Re-build Stringed Instrument




Introduction: Re-build Stringed Instrument

About: I'm an industrial designer living in San Francisco.

I found this beautiful (100 year old) mandolin in a junk store in New York City. I took it to a few vintage instrument shops to see what I could find out about it. I was told that the top of the mandolin was collapsing in and that the instrument would be virtually unplayable. Given my interest in making stringed instruments, I took the mandolin to a local luthier who suggested I try to rebuild the body and see if I could get some more years out of it. Glad I did.

Here's how you can restore that old guitar or mandolin that you find in the attic or at a local yard sale.

Step 1: Find the Problem

Notice the crease on the attached photo. The mandolin was collapsing at the point where the bridge rests along the body. After 100 years of tension caused by the strings, it was only natural that the internal structure of the mandolin would begin to deteriorate. I therefore removed the strings and the bridge to release the tension on the body. (Make sure to loosen the strings before cutting them to avoid snapping). I also took off the bridge so the mandolin could rest flatly on its top against my work surface.

Step 2: Remove the Back

Vintage instruments are generally held together by hyde glue. The best way to take them apart is with a little steam and a sharp razor. I dipped a sharp razor blade in some hot water and carefully began slicing away at the glue that fastened the back of the mandolin to its side body. (Take your time and use a bunch of razors. This took me about an hour of careful work)

Step 3: Remove the Broken Braces

Acoustic instruments are typically supported by a system of bracing. Wood strips usually span the width of the body of a given guitar/mandolin so as to prevent the instrument from collapsing under the pressure of strings. After years of use, however, bracings often break or fall off, resulting in compromised body strength. In the case of my mandolin, the bracings appear to have been poorly applied (as was often the case with mass-produced hand-made instruments). With a razor and some more hot water, I carefully removed the bracings from the top of the body, as well as from the back (which I removed in the previous step). Do your best to remove each brace in one piece as you may want to use them later.

Step 4: Cut New Bracings

I measured the width of the mandolin from various points along the inside of its body. The most important area for me to cover was the line at which the collapsing was mostly occurring as a result of the pressure of the bridge. I then found a piece of old, but solid wood and cut it to the width I measured. Notice that I did not yet shape the wood to look like other bracings (this comes later). Using wood glue, I fastened the piece inside the mandolin so it fit snugly in between the sides of the body.

Step 5: Reshape the Top

Using every sort of clamp I could find, I pressed the top of the mandolin (which was where the collapsing was occurring) onto my flat work space. The idea here to to flatten the top and reverse the collapsing of the body. Figure that since it was able to flex downwards, there is also room for it to move back into its original shape. In the case of my mandolin, I applied pressure to the bottom of the instrument (closer to the butt) first and gradually added more pressure closer to the neck over time. Be sure to clamp your instrument on multiple points of each bracing. Let the instrument sit for at least 24 hours. (I think I let mine sit for about two days)

Step 6: Finishing the Bracings

Using sand paper, a razor and a file, I shaped the bracings to make them look a bit more organic. Although they are significantly thinner than they were when initially attached as wood blocks, I left the bracings rather thick so as to ensure the strength of the instrument. This will directly impact how the instrument sounds. For me, having something that played was more important than restoring the original sound. Notice that the crease that originally plagued the top has been reversed.

After banging on various points of the top and determining that the echo and vibrations sounded suitable, I began preparing the instrument for reassembly.

Step 7: Putting It Back Together

I carefully applied wood glue to the back of the mandolin and attached it to the body. I then taped the mandolin with small pieces of masking tape (this shouldn't damage any finish) along the inter diameter of its body applying as much pressure as possible. I then clamped the back to the body and let it rest for another 24 hours. After removing the clamps and tape, I sanded the edges so as to remove all rough points, screwed the tail-piece back on and finally, added a new pair of strings.

Step 8: Play It

Sure, instruments are beautiful as static pieces of art, but really, they are meant to be played. I took this mandolin back to the luthier in NYC who originally guided me through this process and he predicted this mandolin would survive at least another 75 years before needing any more repairs. She sounds great too.



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    13 Discussions

    Thanks, man for being so awsome!!! Got myself a mandolin for 35eur on ebay to find out it was made in 1926 but played and sounded well even with the strings that were already on it. Im playing it for some years now and might want to do something similar to what you did as soon as signs of deficiency show up

    2 replies

    Sweet- what kind of mando? Reach out before you start fixing as I have gathered some new tricks since posting this.

    sorry this post got somewhat lengthy...

    its a flat body like yours, but without the "spiky" shoulders, something pretty close to this: except it really is a mandolin, not a Waldzither. Funny thing was, when i told my gramps, he turned out to have the exact same instrument from the same producer, just from 1938. It was kind of interesting to see how the build at time of the war outbreak had some simpler details what regards metal parts and a fabric cover bag that could have let you think its covering some wehrmacht weaponry... and its string offset was way too much, sounded awful at any fret (before sanding the bridge down ;)

    However the thing i was actually looking for when finding your instructables was whether i could do something to the wood on the outside of the older model to make it more durable against my possibly sweaty forearm and maybe also let it shine a little more too, without hampering the sound or having destructive reactions with the original finish or its residues... do you have some experience regarding this?

    Excellent! I love this kind of project.

    In the main photo in step 3, there appears to be a groove cut just below the middle brace. Am I seeing that correctly? I'm wondering why that cut was there in the first place, as it appears to be the culprit that caused the creasing. Any idea?

    3 replies

    Great eye! I suspect that score was placed there when the instrument was built because at the point where it eventually began to collapse, it was actually once raised up. This was common in this kind of American-made instrument (likely from a Chicago company, but I won't bore you with nerdy instrument history). Basically, where the body once was raised and sloped, it eventually gave to pressure and became inverted. Make sense?

    a chicago company like lyon & healy? they made so many instruments over the years, but now they stick to harps.

    That absolutely makes sense. It hadn't crossed my mind.. that it was done so the top panel could be slightly peaked. My Sherlock skills are not that great, apparently!

    Great project, great documentation. Keep it up!

    Kind of wonder how she sounds. Looks beautiful, if beat up. Not much of a mandolin man, but I'd strum that. :P

    Your bracing looks really thick. While this would certainly add structural integrity, it would also dampen the tone significantly. Have you observed this on your mandolin?

    1 reply

    At the time, I was most concerned with preserving the structural integrity and that's why the thickness is a bit excessive. The tone of the mandolin is still deep and warm, but if I could (maybe I will) do it again, I'd likely make the bracings a bit thinner and more traditional looking


    3 years ago

    I have an old acoustic guitar that's breaking at the base of the neck, I removed the strings but I miss playing her… can anyone help me?

    Awesome. Have an old fiddle without strings.

    I've started using jekyll glue ( it's a monster) as the hyde glue is a little too common man for me. Seriously, this is a great Instructable. Thank you for sharing your project. Well done.