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  #16  
Old 10-05-2018, 09:14 PM
John Arnold John Arnold is offline
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Quote:
if an instrument has been built with fresh Titebond
That is not a given these days, considering the new interest in hot hide glue in the segment of the boutique market geared toward vintage recreations.

Alan is relating experience that mirrors mine....and I have been a full-time repairman for 34 years. One thing that I have learned is that Martin had good reasons for doing things a certain way.......including inletting the X-braces and the upper transverse brace into the kerfing.
One of my latest examples is a 1934 00-21, which had a gap where the upper end of the X-brace entered the kerfing. Not only was the brace loose on the end, but there was a top crack about 1" in from the edge....right where the peeling of the brace ended.
I have repaired literally hundreds of Gibsons that had braces that were loose on the ends. The 00-21 cited above is a rare case for a Martin.....one where the execution was flawed.
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  #17  
Old 10-05-2018, 10:17 PM
mirwa mirwa is offline
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Originally Posted by Alan Carruth View Post
It's peeling in the sense that the glue line comes loose starting at one end and progressing along the length of the brace.
Yep, see it all the time, any glue that has the ability to creep is prone to this phenomenon, it slowly peels the glue bond along its length

Hard photo to see, but this is for others, typical Gibson

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  #18  
Old 10-06-2018, 07:34 AM
murrmac123 murrmac123 is offline
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Ah well, there's no arguing with all that weight of evidence, and Steve's picture, so obviously it does happen.

I would assume that it's down to the 180 lbs tension, and the constant vibration of the top which somehow degrades the composition of the glue in the long term, rendering it susceptible to any impact causing the joint to fail along it's length.

Still can't help feeling that it shouldn't happen, since a well glued joint is, or should be, stronger than the wood itself, but there you go ...
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  #19  
Old 10-06-2018, 08:44 AM
ruby50 ruby50 is offline
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No one yet has mentioned that gluing braces onto plates violates a cardinal rule of woodworking. Don't try to glue cross grained pieces together, but design a joint that allows for movement. Think breadboard ends on a table where you might glue the center of the joint, but rely on pins in oval holes at the outside edges for movement.

A quarter sawn spruce top at 16" wide with a typical change in RH we see in a house might result in up to 1/8" or so of added width in the higher humidity season, where the brace glued across the grain will be essentially no longer. The stresses on the glue joint can be significant.
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  #20  
Old 10-06-2018, 08:52 AM
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I know nothing, but was wondering after reading this thread, could the braces be let into the liners as is the norm, with a light pressure fit both width and thickness, but left unglued to the liners, would that solve both issues? It may allow more movement and hence more vibration in the "freer" top but provide the support for the braces so the glue joint would not peel.

If anyone watches treehouse master, it would be analogous to how they brace to one tree firmly, but the other tree has a bracket that allows the headers to slide back and forth to allow the whole structure to move without cracking of any of it?
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  #21  
Old 10-06-2018, 09:34 AM
redir redir is offline
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Maybe tucking the ends is why a Martin has a Martin sound? IDK.


It seems to me to have an impact on tone. Classical guitar makers will thin the edges of the plate in the lower bout and of course all the fan braces are feathered to zero. The idea I think is to loosen the edges so the top has more of a pump.
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  #22  
Old 10-06-2018, 10:03 AM
printer2 printer2 is offline
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Quote:
Originally Posted by TomB'sox View Post
I know nothing, but was wondering after reading this thread, could the braces be let into the liners as is the norm, with a light pressure fit both width and thickness, but left unglued to the liners, would that solve both issues? It may allow more movement and hence more vibration in the "freer" top but provide the support for the braces so the glue joint would not peel.

If anyone watches treehouse master, it would be analogous to how they brace to one tree firmly, but the other tree has a bracket that allows the headers to slide back and forth to allow the whole structure to move without cracking of any of it?
In the Spanish Foot type of build the sides are inserted into slots in the neck. these can be glued in or just wedged without glue. So it is possible but it is the thickness of the brace at the end glue to the top that gives the stiffness to the edge of the top rather than the end of the brace glued into the lining.
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  #23  
Old 10-06-2018, 11:16 AM
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Quote:
Originally Posted by printer2 View Post
In the Spanish Foot type of build the sides are inserted into slots in the neck. these can be glued in or just wedged without glue. So it is possible but it is the thickness of the brace at the end glue to the top that gives the stiffness to the edge of the top rather than the end of the brace glued into the lining.
Got it, but as the OP was thinking not having that connection of the braces to the sides ie. ending the braces before the lining would free the top. It would not really though at all as the top is glued to the linings all around anyway so even if the braces were not let in and glued the top would not be any freer...right, got it.
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  #24  
Old 10-06-2018, 03:57 PM
Alan Carruth Alan Carruth is offline
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Most of the outright failures I've seen were on old Gibsons, assembled with hide glue. Old hide glue gets pretty brittle, and the brace ends were not supported properly on those, as I said. Regular Titebond has better peel resistance: I'm not so sure about T2. We don't know how that stuff will be in a hundred years.
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  #25  
Old 10-07-2018, 04:04 PM
phavriluk phavriluk is offline
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I think Taylor makes a point of mentioning that they cut a channel on the back of the soundboard inside the contact with the kerfing so as to allow the soundboard to vibrate more easily. I haven't heard complaints about Taylors' soundboard bracing detaching at the untucked ends.
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  #26  
Old 10-07-2018, 04:43 PM
Shuksan Shuksan is offline
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Quote:
Originally Posted by phavriluk View Post
I think Taylor makes a point of mentioning that they cut a channel on the back of the soundboard inside the contact with the kerfing so as to allow the soundboard to vibrate more easily. I haven't heard complaints about Taylors' soundboard bracing detaching at the untucked ends.
In the photo below of a Taylor with a relief route around the inside edge of the soundboard, you can see that the relief cut stops when it reaches an x-brace end and the x-brace end is tucked under the kerfed lining.

[IMG][/IMG]
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  #27  
Old 10-07-2018, 05:28 PM
phavriluk phavriluk is offline
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Thanks very much. Never been exposed to an example.
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  #28  
Old 10-07-2018, 09:52 PM
John Arnold John Arnold is offline
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I have seen the Taylors fail at the routed groove. It is definitely more susceptible to impact.
I don't believe vibration weakens the glue. Hot hide glue is naturally brittle as soon as it cures.
Below the bridge, the force from the string tension is pulling up on the top. That will not cause the braces to pull loose on the ends.
As has been mentioned, the primary reason for inletting braces below the bridge is to account for incidental pressure or impact on the top from the outside. Above the bridge, the force is downward......hence the necessity of inletting the braces in that area.
Are the inletted X-braces responsible for the 'Martin sound'? It probably is a small contibutor.
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  #29  
Old 10-08-2018, 12:50 PM
Alan Carruth Alan Carruth is offline
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HHG has very low shock resistance. That is actually a desirable feature in some uses: violin repair people take advantage of it all the time. Cheap violins assembled with white glue or Titebond are considered unrepairable: it takes too much time and effort to get them apart and clean off the old glue.

HHG actually creeps less than Titebond, which is, itself, much better in that respect than the white glues that many low-end manufacturers use. White glue, such as 'Elmer's', is, IMO, the equivalent of bubble gum: it doesn't really hold anything but you can't get it loose either.

When talking of the strength of a glue joint it's well to keep in mind that much of the volume of any piece of wood is actually air. Glue fills in that air space on the surface, and is certainly stronger than the air. There's debate on whether the strength of a glue bond is more chemical or mechanical. Certainly both have a part.

Having braces that run across the plate certainly does cause problems. It's common on old guitars for the brace ends to make bumps in the sides where they push against them. The top and back get narrower, but the braces don't get much shorter. A helpful refinement for the builder is to cut the brace ends off just shy of the sides, leaving a mm or so of gap. The brace ends are supported by the inlets, but (maybe) the sides won't bulge out later. We'll find out if this works in a hundred years or so....

All of this is somewhat beside the point of the original post, which speculated on the effect on tone, iirc. As I said before, it certainly ought to have some such effect, but that's moot: a good maker inlets the braces for necessary structural reasons and lives with any tonal loss.

Last edited by Alan Carruth; 10-08-2018 at 12:59 PM.
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  #30  
Old 10-08-2018, 04:56 PM
murrmac123 murrmac123 is offline
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Quote:
Originally Posted by Alan Carruth View Post
a good maker inlets the braces for necessary structural reasons and lives with any tonal loss.
Great post Alan.

Just to clarify, are you saying that IYO it is mandatory for the lower brace ends to be inlet into the kerfed linings (sic) in order to ensure stability ?

Obviously the upper brace ends have to be inlet... no dispute there ... it is not immediately, intuitively, apparent that the same necessarily applies to the lower brace ends.

I am tempted to take a trip down to the Acoustic Music Centre in Brighton, where Trevor has a vast array of high end boutique guitars, and see just how many builders do in fact inlet the lower brace ends rather than leaving them feathered to zero.
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