Here's an experimental project I'll share... I've been posting about this one over on the UMGF because I needed help finding a source for CNC cut replacement necks. There are some really sharp luthiers who hang out there, a couple I know a little bit.
The backstory first; I've had this old Martin 12-string for almost twenty years, a 1969 D-12-20. Style 20 is almost indistinguishable from Styles 19 and 18... a little bit of purfling and binding is about all. If they made anything other than 12-string Dreadnoughts in Style 20, I've never seen one. So I got this beautiful old guitar... can count on the fingers of one hand the times its its gotten used. I remember recording with it a couple times, when we needed a jangly rhythm guitar. The acoustic folk band I was in had a little more use for it. I put it up for sale, along with an old Martin mandolin at the local music store I do bass repair/setup for. The mandolin sold, this guitar just sat. So I picked it up last weekend, and started thinking...
It desperately needs a neck reset. Just to keep it playable, the bridge has been shaved almost flat. Other than that, it's pretty clean. No cracks, couple dings, amazing mahogany sides and back, kinda' ordinary spruce top, rosewood (probably Brazilian in '69) fingerboard, and what's left of the bridge.
I talked to my buddy and mentor Ward Elliott about the neck reset, and sure, he'd help me with that... but I started wondering, what if this guitar was a 6-string instead of a 12...? Now we're back to the front. I found a source for 12-fret Dreadnought necks from a CNC machine, that come with the dovetail cut, even a truss-rod channel routed and headstock slots cut. That was a big hurdle, I can handle things from there in my own shop. So I put that old Martin on the workbench and started measuring things. It was about that time I came to the realization, Martin 12-strings, even though they are D-size, are short-scale. Oops! That changes everything. Instead of 25.34", these came with 24.84". That moves the saddle a half-inch back. Not impossible to deal with, considering the bridge footprint is oversized anyway.
I took some sage advice and spent the rest of the afternoon doing a temporary conversion, just to see -not to put too fine a point on it- how will it sound with half the strings it was designed for. In addition to the shorter scale, these things were incredibly overbuilt, inside and out, to withstand the extra tension of all those strings. The top soundboard has a third tone bar (brace) glued laterally right behind the huge rosewood bridgeplate. Ward joked, when I sent him a picture, there was enough lumber for two guitars in there! I eased the original bone nut out of its slot, and made a new one with a scrap of ebony. I removed the old 6-on-a-plate machines from each side of the headstock and mounted an old set of nickel Waverly W-16's I had stashed away, skipping every other hole; perfect fit. Looks a little bit funny with that long headstock, but it worked. Getting the string spacing approximated at the bridge was harder. I ended up filing 'keeper' slots in the saddle to hold the strings where they needed to be, then staggered the mounting between the doubled rows of bridge pins. Again, looks goofy, but works!
Finally, strung it up. I've been passing it around for a few guitar players to test-drive. I'll say this; it should not sound like it does. I am quite surprised at how loud it is. The tone is a little weird. I think some of that is because the neck angle is so shallow and the saddle is so low that there's almost no break angle over it. That's a pretty big deal on an acoustic guitar, or really any stringed thing... that downward pressure has so much to do transfer of vibe from string to top. So I think that improves vastly with a neck reset.
I think it's worth doing, so I think we're going to convert it to a 6-string. There are a few things to decide, maybe a short-scale, maybe a long-scale. We'll make a new bridge of course, that will be oversized, but drilled for 6 pins. The bridgeplate will have to be plugged and re-drilled. But we'll save the original 12-string neck intact for a future retrofit. Nothing done that can't be undone. I already have everything else for the project.
Here's a few pictures:
