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bridge replacement - glue directly to bridge plate?


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so, a few days ago i replied to an add for a "beginner japanese guitar" because i was looking for a deal on a hard case for another guitar of mine. $30 for a case is a good deal, right? free "beginner japanese guitar", too. score.

i didn't even look at it when i was at the guy's place. i haggled him for some free picks (he didn't have anything thicker than 1 mm.)

but, when i got the guitar home, i realized it's a solid body takeharu guitar built in 1971. yeah..

i know it's solid body due to the grains, and also due to the soundboard.

unfortunately, the bridge was falling off and it looks like there was some repair to the cross-section underneath. but, whomever tried to glue the bridge on seems to have done so very poorly - and repeatedly. it was clear from the start that he used some kind of crazy glue, but when i got the bridge off i actually found three different types of glue on it, none of them applied very well. i'm guessing that the crazy glue was try number three, and it doesn't look like it was ever clamped. yeah. so, i'm hoping that if i just glue it back on right with the right kind of glue and a good clamp it should sit tight. the operative word is hope - this is a 50 year old guitar, and i don't know exactly what's been done to it or what's wrong with it.

the guitar appears to be a martin copy with a solid spruce top with lines running parallel to the strings. but, when i took the bridge off, i took some wood with it (damned crazy glue.) and it seems to have uncovered some kind of secondary piece of wood underneath the bridge. now, i'm imagining that this was put there as reinforcement, but i don't exactly understand why.

if i look carefully underneath this wood, i can see some grains running in the right direction, so i'm tempted to just rip the layer off and glue directly, even without knowing why it's there. but, i'm concerned that it might be the plate rather than the wood.

if i pull my hand underneath and feel around, i'd guess that the width of the plate is too thin, and it must be the body. but, that's just intuition...

i've been playing guitar for a long time, but i only do repairs when i have to, and i'd appreciate running it by somebody. what do you think - did i hit the body underneath some kind of added plate, or the plate underneath the body, as i was scraping?

1) wood peeking out:
https://drive.google.com/file/d/17KKkfjqcd2tY8oXL91FO82ZykmT-XC1D/view?usp=sharing

2) soundboard:
https://drive.google.com/file/d/1mzLm5eLqCuJbCOB0fUw3_q9QXVhhAStU/view?usp=sharing

now, if i've hit the body, i'm going to scrape the wood off and glue it flush.

but, if i've hit the plate, what's the better idea here? if the logic is that this is worth saving because it's solid body, is pasting some kind of plate in going to defeat the purpose? further, if i'm concerned about action on an old guitar like this, wouldn't it be better to keep it lower and just glue it to the plate, anyways? is that structurally terrible, or just merely inadvisable?

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6 minutes ago, deathtokoalas said:

the guitar appears to be a martin copy with a solid spruce top with lines running parallel to the strings. but, when i took the bridge off, i took some wood with it (damned crazy glue.) and it seems to have uncovered some kind of secondary piece of wood underneath the bridge. now, i'm imagining that this was put there as reinforcement, but i don't exactly understand why.

It's not a solid Spruce top, it's a Plywood top from what I can see.

The top ply came off with the bridge and you're seeing the next ply under it.

The plys in plywood always run cross-grain to each other, that's what gives it its strength.

Most budget acoustics use Plywood, its nothing unusual.

You only get real solid Spruce when you get into the upper price brackets.

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I agree with Drak.  That is a plywood guitar.  It still could be a decent instrument.  You have lost the thickness of one ply which may or may not be a problem.  To fix this you need to clean off all the existing glue on the bottom of the bridge as well as on the guitar.  You also have to remove all of the wood sticking to the bottom of the bridge.  Then place the bridge on the guitar and use a straight edge along the string path to see if you can still get decent string height.  You may have to replace the saddle with a taller one but if much more than half the saddle height is above the slot you can have problems. 

There should be a reinforcing bridge pad under the top.  Use a mirror to make sure it is in good shape.  If all checks out I would glue it up with Titebond or other good wood glue.  Normally I like hide glue but Titebond has better gap filling for this one.

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Yepp, that looks like plywood.

What's not so nice is that the top layer should be there for strength - no matter how thin the top layer is, adjacent long fibers going length vise under the bridge can resist the string pull much more than traverse grain. I've got a classical guitar with a similar problem, the top layer has been removed at some point to clean the surface for gluing and the two layers left are so soft I can poke my finger through! Luckily steel string acoustics often have a piece of hardwood called the bridge plate supporting the pins so if there's none you should "easily" be able to make one.  The grain direction of a bridge plate is traverse to the top.

Hint: You can see what's inside by taking a couple of photos with your cell phone, using the self timer feature and flash.

The only way to really strengthen the top would be to peel the entire length of the top veneer from the sound hole to the bottom of the lower bout and replace the top veneer. Such a repair would be insane!

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this is not a budget or factory built guitar, it's a custom built guitar from 1971. these guitars were made of solid wood, and i've seen listings for them on reverb for over $5000, although the average price is $500-$1000. there were roughly 10,000 of them made between 1970-1980. you might not have heard of takeharu, but he's as well known in japan as jimmy page would be in western europe and the united states. 

that said, i agree that it looks like plywood, which  is what's confusing me about it. and, if the consensus is that it is plywood, then i'm left to conclude that somebody must have swapped out the top, which is making the value of trying to fix it seem dubious..

i don't think what's under the ply is more ply, though - it seems to have a single piece of wood underneath it.

i tried to tune it up normally before i took the bridge off and the action was unplayable. i don't want to reset the neck, and it doesn't look warped. so, what's the worst thing that can happen if i just carve the plywood out and glue it to the piece underneath it, to try to keep the action low without messing with the neck?
 

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I don't know where you live, but if you have any guitar repair shops around, make an appointment for an estimate.

Estimates are (usually) free, and you can find out what the true assessment is for the guitar.

Right now, you're just guessing at it. We can play the guessing game all day long and just go 'round in circles.

Take it to someone who professionally repairs guitars and gets paid for it to give you a real-time analysis of what you have.

If the guitar is as valuable as you think it is, they'll tell you what it needs.

If you want to do it yourself, you'll at least be armed with accurate information from an experienced pair of eyes who held it in their hands.

Any truly valuable instrument is easily well-worth a trip to a real doctor for a real evaluation.

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i think you're half right. i mean, i'm not looking to sell this guitar - i want to play it. i don't really care what it's worth (and i overcarved the finish to make sure i'd get enough wood, so i don't care what it looks like, either). but, if i had somewhere to take it with people i could trust, i'd take it there.

the only option i have is a long and mcquades, and i think i trust my own analysis better than theirs.

on top of that, i'm expecting kind of the same reaction, which is how i ended up with it. japanese name. not recognized. therefore, budget. but, that's not actually true, and the likelihood i'll find somebody that realizes it is fairly low.

so, let's ignore the price of the guitar and get back to the physics of it, which is why i came here.

if the back plate is solid, and i glue it properly with good clamps, is the idea of gluing it to a lower piece of wood to keep the action down without messing with the neck a catastrophic error or merely an inadvisable risk?

Edited by deathtokoalas
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To find out what you have under the bridge is to look somewhere where the wood has been cut, in this case it's the peg holes. Take a torch and a magnifying glass and look all around the hole. If you see uniform layers all the way down all around the hole, it's plywood. If you see end grain at opposite sides of the hole, there's solid wood. If you see upright stripes all the way down, they're vertical growth rings which means it's quarter sawn solid wood.

If you need to, roll a piece of sandpaper and try to smoothen the hole just to clean any furry stuff. You don't want to enlarge the pin holes!

If you don't have a good enough magnifying glass, use your cell phone camera. Use flash and other light sources and macro mode if applicable. Try to focus as well as humanly possible. The two photos you linked to are blurry and blurrier much due to insufficient light. Use sunlight, mirrors, white paper, torches, flashlights, desk lamps, whatever to get more light into the holes for the sharpest photos possible.

I highly recommend you to look at Jerry Rosa's guitar repairing videos, he's got quite a many of them. This is a short introduction to the subject:

 

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that obvious suggestion actually helped quite a lot. thanks.

i should point out it has action holes, first. this is a 1976 version (i know mine is 1971 from the serial number, 01022) here and you can see the old 60s style action screws:

ngcb1

so, when i look through the action holes, it looks like solid wood - despite the ply-looking exterior. 

but, when i look through the string holes, i can see the bridge plate, what seems to be a second bridge plate as reinforcement and a third layer, in addition to the top ply. so, there's two layers of bridge plate and two layers of top....on the string holes.

further, you can tell by looking at the wood that the string holes are way newer than the action holes.

so, i'm left to conclude that this guitar has already had a lot of work done...and i could probably find the cut if i scraped enough...

...but i'm not going to tear that wood off, then; i still have the fibers on the bridge, and i'll be careful to sand around it before i reglue it. that means action might be a problem.

what i'm going to do tonight is try to figure out what kind of shape the neck is in, before i invest in those clamps and that glue.

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16 minutes ago, deathtokoalas said:

i'm left to conclude that this guitar has already had a lot of work done...

If it wasn't you who cut and ripped the spruce layer off from under the bridge I'm tempted to agree.

There's many ways to clamp the bridge, you don't necessarily need the dedicated long reach clamps through the sound hole! The easiest solution is to put a snugly fitting block inside the guitar and clamp from the outside. Even there you can use a couple of 2x2's across the top and bottom and tie them with a bungee cord, using small wedges for tightening the bridge against the top.

The action being high may be due to a common problem with acoustic guitars: The strings pull the bridge area up and the braces slowly give in to the new shape.

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when i first got that plate off, the body was just gobbed with all kinds of glue. there was a yellow glue that might have been the right type, but was applied in little dabs in the corner, there was a more liberally applied white glue and there were gobs of crazy glue applied in thin lines. i scraped as much off as i needed to scrape off the glue, but i was careful, and i don't think i scraped off more than i could have avoided.

the places i circled in red are still on the bridge, and i don't know if the previous removal(s) took wood with them. 

but, i realized quickly that the finish was interfering with the glue, which may have been why somebody tried crazy glue. i wanted to be extra sure, so i cut it a little bit extra. at least in the places i cut, the wood is basically the same as what was already there. but, there's two reasons that's weird. first, these were handmade guitars - it's weird that they'd have that kind of factory defect, unless it was recently redone. second, it would suggest that if a spruce layer was removed then it was removed a good ways around the bridge. there's a minor bulge under the finish just above the string holes, but nothing otherwise suspicious.

the person that sold it to me was an older japanese fellow who received it from "a friend". he knew the bridge was "worked on", but couldn't provide further details. his kijiji site has several high-end guitars for sale, so i think he's withholding information. but, like, i can't torture it out of him - it's not world war two, anymore. if he's not talking, he's not talking. and, i don't have 20s to feed him, x-files style.

as the plate wood looks far newer than the top wood,  i'm thinking it must have been reinforced and maybe rebuilt from the bottom. there must have been a reason for that.

i don't want this to come off again, so if i'm going to bother doing it, i'm going to do it right ,with big clamps.

Edited by deathtokoalas
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There's also light steel strings. "silk'n'steel" if memory serves me right.

I highly recommend viewing a bunch of Jerry Rosa's guitar fixing videos. They're lengthy but contain lots of solid information. What I specifically like about them is that he's not the ADHD guy bouncing back and forth doing all fancy video tricks.

2 hours ago, deathtokoalas said:

if i'm going to bother doing it, i'm going to do it right ,with big clamps.

Understood. That said, the inside block and 2x2's tied with bungee cord and adjusted with wedges is a right way to do it. It's not how the professionals would do it but buying all the equipment for one time use when the result still remains unsure may not be economical. I've also seen a video about extending the reach of regular F-clamps for such purposes. There's many ways to skin a cat...

 

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so, i've decided the neck is healthy enough to keep going. it's not curved upwards, but rather curved at a nice 30 degrees downwards. it may need a truss rod adjustment, but let me get the strings back on first.

i think that putting four c-clamps as is standard is dangerous for the bridge, so i want to use something like this instead:
https://www.wish.com/product/5e22c9b8ad036d0f44099295?hide_login_modal=true&share=web

it seems normal to add a c-clamp on top of it. but, is that really necessary or is it overkill, especially if i'm concerned about the tension?

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59 minutes ago, deathtokoalas said:

i think that putting four c-clamps as is standard is dangerous for the bridge

Think again. The long reach c-clamps that you install through the sound hole are designed to push the bridge plate, top and bridge together. There's only wood and glue involved so you can't tighten them enough to really break something. The only thing to worry about with them is scratching and that can easily be avoided with pieces of leather.

Obviously you can't clamp from outside of the body i.e. push the top and bottom together but you can apply all the pressure you need if there's solid materials all the way between the clamp jaws.

You can easily build a similar tool out of a block of wood and a couple of bolts and wing nuts. It's just an adjustable counterpart for the bridge. The outermost black handle screws are for fine tightening the ends of the bridge but small wedges work just as well or even better. The wing nuts are for tightening the bridge and I'd definitely use large washers or rather a fitting piece of plywood against the bridge plate to avoid the bolts coming through the top! - The reason to use a c-clamp on top of such bolt-on tool is to add enough pressure.

kuva.png.d50b296b06a6e251394fc2e4277bfe50.png

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