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I've just received a Martin Auditorium 000C-16GTE for repairs. It's the first instrument that I've seen with a MICARTA fret board and bridge. Many factory guitar makers now leave 1/8" of finish (to save on the production costs?) around the top plate's (bare wood) gluing area which gives the appearance of a lifting bridge. With less bonding area, the bridges often do begin to lift. Having little experience with this man-made substance (MICARTA), I am wondering what characteristics it has:

Does heating (for removal) warp or melt it?
What glues are compatible with this?
What are the working characteristics as a fret board or bridge?
(I have found that bridge pin holes are harder to ream)

Tags: MICARTA, PARTS

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I've got a cracked X-brace in a mandolin which will require hide glue along with long preparation and planning to accomplish in an almost inaccessible location. This natural glue offers the advantages of becoming thin enough to penetrate the crack as well as loosening with heat in other applications where removal may become necessary. While epoxies offer a much longer working time, they do remain gummy. Glue kills sound. The thinner the glue joint the stronger it is.

Regardless of the popularity of any current practices, we must do our own testing of materials to know what motivation was involved in the choices made.

Laminates provide toughness but fail to offer the needed stiffness (in top plates especially) or sound properties owing to the glue layering (a boat hull wants to be acoustically dead).

Grain fillers tend to hide the wood grain since they are not perfectly clear. More coats of lacquer means more work but brings out the natural beauty of the wood rather than dulling the appearance of the wood grain. Figure out what your priorities are and then proceed.

John, I'm sure you mean well here, but, opinion and compensation for poor practices or inappropriate choices of adhesives does not replace the manufacturing specifications and inherit qualities of various glues and their uses. 

The statement 'the thinner a glue is the stronger it is" is simply not valid across a range of different glue types - read up on the subject of intermolecular bonding versus mechanical bonding and while you are there check out any of the epoxy manufactures (excluding the corner store 5 minute epoxy makers which make kids epoxy) for the thickness requirements to sustain proper curing and hardness of epoxies.   "Gummy" epoxy is simply low quality,  poorly applied and/or badly cured epoxy.  Aircraft and Rockets (gluing is Rocket Science in this case) are put together with epoxy glues for a good reason (both wooden and composite). 

Similarly, the statement "Glue kills sound"  is meaningless and vague in the extreme - Sonic ray path plotting would show that different densities of  layers of glue can actually enhance and reinforce reflected rays/frequencies or refract primaries and secondary harmonics to add richness or complexity to the absorbed frequencies - it can also cancel and deaden response which is what you are saying, but the point is that a bland assertion is not helpful in understanding the complete mechanisms and couplings that occur.  

And to avoid a fight in the sandbox here,  my particular professional wall hanging relevant to this is a qualification in Advanced Acoustic Analysis from JAAC (RAF)  UK specializing in sonic ray path plotting and acoustic spectrum analysis and sampling.  I'm not saying don't argue but it's something I was passionate about.

The good folk at "Fine Working" ran exhaustive testing, under lab and controlled conditions, on glue application, strengths, qualities  and destruction testing for all our main types of glues - probably a good article to read to get an idea of what really goes on with glue.

Grain filler, and how and when to use it is a subject most full time luthiers have sussed - it's used when necessary or when a certain look is required.   Filling grain with lacquer provides about the same overall density as quality filler. We often use a dark stain filler to emphasize the beauty of open grained wood anyway which is kind of like "enhancing" rather than "hiding".   Also, shooting endless coats of lacquer to fill up the gaps is ecological vandalism these days, unless you are using water based lacquer.

Anyway, how glue works is not up to me or subject to my opinion - it's just science and physics and application -  but incomplete, exceptional or inaccurate fragments of information or opinion are the basis of folk-law and voodoo and don't do any favors to our knowledge base.   Anyway, I  do not intend to have the last word here so I'm all ears.

 

+1. "... incomplete, exceptional or inaccurate fragments of information or opinion are the basis of folk-law and voodoo and don't do any favors to our knowledge base."

Well stated. I've offered incomplete, exceptional or inaccurate fragments of information or opinion more than once, (and on this board, I might add) and welcome the opportunity to have the light of truth shone on my seemingly inexhaustible store of ignorance.

"Sonic Ray Path" is now the name of my new punk trio.

BTW, Martin is using Black Richlite for fingerboards and bridges. I'm not sure how much difference there is between this and "Micarta". From the Richlite website..."Richlite is made in Tacoma, Washington by Rainier Plywood -- a privately owned company that has been in business since 1943. Richlite solid surface sheet products were the result of research collaboration between Rainier and Boeing Aircraft. Boeing engineers were hoping to find a material for their template shop that had greater strength than Plywood. So the joint team of engineers introduced paper soaked in phenolic resin and heat pressed until stable. The result was Richlite, a non-porous and very strong material.

The color is solid all the way through the thickness of Richlite (thicknesses available from 1/4" up to 3"). There are ten colors to choose from, each having a warm, mat appearance -- a welcome alternative to the glare of the high gloss choices abundant today.

Major Certifications of Richlite include:

1. FSC™ (Forest Stewardship Council) which means that a chain of custody is maintained from managed forests.

2. Greenguard for Children & Schools, the top safety rating test for volatile organic compounds (VOCs)


3. And the popular food-safe certification, NSF 51, for commercial food prep surfaces...".

Guys, Yep sorry about that...I rewrote that post a couple of time to try and get the points across in a neutral way, in the end I just pressed the button.   Anyway, I have had my palm read a few times on this forum (and it is the only one I contribute to because of its quality and moderation) when I have been beyond dumb - it's a pleasure in this environment.   And, there is no easy way to say Sonic ray path -  its the science of determining what part of sound spectrums travel through changing acoustic densities and where they go from the "normal" when they encounter changing conditions.   Its useful knowledge from time to time if you have trouble sleeping.

The "thinner the stronger" actually was in reference to aliphatic resin typically used by luthiers. The epoxy I referred to is an industrial grade product: EA-40. Consistency in materials and densities best allow sound travel. About every 20 years scientific explanations of art and/or musical sound production resurface. I do not know that they have contributed to the consistency or improvement of either. In an 'Age of Information' we all too easily become infatuated gatherers and are overwhelmed with changing statistics and materials, usually influenced by profit or politics. When is enough enough? Perhaps the best advise is to simply choose your tools and materials and then concentrate on doing the work. I build to a higher standard with complete consistency and control ~ without any wall-hangers to be excused with words or explanations. The resulting work is the only proof.

  

  

  

 

+1 to Russell's post. 

There is a valid discussion to have about the acoustic qualities of various adhesives, but probably not here. This thread is fractured enough. 

I have an old National with a solid Bakelite neck. Even with heavy iron bars embedded inside, it never holds still, changing shape with every change in temperature. Looks cool though. 

Ok. I'm completely confused.

John, if your position is that anything that isn't wood or animal in nature should be replaced, why are you asking about refretting a micarta fretboard?

That was two years ago and my first encounter with a micarta fret board and bridge. I was researching the material and looking for feedback from others. I gave it my full consideration before returning the instrument to its owner without having corrected the lifting or warped bridge (it was not a fret job). I research each instrument before working on it in order to gain advanced warnings of inferior materials or constructions, a practice which protects both instrument and luthier from unwelcome 'surprises'. The internet is useful for this research. If I cannot significantly improve an instrument without undue expense to the owner by having to re-manufacture parts, then it is simply returned. I didn't study the art of instrument building and repair just to deal with plastic replacement parts or try to fill in all the corners that were cut.

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