Acoustic Guitar Construction

Dave, I certainly did not take your good advice as any kind of criticism. I think you offered a sensible take on the question I raised. I just can't refer to something someone has done earlier and documented. And I think you're sure right about wood (my words now) being a bit of a moving and indistinct target. Little variations, virtually imperceptible, can stack up to seriously corrupt the best of measure-twice-cut-once projects.

Cake and cookies any time you want to come and visit.

Thanks very much for taking the time to respond, I appreciate it very much.

And Hans, you're vastly more innovative and creative than I am. Thanks for sharing your project descriptions with us.

Peter,

My approach is like John P's. I make the guitar complete with the neck glued on. Then I make the bridge exept for thickness. A straightedge is over the frets and I sand down the bridge to the situation where the straightedge is just over the top of the bridge (about 1 mm space). I have no min or max bridge thickness, but I aim for a 12,5mm (1/2") space between the top and the strings. I think if it is more than 14mm, my neck angle is off. But I did not have that yet.

Then pro's always claim, if you do the math right, all falls in place. Well, that is not my experience. Dry fitting the neck and its angle can be optimized before glueing. But the angle is always a tiny bit different once the neck is glued on. Not much, but a bit. For that I aim with my neckangle one mm higher at the bridge than the math tells. You can easily make a slightly high bridge work. A too low bridge in the beginning is a PITA.

Ok, not much of a help, I guess, but you will find your way amongst different approaches. Good luck.
Herman

Peter, I'm slow to get here but here's my two cents.

I have a friend locally who was a luthier at Elderly Instruments for 18 years. He says that Martin makes up bridges with heights of 1/4”, 5/16”, and 3/8”, since, as Dave and Herman have mentioned, the best laid plans often go astray.

He also said that a straightedge on the unfretted fretboard should equal the height of the bridge at it's placement if the neck angle is correct, or a straightedge on a fretted fretboard ought to be 1/32” high of the bridge, in order to affect a saddle projecting 1/8” above the bridge. Not sure if these two statements don't conflict.

Years ago when I lived in Texas and Bill Collings was in his former, much smaller, shop in Dripping Springs, TX (yes, I know it says “Austin” on his labels) I once walked in unannounced on a Saturday morning when Collings was absent but his shop foreman wasn't and gave me a tour.

They had a large concave sanding disc rotating on a potter's wheel so that they could put a spherical radius on the edges of the completed assembly of sides, end blocks and linings where the soundboards or backs would attach, simply by setting that assembly down into the sanding disc.

In conjunction with this I don't do anything spherical, being basically a heretic to actual luthiers, but somebody, I think Ken Cerpilowski the founder of this forum, had posted mentioning that Martin put their soundboard-mating assembly against a rotating sanding disc, concave or otherwise, and then after the surface was contacted all around, rotated it around an axis across the waist, to lower the height of the sides toward the neck block by a slight amount. Therefore, if the soundboard was actually flat, it would slope downward from the waist toward the neck by a little bit.

I drafted this out for the OM sized guitars I'm building back when I had a 2-D modeling software, and it amounted to an 1/8” drop toward the head block. My last 4 guitars, 3-6, have been constructed in this method. I bring up the neck block 1/8” proud of the female mold it's in, tapering back to flush at the waist. I mount my router in a long board with the bit projecting 1/8” and I rim the mold from waist to head block with 1/8” masonite to slide the board on and rout the taper into the sides and head block.

I don't glue or fasten my fretboards to the soundboard, nor do I glue in saddles or nuts. I aim for the fretboard end at the sound hole to be 1/32” above the soundboard before strings are installed and the tension pulls it down fine, no buzzing. Two K-D fasteners attach the neck and it can come right off, going in thru the soundhole with a 4mm Allen wrench.

I like to wedge in the nut, slightly, like a rifle sight, between the end of the fretboard and the headstock veneer, and I want a finger-press fit with my 1/4” saddles in the bridge slot, cut straight across.

There's a lot of difference between theory and result. I had to remove the bridge on #6 and make a taller one. So far #7, neck in construction, seems to be on track. An unstrung guitar, suddenly subjected to strings tightened to concert pitch, is going to move in subtle ways; e.g. my fretboard end now touching the soundboard. Then you have neck relief, neck set, and your desired string height above the 12th fret all affecting bridge and saddle height, some of which can be altered by a good truss rod. One of my Texan friends used to say “Wah, hail, if it wuz easy I'd be doin' it”.

Thanks, Will. Nothing like asking an artist how he does something...And then see how that compares to asking a non-artist the same question.