Building (M20) Bridges

jedzep

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Hi y'all.

The front wall of the saddle slot on my already once repaired/glued bridge is acting up, leaning again from string break angle pressure forward. A hard to find part, if I must, even with Hans' help, so I ask here if anyone has a recommendation for someone they might have used who can turn a BRW blank into a facsimile of an early Guild flattop bridge. Crazier yet, would you consider buying the Guild USA M20 version, fill in the pin holes, then re-drill to 2 1/8" spacing, as an option. Suggestions are welcome.

Thanks...Dave

 
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adorshki

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A hard to find part, if I must, even with Hans' help, so I ask here if anyone has a recommendation for someone they might have used who can turn a BRW blank into a facsimile of an early Guild flattop bridge.
There've been a number of comments over the years that carving a new bridge from a blank isn't a particularly difficult proposition, especially for a skilled luthier, so I'd at least vote for focusing on that angle, and that way, it'd still Braz, to boot.
 

Nuuska

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Topic related question.

Does any guitar builder cut the slot for the saddle in an angle that would be in the direction of the string pressure against bridge?

 
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kostask

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That would require a complete rethink of the guitar top. The tension of the strings is no longer acting directly downwards, so the back and forth motion of the saddle and its effect on the top is no longer in play. The string forces would take some math to resolve, but as a first cut look at it, the forces are now tangential (pushing forward as well as down, but not down as forcefully as a vertical bridge) to the top. This would result in lower volume, at least, with possible effects on the tone. Some of that may be recovered by re-thinking the bracing, or not.
 

evenkeel

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Before I went down the road of replacing the bridge I'd look at cutting a new saddle from a wider bone blank. You want the saddle to fit tight into the bridge and this appears to be a bit loose. I'd also make sure the bottom of the slot in the bridge is perfectly flat and the bottom of the new saddle is also perfectly flat. Finally, the break angle looks very high. If there is room to lower the action w/o buzzing that would also help.

If all that is a non-starter then contact Tom Jacbos, a'ka Fixit here on the forum and see if he can make a bridge for you. He did a neck re-set on my F-212. The bridge had been shaved down and we discussed making a new bridge. In the end we opted to add a rosewood shim under the existing bridge. We could have gone the new bridge route so I'm pretty sure he could make one for you if that's the best option.

Hope this helps
 

jedzep

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Big thanks for the reference and smart advice. There are other aspects to this fix, as you observed, including the saddle height and worn string slots off the pin holes, causing quite a forward push on the saddle off the severe break angle. When my talented luthier repaired the bridge a few months back he did adjust the saddle thickness and level the contact surfaces, but I will ask him to take some off the height if he can. I don't think it helped that one of my kids tuned it to standard pitch over T'giving, up a whole step from D-D, with heavier 13's on. By the time I noticed the damage was done.

 

evenkeel

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The side picture also shows you have some room to route the slot in the bridge a bit deeper. That would help support the saddle.
 

adorshki

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That would require a complete rethink of the guitar top. The tension of the strings is no longer acting directly downwards, so the back and forth motion of the saddle and its effect on the top is no longer in play.
Don't think the saddle actually "moves" in any direction even if it's loose in its slot:
It's held in place and even "pulled forward" towards the nut when under string pressure.
Also the only real movement taking place is the top itself when vibrating from the energy introduced through the saddle into the bridge, whose mass then helps get the top "moving".
Any motion of bridge and saddle is result of top motion, unless one wants to describe the vibrations and the transmission process itself as "motion".


The string forces would take some math to resolve, but as a first cut look at it, the forces are now tangential (pushing forward as well as down, but not down as forcefully as a vertical bridge) to the top. This would result in lower volume, at least, with possible effects on the tone. Some of that may be recovered by re-thinking the bracing, or not.
The real problem with that geometry is that the angled saddle inherently creates an obtuse break angle, and that's going to have the same effect on volume as a low saddle.
The reason low saddles cut down on volume is because they also create "wider" (more obtuse) break angles.
The sharper the break angle, the more string energy is transmitted to the top, thus the vertical saddle.
And why ramping of bridgepin holes is a common cure for low break angles on otherwise well set-up instruments.

The side picture also shows you have some room to route the slot in the bridge a bit deeper. That would help support the saddle.
I wouldn't make that judgement too lightly, for one thing it may invite cracking along the slot, and in fact the 'front wall" of the slot is already giving way under the lever-like effect of the string tension pulling the saddle forward, so think deepening the slot will only amplify that leverage.
Lowering saddle is a goo stop-gap, I think, but this may be one of those scenarios where the glue bond simply won't stand up to the torque of the saddle torque in its slot.
Your suggestion of Tom Jacobs for getting a new saddle made is very good in my opinion, though.
 
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evenkeel

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The saddle should not need to be glued. I have guitars with both drop in and thru saddles. None of them are glued. The downward force of the strings, plus a good snug fit is all that is needed.
 

jedzep

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Hah! You read my mind. Never glued, never will.

A complex discussion has blossomed, nonetheless. I couldn't pass high school physics, but I love hearing guitar freaks talk it. A good group!
 
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adorshki

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The saddle should not need to be glued. I have guitars with both drop in and thru saddles. None of them are glued. The downward force of the strings, plus a good snug fit is all that is needed.
Think you were answering this part of my post?
Lowering saddle is a good stop-gap, I think, but this may be one of those scenarios where the glue bond simply won't stand up to the torque of the saddle in its slot.
I see it was poorly worded, didn't mean to imply the saddle was glued (you're absolutely right, should only need to be held in place by string pressure and snug fit);
I meant the glue bond of the repair of the bridge.
(And used "torque" twice too, when re-writing and editing too quickly, LOL!)
I thought the problem was that the front side of the slot had a crack in it caused by the stress of saddle pushing forward, due to Jedzep's first sentence in the OP:
"The front wall of the saddle slot on my already once repaired/glued bridge is acting up, leaning again from string break angle pressure forward"
And was trying to address the fact that even though glue bonds are supposed to be even stronger than the original wood, I thought the torque of the saddle against the "front wall" might be enough overcome that usual rule, in this case.
 
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jedzep

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And that's the way it is, Al. The string slot worn toward the saddle ain't helping either.

You bring the car in for an oil change and you come away with a valve job. She's leaning again.

Over the holidays I think my boy tuned it to standard pitch, as I might have mentioned. That didn't help with the 13s on.


 
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adorshki

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And that's the way it is, Al. The string slot worn toward the saddle ain't helping either.

You bring the car in for an oil change and you come away with a valve job. She's leaning again.

Over the holidays I think my boy tuned it to standard pitch, as I might have mentioned. That didn't help with the 13s on.
Right, saw that, suspect that was the stress that broke the bridge's back, so to speak.
Certainly couldn't-a helped, and at least not catastrophic.
:friendly_wink:
 

gjmalcyon

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If the current bridge height is OK, you could enlarge the existing saddle slot, glue in a piece of rosewood and after it dries, cut a new saddle slot. My F-47 (purchased from mikemo6string) had that done. The intonation was off just enough that Mike had his luthier fill the existing saddle slot and cut a new one. It is almost invisible - if I did not point it out you would not see it.
 

adorshki

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If the current bridge height is OK, you could enlarge the existing saddle slot, glue in a piece of rosewood and after it dries, cut a new saddle slot. My F-47 (purchased from mikemo6string) had that done. The intonation was off just enough that Mike had his luthier fill the existing saddle slot and cut a new one. It is almost invisible - if I did not point it out you would not see it.
Ooooh, I LIKE that!
:smile:
 

evenkeel

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If the current bridge height is OK, you could enlarge the existing saddle slot, glue in a piece of rosewood and after it dries, cut a new saddle slot. My F-47 (purchased from mikemo6string) had that done. The intonation was off just enough that Mike had his luthier fill the existing saddle slot and cut a new one. It is almost invisible - if I did not point it out you would not see it.
That's a very good observation/suggestion. I like that idea a lot.

Adorshki, I see that I did not interpret your comment re: gluing correctly. You're right a re-glued bridge may well not have enough strength or structure. That makes the above suggestion from GJmalcyon more valid. Plus. you could then deepen the slot so there is more saddle below the bridge slot which should help.
 

adorshki

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That's a very good observation/suggestion. I like that idea a lot.

Adorshki, I see that I did not interpret your comment re: gluing correctly. .
NO worries, there was also the possibility I'd misinterpreted jedzep's original explanation, myself.
:friendly_wink:
 
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