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I have someone interested in a 12 string. 12 does not work in the search function so if there is someone who can point me in the right direction to the differences between a 6 and 12 string constuction it would be appreciated. It probably would be a Dreadnaught.

Thanks

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Here are the obvious structural differences:

String tension is higher: This will require a tad bit more mass in your top bracing. I go from 1/4" x 5/8 X-brace to 5/16" x 3/4" I increase my tone bars from 1/4" x 5/8" to 5/16" x 5/8". I use (3) 1/4" x 5/8" finger braces as opposed to 2. I increases my UT braces from 1/2" x 5/8" to 5/8" x 3/4". My top thickness on average increases from .115 to .120 this is all subject to deflection testing of materials but on average this is a good starting point.

The neck is wider and typically slightly deeper: I use 1 13/16" nut as apposed to a six string at 1 3/4". Depending on your desired string spacing the neck taper is wider. You need to be sure to account for this in your neck block. If you use a flanged FB extension on your neck blocks I suggest increasing the flange thickness by 1/16". This wider string spacing from E to e will mean that good X-brace support of the bridge wings is even more critical.

Peghead needs to be long enough and wide enough to properly place 6x6 tuners

For me these are the major changes made structurally

On my last 12, I reasoned that, since it was pulling about twice the tension, the top and bracing would need to be about twice as stiff. Since the stiffness of the top is proportional to the cube of it's thickness, I made the top 25% thicker (1.25^3=1.95). The same holds for the brace height, so I made the braces 25% taller, and a little wider to get some added gluing surface. Other than that, and a wider bridge plate, the top was the same as I always make. The neat thing is that, with twice the energy going in, and only 25% more weight, you get lots more power. That was the first guitar I've made that I could not sing over.

I use a wide saddle on 12s; about 3/16". When I first string it up I have the top of the saddle flat, and, of course, the strings buzz like mad. When I've got the action height and relief set up the way I want, I slip a short section of B string under one of the strings, move it around to find the proper break point, and mark it. When you've done them all you end up with two almost parallel lines at an angle across the saddle for the lower strings: the front one for the octaves and the rear one for the normal strings. Note that the octave G break point will usually be forward of the high E break point, so don't start with the saddle too far back.

Once I've esatablished the lines, I file a V-groove in the top of the bone between the two lines, leaving the lines alone. The front edge is filed back to the front line, and the rear edge is rounded up to the back line. Then the ridges can be notched out with a small round file where you don't want the string to hit: notch the front ridge so the normal string can vibrate freely stopped by the rear ridge, and file the rear ridge to allow the octave string to ride off the front. If you do this correctly you can have all of the strings play with good intonation all the way up, which goes a long way toward improving the sound of a 12. It looks like you meant it, too.

I did use a shorter scale length on that guitar, mostly to preserve the octave G strings at normal pitch. As usual, I also made it with a 12 fret neck, rather than 14. I _need_ to make another one of those.

Well, now, that all depends on the strings you are going to use, the pitch you are going to tune to, the scale length and what you want it to sound like. If you want "harpy" those thin tops (.120" ) may do it along with lite guage strings tuned to concert. I hate harpy. My last 12 used .068-.014", tuned to a C+ and with a 25.34" scale. Top was just under twice as thick as I make a 6 string, bracing 3/8" and a HUGE bridge plate. Tone is FAT and fabulous. Leadbelly would have loved it. Next one on the table has a top just a bit heavier than that, a 26.22" scale and aiming for .070-.014" tuned to B.

Good luck!

G'day Mark,

As a picture is worth a thousand words :



As a general rule , add around 20 % more than a 6 string to your braces and top thickness. I've added a third lower tone bar but after carving ,it didn't end up that big in profile.

I made this a thirteen fretter to help reduce torque on the neck . It's a 24.9 scale which reduces the amount of string pull and also aids in playability with the wider neck ( 1 7/8 " at the nut )

As Alan has pointed out , a wider saddle ( 5 mm.)so that you can intonate each individual string is well worth the effort . It's a joy to have a 12 string play in tune up the neck !
Note also in the below Pic. I have a shared 6 pin bridge . This saves weight and congestion around the bridge area. Here is a
link on a tutorial I did at the ANZLF forum on how to do this
http://www.anzlf.com/viewtopic.php?t=354





To add support to the headblock and help cope with the additional string pull I included an A Frame bracing system



The completed guitar is a great sounding 12 string . It's remained solid with no deformation in any areas and fantastic playability .

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CRAIG LAWRENCE of AUSTRALIA
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Here's the link for you about this guitar

viewtopic.php?f=10102&t=13971

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CRAIG LAWRENCE of AUSTRALIA
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Thank you for posting this valuable information. I very much appreciate your willingness to share with the rest of us.

Mark

_________________
Wisdom is justified by her children

Yup, a pix is worth a thousand words...

An earlier version...