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The Guitar Medic

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Conn F-27 6-string Acoustic Guitar - Repair Cracked Bridge
This Conn guitar had a cracked bridge. It was somewhat 'humped up' just in front and behind the bridge. Typically this means one of two things: 1) the bracing has become detached, or 2) the bridge plate is insufficient to prevent bellying. This can be caused from simple stress, from leaving strings taut on a guitar while storing it away for a long time, wood drying out, or from over-tightening the strings (not using a tuner). So as I examined the bracing I found it intact, but the bridge had pulled upward--still securely attached to the top wood, and had cracked the bridge plate inside under the sound board--weakening it, and allowing the bridge to pull up the top wood. I decided to both reinforce the bridge plate while clamping the top, and then repair the crack in the bridge. The crack appeared to have had a former repair attempted because there was evidence of some type of glue in the crack. Below are photos of the second part of the repair (fixing the bridge crack).
This crack is at a rather odd place. Typically, bridge cracks appear across the pin holes--as a result of the pins pulling forward at that location. This one is at the leading edge of the string slots--indicating that the force of the string pull created this crack at those locations. It could have likely been from someone trying to tune the guitar with old strings on it. Old strings tend to lose their elasticity--and become very brittle. This brittleness dramatically increases the tension when trying to tune to pitch. The potential for damaging a guitar by pulling it out of a closet and trying to tune it to proper pitch only emphasizes the importance of changing strings before attempting to tune a "closet classic" guitar.

7/1/2016 ABOVE - As seen above, a glue-like substance can be seen in the crack--just in front of the bridge pin holes. The crack extends from the 5th bridge pin hole to the edge of the bridge. It is still separated enough to see the glue substance--which appears to have pulled apart.


ABOVE (7-1-2016):  First step was to remove the strings and saddle (just to get them out of the way) and begin digging out the old glue. The crack was wide enough to use the back side of a X-ACTO knife.

ABOVE (7-1-2016):  Here again showing digging out the former glue-like substance.

ABOVE (7-1-2016):  important to vacuum out the debris, to ensure wood-only remaining (and no residual glue). I also magnify (I use a magnifying light) to examine the crack, after vacuumed, to ensure it is all cleaned out. (You can see my magnifying lamp reflection in the pickguard at lower left.

ABOVE (7-1-2016):  Closeup photo of the bridge shows all glue removed, and crack only remaining.

ABOVE (7-1-2016):  I keep ebony wood scraps around for various purposes. One purpose is to "make" ebony sawdust. This can be mixed with epoxy or with cyanoacrylic ('Super Glue") to do a repair of this type. In this case I'll use super glue.

ABOVE (7-1-2016):  Here you can see that I applied the cyanoacrylic, then sprinkled the ebony dust into the crack and onto the surface. It is above the surface, but that is ok, because I will use a razor blade--sort of like a cabinet scraper, to remove the excess flush to the surface.

ABOVE (7-1-2016):  I actually used two hands to do this, but had to use one to operate the camera. Important to keep the razor blade level to the top of the bridge. In this case, to completely hide the evidence of the crack, I got below the "ebonized" finish, and down to the rosewood.

ABOVE (7-1-2016):  Conn bridges on some models are "ebonized". That simply means that they used another material (in this case, rosewood), and colored it black to look like ebony.  Other guitar makers have used this same method. Here you can see that in order to completely blend the repair, I've had to go beneath the ebonized coating.

ABOVE (7-1-2016):  Black shoe dye is perfect for ebonizing. it soaks into the wood, and is completely black.  During the repair process, one of the pearl buttons that cover the screws came out. I put it with the other hardware for later re-installation.  Here you can see that the black shoe dye--which has started to dry, blends nicely. Once a finish is applied, it will match perfectly.

ABOVE (7-1-2016):  I hung the guitar on my wall to let the bridge dry completely. The shoe dye manufacturer suggests 24 hours of drying before applying "shoe polish". I won't be using shoe polish, but I am still waiting the 24 hours. I'll sand this with 400 grit paper, then coat again (if needed) before applying linseed oil.

ABOVE (7-5-2016):  I decided to use wipe-on satin finish polyurethane to further finish the bridge instead of linseed oil. The first coat of the poly still allowed the sanded area to show. But a second coat resulted in the above. I've decided to apply at least one more tomorrow, and probably two. Then it will be time to re-string.

ABOVE (7-12-2016):  I sanded the entire bridge with 600 grit paper to level all of the imperfections. Then I put a coat of satin polyurethane on it. The above shows the finished product. Ready to re-string.

ABOVE 7-13-2016:  Restrung with D'Addario EJ16 Light Phosphor Bronze strings (.012-.053). The guitar sounds amazing and is quite playable.

ABOVE 7-13-2016:  The action at the 12th fret measures just under 1/16"--actually measuring at about 3/64". The frets are in great condition and the action is like butter. It sounds pretty awesome. Pleased to have this guitar.