Replacing a harmonic bar--advice sought (Full Version)

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constructordeguitarras -> Replacing a harmonic bar--advice sought (Sep. 12 2017 2:24:43)

I have a good friend who made a guitar years ago. I recently showed him how to french polish it properly and we discovered that the lower harmonic bar had warped and made the top concave, something I've never seen before. The bar is much smaller in cross section than usual. In addition, my friend did that thing where the bar is hollowed out near the ends to allow fan braces to extend into the upper bout, which weakened it.

While we were working on the finish, I vacuumed out the inside and we heard a loud crack, which was apparently one end of the harmonic bar--which was held on by a little short grain--popping off.

I proposed gluing in an additional lower harmonic bar adjacent to the first to push it back into the proper shape. We did that but within a day the ends of both bars popped off. That warped bar is just too strongly holding its wrong shape.

So now I propose to route the back binding off, remove the back, and remove and replace the lower harmonic bar(s). Does anyone have experience doing this sort of thing? Any advice?



jshelton5040 -> RE: Replacing a harmonic bar--advice sought (Sep. 12 2017 13:29:21)

quote:

ORIGINAL: constructordeguitarras
So now I propose to route the back binding off, remove the back, and remove and replace the lower harmonic bar(s). Does anyone have experience doing this sort of thing? Any advice?

Rout just deep enough to expose the edge of the back, that way you don't have to replace any side purfling. I've done it a few times, getting the back off in one piece without damage is the tricky part. What kind of glue did your friend use?



constructordeguitarras -> RE: Replacing a harmonic bar--advice sought (Sep. 14 2017 0:31:28)

Thanks, John, good advice. He used white glue, which I guess won't be quite as responsive to a hot knife as hide glue would.



jshelton5040 -> RE: Replacing a harmonic bar--advice sought (Sep. 14 2017 2:20:49)

quote:

ORIGINAL: constructordeguitarras

Thanks, John, good advice. He used white glue, which I guess won't be quite as responsive to a hot knife as hide glue would.

Even white glue softens with a little heat. A heat gun applied judiciously will help separate the joints. It may damage the finish but that's an easy fix if it's FP. It's definitely not a project I enjoy. Good luck!



Stephen Eden -> RE: Replacing a harmonic bar--advice sought (Sep. 14 2017 7:45:25)

would you not want to go down as far or close to the side perfling? That would make putting the new binding on a little easier perhaps? Less would colour mismatch also you might expose the back bars enough to prise them loose too, avoiding another battle.



estebanana -> RE: Replacing a harmonic bar--advice sought (Sep. 14 2017 8:09:21)

If the lower lateral brace is loose you can lay waste to it, leaving only the upper lateral to deal with. So I would cut off the fingerboard at fret 11 and remove the fingerboard extension over the body and take the top off. Then you don't have to mess with the three back braces.

While you're at it, just cut the upper lateral brace out and replace upper and lower. Use a fresh X-acto razor saw to cut the top from the rim.

Or, rout down only enough to reveal the seam between back and rim/braces and use an iron to heat the glue enough to gee it to release and pull the back off the braces like a skin.

If he used yellow of white glue it's possible with lots of care to remove the glue off the braces with palette knife insertions of paper towel dipped in oxalic acid water solution. Slow work but it can be done with precision. Razor saw the back off the rim and lower block then one brace at a time get between top and brace with a knife and water.

If it were hide glue the back would could peel off the braces like skin. It's kind of fun. The ribs don't distort. Added bonus.



constructordeguitarras -> RE: Replacing a harmonic bar--advice sought (Sep. 14 2017 14:01:59)

quote:

would you not want to go down as far or close to the side perfling?


Thanks, Stephen. I've been thinking about this but haven't started yet and may not for a week or so. There is no side purfling. And it's not the prettiest guitar, and since I won't be able to route into the heel, I'm thinking that minimal depth as John described might be easiest because I will have to carefully chisel out the "bee sting" to the same depth. The back lining is that kerfed stuff and I am hoping that the ends of the back bars are not attached to anything. I can always go deeper if necessary, so I am thinking of starting out shallow and hoping to lift out the back with the bars attached.



constructordeguitarras -> RE: Replacing a harmonic bar--advice sought (Sep. 14 2017 14:05:54)

quote:

Then you don't have to mess with the three back braces.


Thanks, Stephen. See what I replied to Stephen above.

I appreciate your suggestions. Will consider.



Tom Blackshear -> RE: Replacing a harmonic bar--advice sought (Sep. 14 2017 17:33:22)

What if the top is not too distorted and you just put some new glue in and leave it at that. I've noticed the 2004 Reyes was inverted to some extent, going across the lower harmonic bar but didn't hurt its operation.

Or why not replace the top? Too much expense?



constructordeguitarras -> RE: Replacing a harmonic bar--advice sought (Sep. 14 2017 18:50:16)

Thanks for your comments, Tom.

My friend says that the top seems to collapse under string tension where it is concave. We discussed the risks of taking off the back and he said it's useless to him as it is, so worth the risks.

Since both lower bars' ends popped off after I glued in the additional one, we think it unlikely that they would hold if reglued. Removing a top seems more daunting to me than removing a back, and we'd like to keep as much of the original guitar as possible.



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