Acoustic Guitar Construction

Number Nine 04/18/21

Back when I was making number 8, the Venetian cutaway, my friend, Otto, wanted to try bending some wood. Otto is a boat builder and cabinetmaker of great excellence, but hadn't experienced bending with heat.

I still have a few short pieces of red oak so I profiled two sides for an OM and sanded them to .085”. He bent the waists on my hot pipe and the bouts on my crude Fox bender. I gave him dimensions for a head block, a pre-cut piece of 1/2” plywood for the tail block, and sent him home with a female mold. He put them together and installed some pre-made linings he bought.

Then returned it to me saying he was in the middle of a large cherry cabinet assembly and didn't have the time. The bass bout had cracked some in bending, so I'd sent him home with a dollar store tube of super glue and told him to screed it into the cracks with an old credit card, which he'd done.

Prior to this I'd been talking with my professional luthier friend here, Kjell, about wanting to do two things new to me, 1) make some parlor guitars and 2) use my same long 25.4” scale and OM body but make it a 12-fret to the body guitar, pushing the saddle down further into the center of the lower bout. Kjell explained that Martin had made a very small but splendid edition of that very same thing on their 000 short scale model for Norman Blake and he thought they were excellent sounding. Attaching a photo of my layout drawing. Bridge ends barely catch the X brace, and the distance from the sound hole to the X is 1-5/8”. We'll see if it works.

I had on hand a couple more Stew Mac AA unsanded cedar top billets. Glued a pair up, made a minimal 3-line rosette that fit a 3/16” dado, two lines mahogany and one maple. Bent the rosette strips on my hot pipe and clamped them around a larger scrap of PVC pipe to dry. Top was .115” before leveling the rosette and sanding.

Made my usual Don Teeter inspired 1/4” wide white pine bracing, selected from the portions of #2 common white pine boards that have vertical grain, lumber yard material. Had a few more short pieces of red oak so made a 3-piece back with maple divider stripes. My 14” Grizzly band saw won't re-saw wide enough to make a two piece back.

Bindings are also from maple on hand but I changed the down-cut 1/4” router bit in my binding router fixture and didn't get the offset correct on reassembly so ended up with bindings .130” thick x .25” high, more difficult to bend and tedious to glue. I normally make bindings .100” thick but I like the looks of these.

Routing the binding rabbets pulled a chunk of oak from the side about 3/32” wide x 3/4” long. I found my old can of Durham's Rock Hard Water Putty and screeded some in and sanded it. Dries yellow like old ivory, so took a tiny dab of burnt sienna from a tube of artists' oil paint on a cue tip and stippled the putty. Cue tip in photo points at the repair, looks almost similar to the dark grain to the left of the fix.

Back in the '70's I could buy half pint cans of colors in oil. Wasn't building guitars but could start with a wash made of a little raw umber, for instance, followed by burnt umber, raw and burnt sienna, etc. and the final finish would have great depth and richness. Start with plain old pine and make something look like lots of varieties of wood. Can't find half pints of colors in oil any more.

For #8, the cutaway, I made a little wash first with mineral spirits with a dab of thalocyanide green from an artist's oil tube applied with a rag to the black ash body. Followed this with two coats of Zinsser Seal Coat tinted orange with dye to make it look a little more vintage under the subsequent 3 coats of satin wiping urethane. Did same Seal Coat part on soundboard for this one.

This time I found something new to me in the local Ace Hardware. ZAR interior semi-transparent oil stain, color “Vintage Modern” which evened out all the old and fresh-cut red oak to look uniform. I think buying other of their “colors” will let me mix/blend/build up tone and depth similar to what I did in the '70's with the old colors in oil. Sometimes old dogs stumble over new tricks.

Unfinished neck is African mahogany with a 1/4” maple center stripe. (I already sent Herman a photo showing it more aligned than the end result on #8, hah!) My usual simplified version of a Spanish V joint attaching a maple headstock veneered with red oak. Assembly with body is via two 1/4-20 threaded K-D fasteners and cross dowel nuts. Fretboard to be maple w/zero fret, along with maple bridge.

For two years after I had my cataracts removed I had double vision, finally cured in two operations by the ace-of-the-world at this in Ann Arbor, an optical surgeon in his '70's at the University who could have retired years ago but thankfully likes doing what he's good at.

For #5 I routed an inlet for a mother-of-pearl NT logo (Native Timbre) in a light sycamore headstock veneer. Did this with my 50 year old Sears router with trigger switch in the right-hand grip, no problem. Then I got double vision and couldn't even come close to staying in the lines on #6 and the subsequent builds. Resorted to gluing the logo into the center of a wider cavity and then mixing black dye with clear epoxy and using that to border the MOP.

I actually like the black border as contrast to the MOP but wanted to try this one like somebody who knew what they were doing, and for a light headstock veneer it isn't world class but it will do. Out of MOP, so just cut a logo from Corian. I have a lifetime supply of that for nuts, saddles, and logos from a sink cutout.

Still lots of opportunities for getting off in the weeds but getting closer to being complete. Keep safe out there.

Looking good, it is all coming together. I notice you were using a wipe on urethane. I just finished a top on an older guitar of mine with satin wipe on poly. What an easy process and it really had a good look. I was got by and was happy with no leveling the final coat. I am surprised it is not used more often. Polyurethane is used by lots of factories now. Wipe on is just diluted polyurethane.

Number 9 Done 11/03/21

Too hot to work on #9 most of the summer and busy with stuff Pam used to do as well, slow progress. Started shop pellet stove 24 October, however and been making small progress, or retrofits, since. This one got badly off in the weeds somehow (photos, fretboard extension and bridge).

Way back about #3 build I read something Cerpilowski said about Martin laying side assemblies with kerfing soundboard side down on a sanding disc to kiss the perimeter all around, in order to mate with soundboards.

Then, he alleged, they tilted the upper bout from the waist into the disc somewhere on the order of a degree more. This made the soundboard slope downward marginally toward the neck from the waist in order to give the fretboard and string height a better run at the saddle height.

My luthier friend here, Kjell, told me the guy he worked for first did just the opposite, slanted the soundboard down toward the lower bout end from the waist.

Back then I had an Autocad clone 2-D software that would work on an earlier version of Windows and I did the Martin concept layout based on the waist to neck distance of the OM silhouette I was building. I can't recall what part of a degree or degrees it might have been but it amounted to a .125" drop at the neck.

If I pushed down on the side/endblocks/kerfing assembly in my female mold on the end block end and pulled it up, pivoting about the waist on the upper bout end where the neck attaches so it stood proud at 1/8" and clamped it there I could rout off the part of the upper bout standing proud of the mold.

Been doing this all along starting with #3. Somehow it got badly wrong this time, too much angle (FBextension.jpg). Otto started the sides/endblocks/linings assembly on this one as he wanted to learn how to bend the sides, then brought it back to me to finish, saying he was building a big bookcase in cherry with ebony inlays. It would be easy to blame the miscalculation on him but he's a master boat and furniture builder and he didn't do it, it was me.

I thought momentarily that the 12-fret neck instead of a 14 fret neck could have explained it but without CAD it would be hard to determine, trigonometry having long deserted me, but at some point I 'll draft it out manually and see.

Thought momentarily of putting masking tape on the sides of the fretboard extension and the soundboard and just screed Durham's Rock Hard Water Putty in from both sides. No way I could taper a piece of wood for both sides close enough to look any better than staring at the gap. Don't like it but it is what it is, remain open to suggestions, probably won't do anything about it.

Finally a little cooler this fall, worked up the bridge and installed. Again, I knew what the distance from the zero fret is supposed to be to the leading edge of my quarter-inch wide saddles. I scratched a mark on a cheap aluminum yardstick at that point, and have discovered with earlier builds that tuning to concert pitch shortens this distance by a hair over 1/32". So invariably position the bridge a thirty-second beyond the mark.

But of course this time strung up it ended being too close to the zero fret by 1/16" (saddleFX.jpg, before intonating saddle). I must just be getting addled or senile in my old age. Now the thing is to make a fixture to run a router with in order to widen the slot for the saddle.

Did this once before for #3, and, since my bridges are same size/form to locate against I could use that fixture, padding it and clamping it against the soundboard.

And not really a micro-adjustable method of changing the depth or offset of the router bit to widen the saddle slot in order to move the saddle farther away from the zero fret. I could, and did, lower the bit to eyeball the depth in the existing bridge. Eyeballed the offset needed, glued a thin strip of wood with two thicknesses of artist's 20# drawing paper to the edge to guide the router bushing against, and just before supper Sunday night, routed the pass.

Still too narrow to shim the saddle back a sixteenth. Pulled my paper and wood strip off my guide, found a slightly thicker wood guide strip, sanded it down a little, attached with 3 dots Elmer's Glue, ran a second pass. Just right. Whew! Saddle slot now accommodates a 1/16" pine shim and a .251" wide piece of Corian for a saddle.

Hooking and unhooking strings from the bridge end trial fitting a wooden saddle for height, I broke the 3rd, .024" string. Had extra strings in all sizes but that one. 7 mile trip to the music store in Albion yielded me one of the right gage but bright bronze, not phosphor - close enough.

Got the wood temp saddle to proper string height, mas o menos, used it to pattern the Corian saddle. The false nut (zero fret guitar) is at final form in Corian, relief at 7th fret right. Just did the intonation on the Corian saddle.

I think this one will be a talker also, already shows promise. The treble and mids are fine, the bass always sounds bad until they get played in a bit. And I'll settle for ergonomics and a good sounding box over woodwork any day, not that that makes me any kind of luthier.

And a non humidity-controlled shop means that the guitar sat there all of an unusually rainy summer and now I'm heating it with wood pellets. This translates to the fretboards always shrink, leaving some sharp fret ends protruding but since my necks are removable with two quarter-twenty screws, when the strings need replacement I'll file them down some more.

Lastly, photo of #9 next to old #2 (with 6mm underlayment plywood soundboard) for comparison of bridge placement on identical SC OM silhouette bodies.

Sound files forthcoming in a couple weeks after playing it in a bit.

Congratulations on number 9! The guitar looks great.

My luthier friend here, Kjell, told me the guy he worked for first did just the opposite, slanted the soundboard down toward the lower bout end from the waist.

I started doing this a few guitars back. It allowed me to standardize the neck angle and set the geometry or projection of the neck plane over the saddle position sanding the lower bout. I had not heard of others doing it. Now I know.

We played music in my shop Friday night, five of us. 3 Martins, 1 Guild, and my old #2 with the 6mm underlayment plywood soundboard. Passed #9 around so everybody could play it and I could hear their different techniques. Dan's Guild is pretty loud, but they all agreed #9 was louder.

Made a quick one-take pass at the old DAK Mp3 & Wave Editor in the cold basement and made a short sound file, #9_MCBc&d_SJI_Am.mp3.
Bass has improved greatly in a week.

That was fun!

That WAS fun! Git sounds good.