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This is my 1st attempt at a 12-string. Here are some specs & pictures:

Back & sides: Australian Blackwood (RC Tonewoods)
Top: Engelmann Spruce (433 kg/m^3 density)
Neck: Honduran Mahogany
Bindings, Head Plate & Back Strap: Curly Koa
Tuners: Antique Acoustics (pricey) (Elderley)
Bridge: EIR
Saddle: Bone, with individual string compensation
Finish: French polish (CA pore fill)

Top thickness procedure: Starting with known top density, I used some of Al Carruth's data & ideas to calculate what top thickness I would use if this were a 6-string guitar (0.107"). I then used D'Addario data to obtain the string tensions for a 6-string (EFT16; 171.5 lb) & a 12-string (EJ38; 252.1 lb) setup. The cubed-root rule was then applied:

Thk-12 = Thk-6*(Tension-12/Tension-6)^0.333, or

Thk-12 = 0.107"*(252.1/171.5)^0.333 = 0.120".

I used an extra large heel block with an A-frame upper bout bracing (see pic). I also used extra bulky side braces to help keep the sides rigid & to add some mass to the sides.

It sounds great! (And is loud.)

Wow! very nicely done. Nice design, also I love the look of the Australian blackwood

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http://www.Harvestmoonguitars.com

Very nice! How big is it? How wide is the lower bout? It looks like a lot of work went into the saddle.

Regarding the A-frame braces, were they actually let in to the heel block, or were they butted to the heel block?

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Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

Nizzze!

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Pat

Incredible!

Beautiful guitar, Steve. How do you like the smaller body? Are you tuning to concert? Any significant changes to bracing in the lower bout?

Fwiw, when I built my OM 12 I just followed Taylors lead and bumped the top thickness from my usual 0.110 to 0.125 (but I also tune down). My old Martin 12 is 0.115 and has developed a bit of a belly.

Very nice!

It looks great. I have a nice set of blackwood and seeing yours makes me want to build with it.

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Steve Smith
"Music is what feelings sound like"

Wow! That's beautiful!

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Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

A touch of class there Steve. EIR FB too?
What's the scale length?
Be nice to see one pic of the whole guitar

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Thanks for the kind words & interest!

Answers to questions:

J De Rocher
The overall length is ~41" with a lower-bout width of 15".
The A-frame braces are glued into ~1.5" long channels in the heel block.
I used Liutaio Mottola's "Fretted Bridge Saddle Compensation Calculator" http://www.liutaiomottola.com/formulae/compensation.htm
to do the saddle compensation. Mottolo's calculator is set up to deal with 12-strings (or any number). Worked well & was easier than using the approach of putting a wire under each string & adjusting to set string length.

Freeman
The guitar is tuned to concert pitch, but I am using extra-light strings right now.
The lower-bout bracing was also beefed up a bit. The X-brace is 0.35" wide, 0.65" high, triangular profile, no scalloping.



The fretboard is ebony. I thought of using same materials for FB & bridge (either ebony or EIR), but I liked the look my classicals that use ebony FB with EIR bridge.
Scale length is a short scale 24.9"

Nothing more impressive that a big slot-head 12string head stock

very well made & beeeeeaaaauuuutiful also!
Mike

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Mike Collins

That's an interesting idea. I haven't seen that before, but like a lot of things, maybe it's have been done at some point in the past. I imagine it adds a significant amount of strength to that area. How do you make the channels?

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Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

Great miters on the end graft. What's your technique?

Beautiful instrument, not something you see everyday.

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It's not what you don't know that hurts you, it's what you do know that's wrong.

The A-frame is not an original idea with me. I learned about here on the OLF. The following link has some discussion & a nice pic from Buton LeGeyt.

viewtopic.php?f=10101&t=45037&hilit=carruth+a+frame&start=25


Thanks for noticing. Until this guitar, I had never been able to get all 4 miters on my end grafts, usually getting 3 acceptable ones & one that I was not proud of. Cutting the purflings attached to the bindings has never been a problem. Just used a small (~1.5 mm) chisel with a mirror-polished back. For the purflings on the end graft proper, I never had complete control of cutting miters using a chisel and the polished-mirror trick. (The purflings are glued to the end graft & installed as a unit.) For this guitar (oh, the shame of not using an edge tool ), I used my disc sander with a 45-deg fence & my binocular magnifier visor to see close up: Perfect control to get the miter at 45-deg & no wandering through the depth. Getting a perfectly vertical cut with a chisel was always a problem. Guess I should have built a jig. I recently saw that Stew-Mac has a drill press mounted binding cutter that might solve that problem.