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The all-too-common
F-Hole Crack
© Frank Ford, 11/22/02; Photos by FF

It's a 1952 Epiphone Triumph, and it's in fine shape except for a small crack in the top.
The crack is in the most common location, right at the f-hole. It doesn't take much of a hit to crack a solid top guitar here.
The first order of business was to glue up the crack. I chose hot hide glue because it's plenty strong and rigid, but mostly because it is the least likely to stain a blond spruce top. Flexing the crack open, I was able to work in lots of good glue.
A bit of cleanup with warm water.
To clamp the crack closed, I chose a small pine wedge, which I inserted into the f-hole where it was a bit wider, and slid downward to the point. That generated plenty of sideways pressure without distorting the top as it might have if I had simply shoved the wedge straight down.
I used a piece of flexible celluloid as my top caul for leveling the crack through its length.
First, some waxed paper to keep the caul from sticking
Then the flexible caul and some light clamping pressure to hold the crack level as the glue dried.
I used three of those little violin clamps.
Here's where the fun started. I dunked some Friendly Plastic in hot water.
And, it became clear and pliable. If you don't know this stuff, you should get some from L.M.I.. It's completely reusable, and very friendly indeed.
It's soft at 135 degrees Fahrenheit and rigid as polyethylene at room temp. I molded a hunk to match the curve over the crack, using a bit of aluminum foil to protect the finish.
Then, when it cooled, I had a perfect little rigid block that exactly matched the curvature of the top.
I made up a little spruce reinforcement cleat to keep the crack from cracking open if it got leaned on again.
And, holding some sandpaper on my new curved block, I was able to sand a matching curve into the gluing surface of my new reinforcement. While the inside may not have been precisely the same curvature as the outside, I figured it was damn close, so the plastic made a good contour block for this job.
A drop of cyanoacrylate on my clamp, and a drop of catalyst on the wood patch, and I was good to go.
Holding the patch on the clamp at the correct angle, the glue set instantly so I could insert the clamp and patch right where I wanted it.
Some aliphatic resin glue on the patch. I could have used hide glue here too, but I figure the aliphatic resin is more likely to adhere to the old interior spruce surface without any special preparation. Hide glue doesn't like old oxidation.
And, right inside it went. The cyanoacrylate bond is just enough to hold a patch to the metal clamp, so I knew it would be very easy to break the clamp off without disturbing anything once the wood joint had cured.
And, that piece of Friendly Plastic made the perfect exterior caul, of course.
All done, and solid. No touchup this time because the rest of the guitar is loaded with little scratches dings and wounds, so I didn't want this area to look out of balance.

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