fret before gluing the neck). When you have these dry fitted to the body you can make adjustments to get it dead-on. You'll have the neck on and off 20 times before you glue it if you're like me (assuming its not a bolt on). I'm in Westchester , hollar if you need a hand. -Vince

ksquine
03-05-2015, 05:09 AM
I build guitars too. My neck angles are about 1.5 degrees. I say "about" because I cut the neck angle on the table saw and I can't really measure 1.5 degrees too well on the table saw. You need to sand the angle into the rim too or the fretboard won't sit on the top flush. The top needs to drop at the same angle as the neck in the upper bought. Here's what I do...
Assemble the rim, blocks glued to the sides and the linings glued in
Measure the body length, probably about 21"
Make a shim to sand the angle into the upper bought. The shim is just a piece of scrap wood that gets placed under the tail block to create an angle.
Math: Tanget(neck angle) X (body length)= shim height. Tan(1.5 deg) X 21" = .55" Adjust for your measurements
Place sand paper on a flat surface. The surface must be big enough for the whole rim but you only need sand paper at the upper bought area
Place the shim under the butt end of the rim and sand in the angle. You need to sand the angle just in the upper bought, not the whole body. Just past the widest part of the upper bought is where I stop

I realize that this isn't perfect....the angle changes as you sand more and more. But it works pretty well and things line up fine at the bridge. I adjust the neck to fit the angle on the body after the top is glued on.

Beau Hannam Ukuleles
03-05-2015, 08:56 AM
Ive never thought in terms of degrees.

Bridge 10mmish (remember you lose 1mm when radiusing the bottom to match the curve of the top), saddle 3-4 mm above that.

Point the top of the fingerboard around the top of the bridge