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I have a guitar with a sound that I like very much. I'd like to replicate that sound as closely as possible on another guitar that I am building. These are flamenco guitars with the same plantillas, bracing patterns/materials and virtually everything else except for back and side material. My thought is that I could do deflection testing on the top of the completed guitar and then adjust the top of the uncompleted guitar to comply with it by thinning the top and braces.

Here's the issue as I see it - the body of the in-process guitar is closed but doesn't have the bridge attached. I think I should glue on the bridge for the fine tuning of the top, but then remove the bridge for finishing. I'd like to get others' inputs as to how to get the bridge on and off without damaging the top. Your comments and suggestions will be most appreciated.

Thanks,
Max

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Max Bishop
Brighton, Michigan

BTW - I have built a deflection testing rig based on the one David Hurd (Left-Brain Lutherie) shows on his website.

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Max Bishop
Brighton, Michigan

Sounds like a perfect candidate for HHG

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Even with HHG it is easy to pull up wood fibres when removing the bridge. Pay close attention to grain direction. If you start to use heat and water that can also leach out dyes from woods like Rosewood, badly staining the soundboard. I'd be tempted to do a couple of thin coats of Shellac and glue the bridge on top of that. It can be scraped later.

Stew Mac makes little hollow bridge bolts that you can bolt the bridge down and still thread strings through. It will not replicate being glued down but you can get the bridge clamped down tight. Or if you are not going to try and string it up just use bolts with nuts and washers.

Bob

Those bolts would be for a pinned bridge tho right?

I would say HHG as well. I'm very curious to know how this works out for you so please report back when done.

OOPS... I guess I read right over that part...

In the words of the late Gilda Radner... "Never Mind"

Cheers,
Bob

Given that the guitar is already closed and you are working on the inside to shave the braces anyway. I would wait until after the finishing with the bridge on permanently before I did the fine tuning with the deflection jig.

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http://www.Harvestmoonguitars.com

Might be a dumb idea, but why couldn't you fashion a temporarly tailpiece that would screw into the strap button spot to
hold the strings over the bridge? Seems like a person could fashion one of those rather simply with 2 dowells and a couple
pieces of scrap strategically placed. Ignore me if that's a horrible idea.

Max,

I'd go with Colins suggestion.




Eric,

Strings attached to a tail piece put tension on the top in a different manner than when they are attached to a bridge. Because of these different loads this would not help in voicing the new top to the other guitar.



I didn't want to do that because it wouldn't help you understand the dynamics of the system. Now you have one more piece of info to add to your building arsenal.

Steve

Steven Wheeler wrote:
"Strings attached to a tail piece put tension on the top in a different manner than when they are attached to a bridge. Because of these different loads this would not help in voicing the new top to the other guitar."

The loading is different, but that does not affect the way the top works in itself all that much, according to the measurements I've made. Tying the strings to the bridge does produce a torque load that you don't get on a tailpiece, and enables the 'tension change' and 'longitudinal' signals of the string to drive the top, rather than only the 'transverse' signal that an archtop gets. This doesn't make much difference in the power output of the guitar, but it does show up in the timbre, as the 'tension' signal is octave-doubled with respect to the 'transverse', and the 'longitudinal' wave is at a much higher frequency than the fundamental of the string. Again, all of this is based on extensive experiments; it's not opinion.

Back when I started 'free' plate tuning I tried all sorts of ways to attach a bridge temporarily that would be as secure as gluing it, and would allow me to take it off without risk. I could't find any. I know people talk about popping off a hide-glued bridge with no problems, but I guess I just glue them on too well. Any double-stick tape that is reasonably secure will pull the grain, and even then it's not as secure as glue.

I have not tried Joe Curtin's trick for experiments as yet. He sizes the surfaces with hide glue, and allows it to dry. Then he uses CA to glue the parts together. The CA sticks to hide glue well, and the hide glue allows for getting it apart easily. Maybe it's better than what I've tried since it doesn't have to be clamped. I also doubt that you'd need to use CA all over the surface: just the edges should do. I'd want to practice first. When he gets things working the way he wants, Joe takes them apart, cleans off all the glue with warm water, and glues them up permanently with hide glue.

Thanks to all for your suggestions. I spoke to a luthier friend of mine about this question and he suggested using fish glue. He felt that that removing the bridge would be easier because it could be done by carefully loosening it with water rather than heat, as is the case with HHG. I guess I'm a bit scared of using HHG because I have no experience with it.

Anyone wish to share thoughts and/or insights on such an approach?

Thanks,
Max

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Max Bishop
Brighton, Michigan

I would just proceed to finishing and then glue the bridge and do any testing and bracing shaving then.
When I put on a bridge, I do it with the intention of it staying put.

really? how much water before it gets in deep into the joint? I think even with the fish glue you need heat, and there is a good chance you will damage your top as it sounds like this is the first time you are removing a bridge.

When I removed my first bridge I was very careful with the heat and the putty knife and I was able to cleanly lift the bridge, lo and behold I did not watch what was happening with the back side of the putty knife.

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http://www.Harvestmoonguitars.com

John Parchem wrote:

So John, what did happen with back side of the putty knife?

Thanks,
Max

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Max Bishop
Brighton, Michigan

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http://www.Harvestmoonguitars.com

I don't know, but I wanted to do that too: Cedar top, long scale, well fitted ebony rectangle bridge with a small bead of hhg on the trailing edge. 2 years later with heavy use, that sucker is still on there so good, I doubt it would ever come off on its own. The next time I do it, I will use a SUPER tiny bead.

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Pat

Pat,

Was that on a steel-string guitar?

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Max Bishop
Brighton, Michigan

I've found fish glue harder to remove than regular HHG. With hide glue dry is usually the best way to go: water softens the wood and tends to make more problems than it solves. You might try letting a batch of hide glue get really old and dark and thick, and then thinning it out a lot. That usually weakens it.

Thanks to everyone for their input. I don't know which route I'm going to take yet. I will post results once I decide.

Max

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Max Bishop
Brighton, Michigan

FWIW - I would vote for this method if you do not think you will need to thin the sound board.

But as the Padma say's, I'm a wannabe loofier

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EddieLee

Why not just finished the guitar with bridge on?
It will solve the problem isn't it?
I know lots of classical builders do it this way too.

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Sen CL Goh
http://senguitar.blogspot.com

Yes!

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Pat

I think I am going to wait until the guitar is finished and the bridge is on, then fine tune via shaving fan braces as necessary.

Thanks again,
Max

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Max Bishop
Brighton, Michigan