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12 string neck reset and bridge repair advice
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=41961		 Page 1 of 1
Author:  RLHope [ Sun Nov 17, 2013 9:09 pm ]
Post subject:  12 string neck reset and bridge repair advice
A buddy of mine brought me a 1970's vintage Alvarez 12 string that is in bad need of a neck reset. Should the neck angle be greater for a 12 string to compensate for the added stress or the same as a 6 string (I follow guidelines in Cumpiaonos book, straight edge with 1/16 - 1/8 gap above bridge). Currently the neck without strings has a 90 degree or even negative angle (angled towards top vs. away).


When I got it it also had this bridge repair that had been done in the past (see picture) Any advice on how to "repair this repair" without creating a whole new bridge? As this insert is through the bridge to the soundboard I suspect the sound was extremely dampened (strings were off when I got it so I never heard it).

Not a real expensive guitar, but worth practicing a neck reset on.
Author:  Chris Pile [ Mon Nov 18, 2013 12:19 am ]
Post subject:  Re: 12 string neck reset and bridge repair advice
That bridge may be stock....
Author:  Freeman [ Mon Nov 18, 2013 3:49 pm ]
Post subject:  Re: 12 string neck reset and bridge repair advice
I've built a couple of 12 strings and have an old Martin which has been reset. I shoot for the "usual" straightedge on or just above the bridge, and about 1/8 inch of saddle sticking out with acceptable action. Remember that depending on strings and tuning, a 12 has about 50 percent more tension (not double as many think) and a correctly built one will have slightly beefier bracing and maybe a thicker top plate.

You will need to make a new saddle after the reset and one advantage of a wider slot is that you have more room to work your compensation - making a new bridge or filling and rerouting that one my be the best solutions.
Author:  RLHope [ Mon Nov 18, 2013 9:26 pm ]
Post subject:  Re: 12 string neck reset and bridge repair advice
Thanks for all the responses. In looking at the bridge closer I think Chris may be right in that it is stock, no real "evidence" of this being modified other than the metal insert looking strange.

For the reset, may be a mute point as I contacted Alvarez to get some details and they indicated this is most likely a dovetail joint secured with Epoxy. Don't know how to get that apart without a blow torch unless any ideas out there. May consider making a whole new fingerboard that is tapered to fix the problem like a classical. I need to get around 1/8" rise at the 12 fret to have the straightedge at the bridge height.
Author:  Freeman [ Mon Nov 18, 2013 9:42 pm ]
Post subject:  Re: 12 string neck reset and bridge repair advice
RLHope wrote:
For the reset, may be a mute point as I contacted Alvarez to get some details and they indicated this is most likely a dovetail joint secured with Epoxy. Don't know how to get that apart without a blow torch unless any ideas out there. May consider making a whole new fingerboard that is tapered to fix the problem like a classical. I need to get around 1/8" rise at the 12 fret to have the straightedge at the bridge height.


That is pretty common for Yamahas from that period - the solution if you can't get the neck off with steam is often to saw it off and make a butted bolt on. I have a 1969 Yamie and have done that - its kind of brutal but does allow you to save these guitars. I've got some pictures if you decide to go that route.

On another forum someone suggested injecting some sort of strong solvent into the neck joint to soften the epoxy - has anyone tried this? If so what did you use and did it work? I would be very worried about damage to finish but the sawn off neck also has the potential of damaging finish.
Author:  RLHope [ Mon Nov 18, 2013 10:36 pm ]
Post subject:  Re: 12 string neck reset and bridge repair advice
Yeah Freeman, send me some pics as I would like to see the bolted butt setup. All the ones I have made (3+) have a bolted mortise and tenon so getting the neck set was pretty straight forward. Not sure how I would get the location secure without the tenon as that typically holds the position for the neck and the bolts just pull it snug.

When you sawed it off did you have to move the bridge to compensate for the 1/8" loss of neck length or did you glue on an extension to the neck to get the length right?

Brutal or not, this guitar is not being played now so any work is better than becoming kindling.
Author:  Terence Kennedy [ Mon Nov 18, 2013 11:44 pm ]
Post subject:  Re: 12 string neck reset and bridge repair advice
I did a reset on a 70's Alverez OM four years ago. Took an X-Ray first and it looked a little strange with not a lot of space for a needle. Something didn't look right.

Image

Image

I forged ahead anyway with lots of steam and not much luck. Finally sawed off the fretboard at 14 and saw that the whole thing was filled with epoxy including the area around the extension of the truss rod.

Image

More steam under direct vision and lots of "gentle persuasion" and it came out in one big sticky mess.

Image

Image

I converted it to a bolt on and did a lot of other work on it and it turned out to be a great sounding guitar, I was amazed.

Image

Image

I have not seen it in several years but no bad news so far. These days I would have made a little beefier fretboard tenon. Hope this helps.
Author:  RLHope [ Tue Nov 19, 2013 7:15 am ]
Post subject:  Re: 12 string neck reset and bridge repair advice
That is really cool! I need to ask my wife for an Xray machine for Christmas, never even thought about having one of those in the shop!

Seriously though, thanks for the pictures and explanation, that helps a ton. I can see it is a bolt on but not a true butt joint since you still had some dovetail to position it. The last picture looks like an "old" fretboard from behind, but you sawed the original. Did you make a new one or just glued the old one back since it was past the playing area and covered it up with the fret?
Author:  Terence Kennedy [ Tue Nov 19, 2013 8:26 am ]
Post subject:  Re: 12 string neck reset and bridge repair advice
RLHope wrote:
That is really cool! I need to ask my wife for an Xray machine for Christmas, never even thought about having one of those in the shop!

Seriously though, thanks for the pictures and explanation, that helps a ton. I can see it is a bolt on but not a true butt joint since you still had some dovetail to position it. The last picture looks like an "old" fretboard from behind, but you sawed the original. Did you make a new one or just glued the old one back since it was past the playing area and covered it up with the fret?


I re-glued the original extension and that worked fine. Glued the original fret back in as well. Good luck!
Author:  Freeman [ Tue Nov 19, 2013 11:48 am ]
Post subject:  Re: 12 string neck reset and bridge repair advice
Here are two threads from a different forum. This guy claims to have done several (or many)

http://www.harmonycentral.com/t5/Acoust ... 41#M540557

and here is my little FG-150

http://www.harmonycentral.com/t5/Acoust ... ue#M571501

I did not compensate for the saw kerf by doing anything at the bridge other than making a new saddle for it with the usual B string compensation. I frankly can't say how bad the intonation is - its just nice to be able to play it again.

On my new 12 strings I do like to make an extra wide saddle slot and compensate each string of each course individually - the saddle looks a bit like a rip saw blade but they more or less play in tune up the neck.
Author:  RLHope [ Sat Nov 23, 2013 9:11 pm ]
Post subject:  Re: 12 string neck reset and bridge repair advice
Thanks for all the advice and pics. Used the same methods proposed and it worked fine. Here is a pic of the joint after removal
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