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Hi all,

I've got a 12 string acoustic in design phase right now -- never made one before, nor even played one. I've read quite a bit on this forum about top thickness, bracing, and so forth, including this tute from Paul Woolson http://www.luthiersforum.com/forum/viewtopic.php?p=193775#p193775 which takes all the mystery about string spacing on the nut end of things.

But I haven't found anything about spacing the strings at the saddle. Do the strings in each course run parallel, or do they spread as they go down the neck? If so, does the spacing increase at the same rate that the strings separate on a six-string build?

I'd like to start cutting wood in the next week or so, and doing so without knowing this particular fact would be foolish .

--Paul

I just finished one the other day. The courses widen slightly going up. I don't like it. I recommend trying to keep them even with each other.

Maybe you can find one you like the feel of and copy it...

While I also plan 12 string spacing using the Stewmac rule, as described by Paul, I feel his pair spacings are far too close at the treble side. Assuming you want to use a typical 12-pin bridge, your pair spacings will need to widen from nut to saddle, to clear bridge pins. You should find this blog entry by William Cumpiano of interest:
http://dolcecano.blogspot.com/2009_03_0 ... 4614424435

Some folks get closer pair spacings at the saddle by putting 2 strings on each of 6 pins. Personally, I dislike that approach.

BTW, nut width on a 12 makes a huge difference for most players, and preferences vary a lot. Typical nut with is 1-7/8", but I find that feels like a cricket bat. For me, reducing to 1-13/16 makes all the difference in how a 12-string feels.

Paul, since you are still in the "design stage" this is a very good time to think thru all of the aspects of your guitar including scale length and the tunings and string gauges that you will use. Assuming that you will string it more or less "normally" then the primary string will be the odd numbered ones. At the nut end I like spacing between courses of about 0.090 to 0.095 and I also use the StewMac ruler to get this. I mark the outside strings based on the way I play (I thumb fret so I like the 12th a little closer to the edge) then I mark the 11th string 0.095 in from the 12th. Use the SM ruler to lay out the primaries (odd numbered strings), put the octaves 0.090 or so to the outside. It simple and it give a spacing that feels right.

Also at the nut you need to decide how deep to cut the slots - most people probably prefer the bottoms of the slots to approach the zero fret line (ie the tops of the octaves are lower than the primaries) but if you play slide like I do you might want the tops more or less level. Again, style of play will help you decide.

At the bridge your string spacing is more or less determined by pin layout (assuming a pinned bridge). You can slot and ramp the pin holes which can control spacing a little but the back strings simply will run into the heads of the front pins. About the closest you can get is 0.095 which is what I like, there are players like Chris Proctor that purposely space them farther apart so he can play each string of each course separately. I shoot for having basically the same separation, maybe widening slightly, from nut to bridge (of course the overall spacing is greater at the saddle). One little design issue here is where to put the primaries or the octaves closest to the saddle - you will see both (and there are arguments for both). Martin always put the octaves closest but for some reason on the Grand J they switched them. Having the narrower octaves behind the primaries does let you space them slightly closer.

Most people don't slot the saddle on a pinned bridge but with a tailpiece you do - that can be used to set spacing (and height). Another little trick of setting up a 12 is trying to compensate each string - it can be done but your saddle will end up looking like a rip saw blade.

I'll throw out a couple more thoughts about designing a 12 string. First, the tension is not double that of a sixer but more like 150% - calculate your bracing accordingly. Second, many people do like to tune down one or more semi tones - again, calculate scale length, strings, bracing, etc based on that. Worth while to play as many as you can and poke around inside to see how they are built.

Here are my three - an old Martin dread (short scale, usually tuned to D or D#), OM (long scale, always tuned to D), very long scale ladder braced ( strung with cables and tuned to C)

this is a falcate braced 12 string , using a 6 pin bridge and fully compensated nut and saddle, I used a 1 7/8 nut, string spacing is drawn out on a cad program with spacing based on string diameters and such, I would have to look back to my files to see the numbers I used, however as you can see I have some room to bring the low e and a octaves a little closer and too agree that a 1 13/16 nut would feel better..just some ideas to throw around. There is a good tutorial on the 6 pin method over at the Australian New Zealand forum, and of course some great stuff in the Gore Gillet books on intonation. I use a small cnc to machine the nuts but Trevor shows how to make a great jig to use in a drill press to cut the nuts, also there is some great stuff here by Al Caruth on intonating a 12 string using a string jig, which I also used to get the actual string compensation at the nut and saddle, very easy to build .

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MK5acoustics.com

Here's my first try...

The nut is pretty good. I will make a test jig next time I think, to test the boundaries of how close you can get the strings together as a pair. As well, I'm going to change the headstock to bring the tuners a mil farther apart in each direction. They don't hit the posts, but pretty close...

Here's the pin spacing at the bridge...
It's ok, but I would like them closer together, as sometime when playing, your fingers divide the chorus' when pressing down. More like the D and G sets that I'm pinching together.

As you can see, there is just enough room to squeeze past the pins to come closer to where I want them...

This would be a great area to experiment with a pinned/Pinless hybrid, or one of those bridges where the ere is a metal pin sticking up that the hole in the ball end slips over...

Anyway, next time I will use the same relationship between courses at the bridge, and just space the pairs correspondingly wider. I had that feeling when I layer it out, but it was copied directly from my Martin so I though it'd be alright...putting the octave strings behind the primaries makes a lot of sense, wish is considered that...

Would it work to slot the bridge so that the pairs are the spacing you want? Does putting a slight side load on the bridge slot damage it?

Ed

Thanks, all, for the good advise. Wes -- that compensated nut is exceptionally cool looking! I'm going to have to invest in Gore Gillet tomes at some point.

What I got out of the responses (about string course spacing at the saddle) is to keep them as close to parallel as possible, given the constraint of the pin widths, which is something I didn't think of. I saw the two-strings in one pin discussion over on the Ausie site a couple of years ago. That would solve the problem of pin interference. But I don't like it -- entirely because of aesthetic reasons.

Here is what the plan calls for so far on the neck.
1) Short scale (24.5") 12 fret neck.
2) 10" Radius. I am getting arthritic on my fretting hand, so I need it to play as easily as possible (small radius, low action).
3) I'm going to go with a 1 7/8 nut. It will be kind of wide, i realize, but I want to have some wiggle room in case the strings start hitting each other.
4) Primary strings will be odd-numbered.
5) I don't use a slide, so the bottoms of the strings in each course will be co-planer.
6) I'll put the skinny string pins on the back of the bridge -- I thought that was a brilliant comment, by the way.

I'm going to tune the thing to D#, again because to my hand strength is compromised by the arthritis.

Again, thanks for the great advise. When I get into the shop, I'll start posting pictures.

--Paul

Ruby,

Do you mean slotting the saddle? Don't see that as a problem, I've done it before here and there.

Paul,

I'd try to do a mock up for your 10' radius 1 7/8" nut. Not saying it wouldn't work, but I'd be worried about such a tight radius across such a long span, but have no experience with that. Just that it's something I've never encountered, and it could be with reason, or...not. Dunno.

I also think that being diligent with your string spacing at the nut should make a 1 13/16" nut entirely possible. That's my next experiment.

And, furthermore...the Gore/Gilet books are an extremely good investment. They might not feel as sexy or seem as important as buying wood and tools, but they will certainly help you get much more out of the aforementioned items. Just sayin'...

Paul, I like your kind of talking...that 1-7/8" nut sounds fine. I liked to stay around 1-7/8" to 2". You might consider 1-15/16" depending on whether you like a little more space between courses.
Woolson's spacing is just right, the 24-1/2" scale tuned down. I have built a few 23" 12's and here is the only problem. As the strings get shorter in scale, the tuning drops and the strings get heavier because you are tuning down, you start running into tuner problems. It's a good thing you are in the planning stage as it is something to consider. I would get the highest gear ratio you can find.
On the 23", I had to resort to taking 2 sets of Stay-Tites and buy 2 sets of F mandolin tuners, cut them like this...



...and switch out the long shafts with Stay-Tite shafts. I ended up with a sets that had an 18/1 gear ratio. At that short scale length, and tuned to B with HEAVY strings, it was still a little twitchy to tune.
At 24-1/2" you might be OK, but you should do a string setup on some junk boards to try your pick of tuners and see how they work. Just mount some on a board and use brads for a saddle. Stick some kind of nut on there and see how the strings tune. Something else to consider is the mandolin spacing is closer than guitar standard spacing. Nice thing about the Stay-Tites is they work fairly well and parts are easy to get. It played like a dream and I hardly moved my elbow at all. I could tuck it right next to my side. Thirdly, you can make the peghead smaller and it doesn't look like a canoe oar on the end of a guitar.

Hey, what a blast from the past.

That guitar has been 80% built, and holding, for the past couple of years. Life, and birthday guitars for grandchildren have gotten in the way.

Once I get the last birthday present finished (carving the neck tonight) I'll pull the 12 string out of the case and finish it up.

--Paul

Well, my fault. Looks like I got into the other thread, slipped over to this one and forgot where I was. Hope your 12 works out...