Symmetrical X-braced OM 12-string

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Stray Feathers
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Symmetrical X-braced OM 12-string

Post by Stray Feathers »

While number 3 waits for better weather for finishing (outdoors, under cover) I have started number 4, a 12-string. I was considering a Larrivée L-body style (it worked for Stan Rogers . . . ) but realized that was about the size of a Gibson J-45 - bigger than I wanted. I went around in circles and ended up using the same Jonathan Kinkead-designed OM plans I have used on my first three builds. This one will be about 1/4" deeper, though. I have read a lot here and elsewhere that luthiers often don't scallop the bracing on a 12-string, because there is so much built-in volume with twice as many strings. I also have a Larrivée rosewood dreadnought which is a lovely guitar, and I have wanted to try a guitar braced the same way, for reasons often expressed by others in various places. I thought maybe the 12 would be a safe place to try the symmetrical X-bracing in a smaller 12 string. This one is Sitka Spruce over Black Walnut and will have a walnut neck.

A couple of points on the photos:

The side struts are as recommended by Kinkead, except I added one more on each side, in part because I have a little rippling in the sides. I also found older threads here on KGF in which builders recommended notching the struts into the kerfing to avoid a stress point. That made sense to me; Kinkead does not do this in his book.

The top bracing is based on Larrivée, but I arched or rounded them somewhat. He uses flat finger braces, tucked under the kerfing. Kinkead and a plan I have from Cumpiano use vertical braces which end before the kerfing. A photo I have seen of bracing by Grit Laskin, a Larrivée protegé, is very similar to what I have done, with finger braces vertical and tucked under the kerfing. Bridge plate is a little larger. At this point, with so many variables, it will be impossible to know which if any of those decisions will have made any improvement. But it should be fun to see what happens. At the moment I am very pleased with the way the tap tone still comes through after all the bracing. Bruce W.
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tippie53
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Re: Symmetrical X-braced OM 12-string

Post by tippie53 »

nice clean work
John Hall
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phavriluk
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Re: Symmetrical X-braced OM 12-string

Post by phavriluk »

Appreciate seeing a 12-string project. Quite some bridge plate on this one. And I'd been musing about the tone bar distribution shown on this one as a means to get as much strength out of the tone bars while respecting the weight schedule.

Thanks for sharing.
peter havriluk
Stray Feathers
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Re: Symmetrical X-braced OM 12-string

Post by Stray Feathers »

Peter, I had a hard time finding any detailed guidance on this type of bracing, and especially for a 12-string, so I am going a lot by intuition, or that old acronym, TLAR - "That Looks About Right" . . . As for the bridge plate, the only advice I could find for 12-strings was to make it "a little bigger". So it is about 1/4" taller, but the surface area is quite a bit more, because the corner on the treble end is not cut off by the Martin-style tone bars usually used. It would be nice to have the luxury of doing another with lighter bracing and bridge plate to compare; I'll see what the future holds.

I don't know if I am permitted to post a link to American Lutherie magazine - in issue 123 there is the photo of the Grit Laskin bracing I referred to. I do not have the whole article, just the teaser from the web site: https://luth.org/journal/american-luthe ... fall-2015/

Bruce W.
phavriluk
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Re: Symmetrical X-braced OM 12-string

Post by phavriluk »

Bruce, I understand TLAR design procedures. I've got four scratchbuilt guitars as evidence. And a 12-string in the works, which causes me to pay careful attention to what you've done.

I'll stay tuned, I'm sure I'll learn more good stuff.
peter havriluk
ruby@magpage.com
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Re: Symmetrical X-braced OM 12-string

Post by ruby@magpage.com »

The picture in the teaser is interesting. It is easy to see that the UTB is at quite and angle, and I wonder why? But not so easy to see if the tone bars are at an angle or not. But then, why would it be called "symmetrical" if they were? You're doing a very nice job,

Ed
Ed M
Stray Feathers
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Re: Symmetrical X-braced OM 12-string

Post by Stray Feathers »

Ed, it looks like the brace is angled because of the cutaway? I've never done a cutaway so don't know how it is usually done. (I just searched on line and there is an image of the bracing on a Larrivée cutaway, and the UTB is perpendicular to the centre line, and stops short of the cutaway.) The tone bars appear to be perpendicular to the centre line on Larrivées, but you're right, with the angle of the photo, Laskin could angle those braces. and they wouldn't be technically symmetrical. And thanks for the compliment; I'm still new at this and work slowly, and just like to do a clean job, even if nobody sees it. A friend is fond of saying, "If you don't have time to do it right, when will you have time to do it over?"

I found another symmetrically braced guitar on this blog. I did not want to post the image without acknowledging copyright, so you will have to scroll down a fair bit to find it:

https://acornhouseworkshop.com/in-the-workshop/page/3/

Bruce W.
Stray Feathers
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Re: Symmetrical X-braced OM 12-string

Post by Stray Feathers »

I got the body of this guitar glued together fairly early in the pandemic shutdown, but not without event. I think I have been building these things with too much curve in the back, and this time found I had a bulge over the neck block. I gritted my teeth and applied heat and spatulas to free the glue joint there (had to take it back about 8 - 10 inches along the back). I cut and filed and sanded it down to a fair curve and reglued it, with a lesson learned along the way. With other projects on the go, this one sat for a while, but I have now routed the mortise for the neck tenon. This is my fourth guitar, and I don't know why I have no photos or description of how I did this, so I documented the method I used on this one. The body sits in a cradle I made for use with a binding jig, with the front support removed. The tailblock end of the guitar is clamped to keep it down. The jig (made for a Bosch Colt router) is clamped to the guitar body with a wedge-shaped caul underneath to provide more stable purchase for the clamps. The cradle base is clamped to the work table. It worked quite well. I used the same jig to rout mortises on three tenor ukuleles, but could not use the cradle. Instead I clamped the jig to the body, then clamped the clamps to the table so the body was vertical, something like the illustration in Cumpiano/Natelson. I reset the plywood stop held by red clamps to a different position for the smaller bodies.
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Stray Feathers
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Re: Symmetrical X-braced OM 12-string

Post by Stray Feathers »

I have spent a lot of time trying to figure out the best way to lay out the peghead for this 12-string. Some makers use a system where some strings must bend to get past other tuner posts; some say this should be avoided. I had bought Golden Age mini tuners when Stew Mac had them on sale, so was hoping to use them. The Gibson/Epiphone design seems to work, but I was hoping to keep my tapered headstock design. In the end I went with a 1 13/16 nut (slightly narrow but that may be good for my small hands), and that gave a little more string room. The peghead is probably a little on the heavy side, but nothing could be as big as the peghead on the Eko I had in the 70s . . .

I decided to use a piece of found wenge for the overlay. I had difficulty getting it to stay put when gluing it, and did not use a wide enough caul, so the edges curled up - dang! I removed it with a power planer, hand plane, chisel, and sanding, and cut another one. This one I positioned with micro-pins as I learned to do with fingerboards. That gave me more time to set up clamps and cauls properly, and it went okay.
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Stray Feathers
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Re: Symmetrical X-braced OM 12-string

Post by Stray Feathers »

Here is the 12-string body and the roughly-shaped neck with wenge headstock overlay. The neck joint has been fitted pretty well so I will only have to do final shaping on the neck. I found I had to determine the headstock shape, and do the curved volute, in order to proceed with neck shaping. Along the way, I cut myself a bit short on stacked heel pieces to have enough tenon in the body, so had to move the nut just ahead of the 15º break, Martin style. Have not done that before. I may shorten the headstock when I lay out the tuner positions. I have not done the MOP inlay of my "W" logo yet. Next after that is an ebony fingerboard.
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