Freeman wrote:
Cable, building a 12 string involves answering a whole bunch of questions, starting with tuning and string gauges, scale length, body size and bracing, and a few minor dimensions (nut width, bridge spacing, pin hole layout......).
I own a very nice old Martin D12-28 and have built two others, including an OM sized short scale and a long scale ladder braced (Stella clone).

I built the OM specifically because I wasn't satisfied with the balance on the dread - I am a finger style player and tune down a couple of steps - the dread was just too boomy. I spent quite a bit of time poking around in other 12's (Guilds, Taylors) before I build the OM - some of the design is based on my observations of these guitars. Here are the basic specs
I used a short Martin scale (24.9, in fact it is a Martin neck). If I was going to do it again I would go a little longer (25.4) because I do tune down to D using light gauge (0.010 - 0.042) strings. If you are going to tune to concert 24.9 should be fine.
Top is Sitka and is 0.125 thick (a little thicker than usual, Taylor does this). Bracing is 5/16 non scalloped with a third tone bar (again, Taylor uses three tone bars, my Martin dread is 5/16 but only two bars). Obviously a bigger bridge plate. The guitar is about 8 years old and the top has held up nicely. In contrast, my D12-28 is 35 years old and has developed a bit of a belly.
I did make the body a little bit deeper - that of course means that the guitar won't fit in a standard case and I had to have Cedar Creek make a custom case. Expensive and long delivery, the Stella needed one too.
I used a dovetail joint and the neck angle is fine, however I'm using bolt on necks on everything now (including the Stella clone) and would certainly do that on the next 12. I also used a Martin bridge with the octave pin holes closest to the saddle - you will find arguments for both configuration (note that Martin changed their minds with the Grand J-12 and put the primaries closest to the saddle). I used mini Grover tuners - they are fine but the big chrome washers that come with them are butt ugly (btw - I did make a drill jig for six tuners on a straight sided paddle head - if you want to use that shoot me a message).
Here are a couple more progress pictures




Am I happy with the guitar? Lets put it this way, the D12-28 almost never comes out of its case.
Freeman
Thankyou.. the info is great and you can't beat advice from someone who's been there and done it
I'm a few months of starting anything yet so have lots to think about
Freeman wrote:
Cable, building a 12 string involves answering a whole bunch of questions, starting with tuning and string gauges, scale length, body size and bracing, and a few minor dimensions (nut width, bridge spacing, pin hole layout......).
I own a very nice old Martin D12-28 and have built two others, including an OM sized short scale and a long scale ladder braced (Stella clone).

I built the OM specifically because I wasn't satisfied with the balance on the dread - I am a finger style player and tune down a couple of steps - the dread was just too boomy. I spent quite a bit of time poking around in other 12's (Guilds, Taylors) before I build the OM - some of the design is based on my observations of these guitars. Here are the basic specs
I used a short Martin scale (24.9, in fact it is a Martin neck). If I was going to do it again I would go a little longer (25.4) because I do tune down to D using light gauge (0.010 - 0.042) strings. If you are going to tune to concert 24.9 should be fine.
Top is Sitka and is 0.125 thick (a little thicker than usual, Taylor does this). Bracing is 5/16 non scalloped with a third tone bar (again, Taylor uses three tone bars, my Martin dread is 5/16 but only two bars). Obviously a bigger bridge plate. The guitar is about 8 years old and the top has held up nicely. In contrast, my D12-28 is 35 years old and has developed a bit of a belly.
I did make the body a little bit deeper - that of course means that the guitar won't fit in a standard case and I had to have Cedar Creek make a custom case. Expensive and long delivery, the Stella needed one too.
I used a dovetail joint and the neck angle is fine, however I'm using bolt on necks on everything now (including the Stella clone) and would certainly do that on the next 12. I also used a Martin bridge with the octave pin holes closest to the saddle - you will find arguments for both configuration (note that Martin changed their minds with the Grand J-12 and put the primaries closest to the saddle). I used mini Grover tuners - they are fine but the big chrome washers that come with them are butt ugly (btw - I did make a drill jig for six tuners on a straight sided paddle head - if you want to use that shoot me a message).
Here are a couple more progress pictures




Am I happy with the guitar? Lets put it this way, the D12-28 almost never comes out of its case.