Official Luthiers Forum!

I hosted my for thread here in OLF a couple of weeks ago. In fact, it was my first time participating here, though I have been a member for some time. I am currently rated "Mahogany", and you may not know of me, but I have been building professionally for over 50 years, my entire adult life! I am pretty set in my ways, so I may seem to be a bit "confident" (sometimes mistaken for arrogant) but as you get to know me I expect you will find me a gentleman. I am posting this build thread in the spirit of sharing a lifetime of experience in the hope that some among you will find my stye and knowledge useful.

The previous guitar was unique in my history of 650 instruments including at least 297 acoustic guitars. Actually, they all are, but this one was more so as it was a new template, non-dirivitive, and from materials new to me. The subject of this thread will be based on the previous guitar, which I called a "Couch Noodler", partly just because I am too clever by half, and partly because I really do expect it will be a terrific guitar for relaxing on the sofa or whatever.

This one will be European (Polish) Spruce over Brazilian Rosewood, materials very familiar to me. The string length is 25 11/32", also very familiar to me. At 14 1/4", the lower bout is 00sh, and the upper bout is narrow for me, at 10". The body depth will be less than Martin folks would expect, and it will be slightly wedged, maybe 3/16".

I do not use any templates for laying out my bracing. I am more interested in growth than I am in repeatability, so I allow each guitar the possibility of an incrementally smarter layout. Of course that leaves them open to the possibility of the opposite, but so far, so good. Using aesthetics to control the layout can be viewed as giving the subconscious access to the hands.

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Bruce Sexauer, luthier
http://mojoluthier.com

Looking forward to this one. I very much enjoy seeing how others build. I've found that there is always a good idea or three that I can fold into my own process.

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Steve Smith
"Music is what feelings sound like"

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George :-)

Watching this too!
The last 4 I have built have been in this size range and all their owners have described them as their couch guitar.
Thanks Bruce!

B

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My memory is so good, sometimes I remember things that never happened.

I appreciate you taking the time to share what you know, Bruce.

Bob


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Bob

Seen a lot of your posts on the Martin guitar forum. I expect your contribution will be incredible. Thanks for sharing.

There are builders in the other forums I share in, but mostly relatively unenlightened end users are the audience. It is pleasant to be talking to people who have a technical grounding.

I changed the paper on my double drum thickness sander this morning, and one of the rolls had a join in the 3” wide material with a splice piece added to hold it together in service, I assumed. So I went head and wrapped it on, started the machine, and all seemed well . . . Until I put the top through to level the rosette. The paper blew up and damaged the top. The top was around .170”, so I had room to recover, but lost the rosette. So, when I post pics of the rosette in this thread, sharp eyes may notice that while I did replicate what I had, it is not actually the same. Hard day, but made easier by selling one of the older (2018) guitars I had hanging around. Ship it out tomorrow. I’m in the house and on the iPad, so no pics till tomorrow when I get to my main machine.

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Bruce Sexauer, luthier
http://mojoluthier.com

This relatively inexperienced builder (in the middle of #8) is looking forward to watching you build one, Bruce!

I feel your rosette pain. This week I had some unacceptable gaps along the outside edges of 2 rings on my current build (I misjudged the glue swelling factor), so I had to rout along the gaps and glue in some additional veneer strips. It turned out really nice in the end, but I don’t enjoy the delays caused by the need to fix my own flubs.

I kind of feel bad saying this but... It's nice to know that someone with 50 years experience and 650 instruments under his belt still screws up in the shop occasionally

It's that human thing we are all guilty of.

I'll be following along. I really like the shape of this model.

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Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

I’d like to mention 2 design considerations that seem to be largely overlooked.

One: A fatal flaw of the acoustic guitar is that over time the top develops an “S” curve under tension, allowing the neck to tilt into the body. Many makers have attempted to address this by beefing up the neck block area. IMO, this is not the problem area. The problem is that the sound hole area is too weak, partly because of the sound hole, and partly because of a lack of bracing next to the sound hole. The guitar is essentially folding in half across this horizontal band. By running the X all the way to the UTB this is largely addressed. I also address this design flaw by using more robust sound hole reinforcement as you will see soon.

Two: I view the plates as membranes, and as the membrane becomes thinner and more flexible, it becomes possible for discrete areas of it to vibrate independently of the whole, usually at specific pitches. I call these local resonance nodes. I consider it of the utmost importance to distribute the top bracing so as to, as closely as possible, minimize the size of any unbraced top real estate. This allows me to permits the thinnest possible top w/o impairing the balance of the guitar through developing “wolf” notes. This is a super big deal for me.

With similar bracing concepts, smaller guitars can clearly have thinner tops compared to the same material in a larger guitar, according to this thinking. This 00 sized guitar top in medium/low density European spruce measures about .107”. I got there through feel, thinning the top until it was no longer able to produce a solid ring tone when tapped, held 1/4 of the length. This top has much greater cross grain stiffness than the Snakewood Carpathian in my preceding build, FYI, and it was more like .112”.

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Bruce Sexauer, luthier
http://mojoluthier.com

Here's the "new" rosette I mentioned earlier:

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Bruce Sexauer, luthier
http://mojoluthier.com

I'm certainly not experienced (or educated) enough to speak intelligently on the downstream effects of bracing changes, but I do find the discussions interesting. I like the idea of having the upper x legs support the upper bout and upper transverse brace structure to aid in keeping the block from rotating into the box. It seems to me that, in order to do that you have done 2 things: 1) "forward shifted" the x brace and 2) closed the X angle to some degree to allow it to still intersect with he bridge footprint. Do I have that right?

What are your thoughts about the effects of both of these changes? I recently designed bracing for a parlor guitar where I did both of those things to a lesser degree (the upper x legs do not go to the UTB). I just went by feel for what I felt like a reasonable amount of "openness" (for lack of a better word) I would get around the bridge and lower bout. I was happy with the end result but I don't really have any knowledge about what worked and what could have worked better. . .

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Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

If the X doesn’t get to the UTB, as in my layout, there is a “fold here” line I can see across the top. Another solution is a doubled UTB in an X. I have a photo somewhere and I’ll look.

My X does pass under the bridge ends, and so does the first tone bar.

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Bruce Sexauer, luthier
http://mojoluthier.com

Wow! That’s a lot of
Lines... god job getting them all to play nice:)


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Here's a shot of the inside of my 2018 "The Tree" 00 with a doubled X UTB:

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Bruce Sexauer, luthier
http://mojoluthier.com

I put my braces in rough in three tiers, shaping each tier completely before putting in the next. This allows me to get a better feel for the structure, including adding a bit of beef if I think I went too far on the tier before.

First tier in the deck:

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Bruce Sexauer, luthier
http://mojoluthier.com

All of my box construction up to glueing on the back is HHG. Some say the jury is still out about whether HHG is worth the trouble. I laugh at these lost should twice. First because it is little trouble, and second because . . . listen to any of my guitars from the last 25 years. It is the difference between dirty glass and clean glass. Yes, you can see through the window with dirty glass, but not with crystal clarity. Why get used to dirty windows?

This is the second tier of top braces in the deck:

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Bruce Sexauer, luthier
http://mojoluthier.com

Thanks for chronicling your progress on Couch Noodler #2 and for sharing insights into the reasoning behind your methods. I've stolen so much from dissecting your generous build threads that I should probably be paying you royalties. I preserve my amateur status by giving my guitars away as gifts, but if I ever sell one, I'll send you a bottle of something.

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George :-)

My email is my PayPal account . . . I'm doing okay, actually , thanks for saying so.

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Bruce Sexauer, luthier
http://mojoluthier.com

Very cool Bruce, great to see a build thread from a seasoned pro.
I really like the double-X UTB to add rigidity to a place that needs it.

Rob

Here is the third and final tier of top bracing in the deck.



And here is the final result:



I have found that 1/4" bracing on a thinner top transfers visible distortion on a gloss finished top in a way that slightly wider bracing does not. In the interest of a professional appearance, the narrowest of these are 9/32"

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Bruce Sexauer, luthier
http://mojoluthier.com

I do not use molds in my guitar body construction. I used to, but they seriously hamper concept growth (I continue to be about a better guitar, which is rarer in mature builders than I once thought)), and I dumped them about 25 years ago. There are a few tricks I've come up with to maintain symmetry and form.

I use a +/- 45' radius dish as a plantilla, which is modest by modern standards. Both end blocks meet the top at 90 degrees exactly. With my shallow dish this bisects the typical body taper nicely giving a good appearance to the body in profile. In a 25' dish, not so much. It is crucial to align the blocks perpendicular to the center line of the top. I leave a band of the inside of the blocks absolutely square to the center line drawn on them for the purpose of reference in glue up.





Because the dish is further below plane toward the center where the waist is than toward the edges where the blocks are, I use the jointer to put a step in the sides to make up for the difference. Counter-intuitively, smaller guitars have a somewhat deeper step than larger (wider) guitars!



The green tape marks the narrowest point in the waist, useful in the jointer cut and in the Fox Bender, another useful tool for achieving symmetry.

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Bruce Sexauer, luthier
http://mojoluthier.com

The first side is bent. This very dark BRW exuded more oil than I have previously experienced, and that's in something like 75 BRW builds. It blackened and looks charred, but sands off, thankfully. Here the side is held in its correct place by a few clamps. I have marked the ends to be trimmed to the center-line. When both are trimmed to length I will glue them to the blocks.

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Bruce Sexauer, luthier
http://mojoluthier.com

Looks like you all have a life! I will post anyway.

When the peone are fully set up, I will form the ribs to accept the back, then put in side ribbons, linings, and the back, which I have completed the bracing of while your gaze was averted.

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Bruce Sexauer, luthier
http://mojoluthier.com