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Greetings, esteemed lords of lutherie

Allow me to introduce myself. I am a retired engineer who took up learning to play the guitar only two years ago. I now own two acoustic, one classical and one electric guitar. I enjoy learning to play. In addition to the joy I get by learning to play, I also take a more than casual interest in the mechanics and physics of the guitar and enjoy “tinkering” with minor repairs and seeking setup perfection (on my own instruments only!) I have dared to enter your sanctum sanctorum in hopes of finding a reliable answer to, what may turn out to be a stupid question (in which case I will apologise for wasting your time).

I recently purchased a Washburn D25S 12/N guitar. According to the serial number this 12-string modern was manufactured in 1986. It is in very good condition. I replaced all of the Grover tuners as half of them had been damaged by over-torquing. All bracing is secure and there is no evidence of cracking anywhere. The bridge is secure and the saddle appears to be original and well shaped.. The neck is straight and the truss rod is effective. I have fitted Ernie Ball 80/20 Bronze 09-46 strings.

Now to my question. When tuned to “standard” (EADGBE) there is a noticeable bulge in the top of the top surface of the lower bout directly below the bridge. This is obviously caused by the string tension to the bridge being transferred to the spruce top. Question: is there a way to determine how much deflection (bulge) is acceptable (or “too much”) for a guitar of this make/age? I have since tuned it down one whole step (DGCFAD) to reduce the tension and play using a capo on the 2nd fret, however I would prefer to be able to play with standard tuning.

I know it’s neither a valuable, nor “junk” guitar, but I would like to get a few years use without destroying it. Any advice or guidance you can provide would be highly appreciated!

Respectfully, Ryan

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Definitely recommend dropping the tuning. A step down makes for easier transitions. (When everyone is in "D," you would play "E." Twelve strings and capos are not always a happy marriage. If you have a capo that works well, then by all means use it. Best wishes on your guitar journey.

Thank you for your prompt response! Dropping down is no doubt the safe approach and I have a Schubb 12string capo that works alright. Still, I would feel more comfortable playing in standard tuning (old dogs are slow to learn new tricks). From the purely structural aspect, can you give me any guidance on how much bulge would be considered "normal/acceptable"? For illustration, in the dropped tuning configuration, measuring 2.5 cm parallel to and below the bridge, I have 1.5mm droop on each end of a 40cm straight edge across the lower bout. When I increase to standard tuning, the increased bulge results in a 2.0mm gap on either side of the bout. Am I nitpicking, or might that be too much stress for a 33 year old Washburn??

That's likely a ply top, and I find these will bulge a lot.  Not much (practical) that you can do to remedy it.  Definitely tune down, as mentioned above, 12-strings are so much more fun in lower tuning (you can go heavier with the strings i.e.11-52-ish.

If you want a really cool 12 with the classic jangle sound, scour the web for a 60s-70s Harmany/Stella 12.  All solid wold, truss rod and short scale, made in USA.  With a tail piece, no worry re the bulge.  These can be had cheaply (1-300 needing neck resets etc.) and they're easy to work on.  Tons of them out there.  Great guitar for building your repair chops!

Tom

Thanks for the tip. I guess I'll learn to live with the lower tuning. I also might think about installing a JDL Bridge Doctor just for peace of mind. Seems to be a lot of support for that elsewhere here in the forum. Appreciate all your responses!

Rgds, Ryan

If a straightedge across the top behind the bridge only shows a 2mm gap at tension, you have no problem.

A ply top will bulge more than a similar thickness solid top because ~60% of the grain is oriented the wrong way to resist the torque on the top from string tension.

Besides looking at that gap, look in the reflections on the top for "wrinkles", areas that dip or bulge, that might indicate an area where a brace is loose.

Bridge Doctor is a last resort.

Ah ha, now I'm starting to feel more comfortable. The bracing of the top is all intact, as far as I can see and feel. The reflections clearly show a quad shaped "ramp" originating at the bridge and tapering out towards the bottom of the bout. It is no doubt a torsion induced deformation and I can live with it based on your advice that the 2mm gap is "no Problem". BTW- there is no perceptible "sinking" of the surface forward of the bridge towards the sound hole, which I suppose is a further indication of the structural integrity. Your comment on the ply top makes good sense in this case. A last question...would the installation of the Bridge Doctor (brass pin version) be good insurance, as well as a "last resort", or could it in some way be detrimental?  Thanks again for your advice!

Keeping in mind that I don't have the guitar here to look at, I'd say it's just not necessary. The brass pin version won't do any harm, but it does change the tone of the guitar to some extent.

Advice taken... I'll quit while I'm ahead.

Many thanks!

I first got interested in the 12 string guitar in the early 1960's. I was listening to Leadbelly (Huddie Ledbetter), Pete Seeger and others who played very low tunings with very heavy strings. To me, the 12 string needs to have the low tuning, but that's just my opinion. At to pulling the top up, yes, tuning to pitch can do that to a lesser or greater degree on a 12 string depending on the model of guitar.

I have two 12 strings: a 1965 Martin D-12-35, one of the first ever built and also a 1963 Gibson B-25-12 N. The Gibson has a tailpiece so there's no pulling of the top. The Martin has very little bulge even after more than 50 years. Both instruments are tuned two half steps low to D with Martin light gauge 12 string guitar sets.

Good luck on your guitar playing!

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