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Yesterday I was flipping through one of the many guitar building books I own and came across the section on bridge plates. The author said that the bridge plate should not be installed tight against the surrounding braces. He said there should be a small gap (like 1 mm). Anyway I have always installed my bridge plates tight against the surrounding braces. I suppose the thinking behind leaving the gap would be so that the wood has room to move.

What do the rest of you guys do? Install the bridge plate so it fits snug against the braces or leave a gap?

Josh Josh H38721.3763425926

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Josh House

Canadian Luthier Supply
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Snug, but not tucked.

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Lance@LuthiersForum.com

which book did you read this in?

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Lance@LuthiersForum.com

Snug but not tucked for me also Josh

I alway get the pressed right up against the x-brace. No gaps...I'm curious where you read this as well.

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John Mayes
http://www.mayesluthier.com

The book was Build Your Own Acoustic Guitar by Jonathan Kinkead. I went back and read it again to be sure. He doesn't explain why he says you should leave the gap, he just says you should.

I am doing the same thing all you guys are, which is the way I thought most builder did the bridge plate. I had never come across this before so I thought I would get some feedback. I will continue to fit the plate snug against the X brace.

Josh

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Josh House

Canadian Luthier Supply
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House Guitars - Custom Built Acoustic Instruments.
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Snug not tucked also... I have the Kinkead book also, not a bad book but this particular thing didn't make sense to me...

-Mark

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   Snug, tucked and every little nook and cranny filled with West System epoxy...

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Snug, well-fitted, not tucked.

Alain

What is your thinking behind the epoxy. Are you gluing your braces on with epoxy as well?

Josh

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Josh House

Canadian Luthier Supply
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House Guitars - Custom Built Acoustic Instruments.
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Josh,

You can e-mail Jonny Kinkead if you like and ask him. He is a great guy and very willing to answer questions presented in his book. I sent a couple of sample tops to him, the next thing I know I got an autographed copy of his book in the mail! he is quick to respond to e-mail as well. He also offered to assist whenever required. If you prefer, I can pose the question to him but I am absolutley sure that he will get right back to you with his reasons.

Shane

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Canada

Wow. Its refreshing to find an industry where people are actually nice to each other. Reading this forum is going to take years off my learning curb...

What does it mean to "tuck"?

Some folks notch the bottoms of their braces to allow the bridge patch (and tone bars, etc.) to tuck under the x-brace slightly.

The repair people usually prefer that you DON'T do that. If the bridge patch needs to come off in a future repair that makes their job a lot harder.

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Brock Poling
Columbus, Ohio
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   Josh, I glued everything on the top with LMI's white glue (which I love for soft wood to soft wood bonds - and don't like with hard to soft...). I just put in the epoxy (thickened with silica) in every little nook and crany that I could find on the top (brace pockets etc..) in case it decided to start buzing or developing funny ideas! I had a little left over so I just spread a thin coat on the bridge plate for added rigidity. Overkill? Maybe, maybe not.

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I'd like to be able to prove, just for once, that money wouldn't make me happy...

I think John Kinkeads theory with leaving a gap round the bridge plate is that it allows the plate to drive the top without having to drive the X as well.

Guess it depends on how you view moment of the top. I have had the fortune to have a couple of Johns guitars in my hands and he makes some very nice guitars.

It often seems to me that a good idea is to either tuck things in, as in brace inlets, or avoid contact. Any time things just touch it seems like there's a chance for buzzing. Bridge plates are one place I'm inconsistent with that. I like to get things tight, but not tucked, for the reasons given.

Driving the top but not the braces: that's a new one....

HI Al

Obiously if the top moves so do the braces hopefully

What I mean is drive with no direct conection to the X Brace, the theory being that it takes less energy to get things moving and the X has no Dampening effect, as the energy disperses.

I can provide no direct scientific data on this so it may be absolute nonsense ?

Snug as a bug BUT not under the rug ;)

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tim...
http://www.mcknightguitars.com

Tight up agaist the X but not tucked.

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Jim Watts
http://jameswattsguitars.com

This has been informative.

When I first read about the gap it made me wonder if lots of other people did that and I was missing the boat. I didn't recall seeing that on other builder’s guitars. It seems to me that the most common way is tight but not tucked. I had never thought of tucking the bridge plate (I tuck all the rest of my braces). It would sure be a nightmare if for some strange reason you ever wanted to remove it in the future. I may email Jonathan and ask him about it if I get the chance.

Josh

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Josh House

Canadian Luthier Supply
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House Guitars - Custom Built Acoustic Instruments.
http://www.houseguitars.com

[QUOTE=Alain Desforges]    Josh, I glued everything on the top with LMI's white glue (which I love for soft wood to soft wood bonds - and don't like with hard to soft...). I just put in the epoxy (thickened with silica) in every little nook and crany that I could find on the top (brace pockets etc..) in case it decided to start buzing or developing funny ideas! I had a little left over so I just spread a thin coat on the bridge plate for added rigidity. Overkill? Maybe, maybe not.[/QUOTE]

I've only built one kit guitar but did just this very thing thinking that a rigid plate would transfer energy better. But I definitely snugged the plate up to the X, as a matter of fact I forward shifted the braces so the kit formed plate would have sat about 1/4" behind the X. Just didn't seem right so built another that was snugged up against the X.

Have NO idea what effect this might have had on tone just seemed like an OK idea. It also seems like great idea to leave a gap - seems like so many variations work.

Larry

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Russell & Al,

I always thought that the X braces are part of the process of getting the strings energy via the bridge/saddle into the top as well as giving structural stability, and in part that's why I use a very tight X brace angle (78 degrees) so that the X brace legs are close to the outer strings.

As with many things I could be - and probably am - totally off beam (or off braces)

I have my bridgeplates touching the braces but withh all of the edges of the plate feathered/beveled down.Dave White38722.3177546296

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Dave White
De Faoite Stringed Instruments
". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010

You really have to think of the whole top/bridge/braces/bridge plate as a system, especially at low frequencies. It's a lumpy system, and where and how big the lumps are is part of what 'makes' the sound, but it's all one thing.

In terms of 'tranferring energy', one of the key concepts is that of 'impedance'. It's basically a measure of how hard it is to move something at a particular frequency: technically the ratio of Force/Velocity at a given point and a given frequency. Making something stiffer or heavier raises it's impedance overall, but mass and stiffness change the frequency relationships in opposite ways.

If you have two vibrating objects with the same impedance that are coupled together then all of the energy can flow from one to the other. A 'trivial' example of this is the string: each section of string is the same as every other, so that a wave that starts down the string just keeps going. If you put a 'lump' on the string that changes the impedance at that point, and some of the energy is reflected. It doesn't take much: try making a little 'flag' of masking tape, about 1/4" long and 1/8" wide and putting it on the string down near the bridge. You should easily be able to hear the difference in tone.

One of the main 'jobs' of the bridge is to provide enough of an impedance mismatch at all frequencies so that the string 'knows' how long it is. The bigger the mismatch the 'better', in the sense that you will be less likely to have 'wolf' notes owing to top vibrations feeding back into the strings, and such like. This is one reason light strings sound different from mediums: the lighter strings have lower impedance, so there's generally more of a mismatch.

But the impedance is frequency dependant. At a resonant frequency the impedance is always relatively low; that's one of the definitions of resonance. We all know that making the top stiffer raises the resonant frequencies, while adding mass without changing stiffness drops them. A bridge plate adds both mass and stiffness, and it's the overall balance of mass and stiffness that decides the outcome.

At low frequencies, when the top is vibraing as a unit, details of the way the plate and braces join aren't as important. As you go up in pitch the little things count for more. It's often the details of the high-frequency tone production that 'make' a good guitar, so those little things can have an acoustic effect.

The problem is the high-frequency workings of the guitar are so darned complicated that it's almost impossble to say categorically that something is 'good' or 'bad'. It all depends on how the thing works with _this_ set of wood and _that_ bracing scheme. Ultimately you have to figure out the features that work for you with your designs.

So, acoustically, I think that whether you leave a gap or tuck in is probably small potatos, compared to other stuff like 'scalloped, tapered or straight', or probably even the X angle. OTOH, you might find that it makes a difference to you. For me, considerations of repairablilty and buzzing supercede other stuff.