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Hi there,
Apologies if this topic has been covered, but I couldn’t find anything.

I am just about to embark on my first 12 string guitar build.However bridge design is proving to be a bit of a head scratcher. How does one achieve the desired gap between string courses? given the radius of the bridge pin head.
Also what would be a safe distance between the two rows of pins?

Anyone able to shed any light on the topic, or directions for any good sources of reading much appreciated.

If you "slot" your bridges you can angle the slots and do 2 per hole and only use a single row of pins. Some violin tail pieces did it this way, but with the adoption of fine tuners on multiple strings this type of tail piece fell out of favor. If you go with two rows of holes you can slot the front row off to one side to allow a little tighter string spacing while still missing the bridge pin with the back row of strings.
String spacing between strings in a course is generally a 1/10th of an inch +/-.

I was also going to suggest what Clay recommended - 2 strings per hole, 6 hole bridge. It allows a smaller bridge, and half as many holes to drill in your top.
There is a really useful tutorial on how to do it by Craig Lawrence on the ANZLF.
http://www.anzlf.com/viewtopic.php?f=5&t=354

Others have covered your main question - slot and ramp the path you want the string to take. But there are several other questions to ask - first how are you going to string it ("normal" with the octaves on the even number strings or ala Rickenbacker with the octaves on the odd). Next, do you want the octave pins closest to the saddle or the primaries? If you go with the two string per pin design you make it slightly more difficult to change a broken string and you need to be really careful about how the balls lay on the bridge plate. Last option is to go with a tail piece and slot the saddle to position the courses. I have also see 12 strings with pinless bridges (Ovations) but I think that is a really bad idea.

When you slot and ramp your bridge think about how you play. Most 12 string players pluck both strings of a course simultaneously but a few (Chris Proctor comes to mind) can play individual strings. That might affect your spacing.

The two holes per string works out nicely and is easier than one might imagine. I followed the instructions from craig on the anzlf site that Mark suggested. http://www.anzlf.com/viewtopic.php?f=5&t=354

I have a full blog of my 12 string that show some of the steps making the bridge

http://harvestmoonguitars.com/angel12string1.htm

.

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http://www.Harvestmoonguitars.com

It is great that John jumped in there. His blog should be a big help to you. It reminded me of one thing he does, but did not explicitly mention - a wide saddle, to allow more wriggle room in setting the intonation for all those strings.

Thanks guys, this is all excellent food for thought!
I have been toying with the wide saddle idea for a while too, what constitutes a wide saddle now though, anything over 1/8”?
I’ll have a good read of that Craig Lawrence thread!

You need about 3/16" to accommodate the compensation for both the 'normal' and 'octave' strings. The octave G will need almost no compensation, so don't make the slot too far back, and don't angle it too much, or you'll have problems getting both the high E and octave G right. The E and B strings will want a high point with with the normal sort of slope, but the octave G will need much less compensation than the regular string. This disparity continues all the way down from there.

I find it easiest to set the thing up with a flat topped saddle, and use the 'B string trick' to set the compensation from there. Us a short length of B string passed under each string to raise it up off the saddle top and find the break point that will give the correct intonation at the 12th fret (I like to use the open string and the fretted note at the 12th, rather than the overtone). You will end up with two lines of point along the top of the saddle; the usual one near the back for the regular strings, and one in front of that at a bit less of an angle for the octaves.

I remove the saddle, and file the top to a peaked cross section, like this:
/\/\.
I use a triangle file to make the trough, round off the back edge of the rear peak, and make the front edge pretty steep. Then, when I put the strings on, I use a small round file to notch out whichever peak is not needed for that string. This ends up looking like you meant it, and is much simpler than trying to get a single ridge that meanders across the top of the saddle and ends up in the right place.

On my last 12 I also did nut compensation. I had to move the nut forward by about 4 mm, iirc: the player wanted it set up for open G tuning at standard pitch. Then I used a Dremel to notch back to the appropriate break point. The result was that no note on it, regular or octave string, was more than 3 cents off at any fret all the way up. It didn't have the characteristic 'crunchy' sound that we associate with 12s, but it was a real pleasure to play up the neck. I imagine you could dial in some small amount of crunch if you wanted without doing too much violence to the intonation, but the player really liked it.

A lot if experience and wisdom packed into that one post, Alan. I never would have come up with that “twin peaks” approach, or the “b-string trick”. Thanks for sharing them. I do tend to end up with a break line that meanders along the top of the saddle like a drunkard on his way to bed. I am struggling with this on a current build which is a multiscale 7-string, so I will put your techniques into action.

It is an interesting question whether the tuning and intonation on a twelve string can actually be too close to perfect? The characteristic sound of any instrument with unison pairs of strings derives from the fact that they are not exactly the same - just like a choir of voices. When they made those old Stella and Gibson 12s that we all grew up listening to there was no-one at the factory perfecting the intonation. Two notes that are almost in harmony with each other is part of the signature sound.

Here a a couple of mine...

[IMG]https://uploads.tapatalk-cdn.com/
20190831/9af17b42a85d6813254ed916d5060ee9.jpg[/IMG]


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