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Repairing Acoustic Body Cracks: 1931 Martin 0-18T Restoration and Repair, Pt. 6

I decided to do some body repairs before I reattach the neck on the 0-18T,  It's a lot easier to handle the body alone without the neck attached.

There's a crack on the lower bout on the bass side of the body. As it turns out, someone had previously squirted some glue in the crack, but I wanted to back up the crack with a cleat.

The sides are mahogany, so I used a piece of mahogany for the cleat. I cut a small rectangle and traced the curve of the side onto it. Then I cut the piece on the bandsaw, following the curve, then I thickness sanded it on the ROSS.

The sides of the guitar are quite thin - about .050 of an inch or about 1.27mm. So I sanded the cleat to be just about that same thickness.

I also sanded some small chamfers on the edges of the cleat (the arrow points to one).

Here's the cleat lying on the outside of the body near the crack.

Since it's thin and light, the cleat will flex and follow the shape of the side when it's clamped in place.

The problem now is how on earth to get the cleat in position? I can't reach the crack by hand from the inside.

After a couple of failed attempts trying to tape the cleat to long needle nose pliers which were too clunky, I came up with this approach.

I put a small pin into the cleat, then used my parts grabber claw tool to hold onto the pin.

It worked well.

I put a piece of masking tape under the crack so I'd have a visual reference as to the crack's location.  Then I lined up the bottom of the cleat with the kerfing - the crack was right above it.

Then I used a pair of repair magnets to hold the cleat in place.

It was during this process, with a light inside the guitar, that I clearly saw some glue that had dribbled down onto the kerfing - where the previous repair was done. I'd guess the repair person realized the crack was virtually impossible to get to.

It's not a bad repair, but this cleat is an improvement.

Look at how well made the bracing is - not a bit of glue squeeze-out or sloppy work to be seen. The craftsmanship on these old Martins is something to emulate when doing repairs or building new instruments.

There are also three cracks on the upper bout on the treble side of the guitar. I used the same approach to this repair.

The curve here isn't as pronounced, but the cleat does have a slight curve to it.

Note that the grain of the cleat is also perpendicular to that of the side, which will add strength to the repair.

All three of the cracks are quite tight, but I was able to open the topmost crack a tiny amount. I put a pin in the opening in order to spread hot hide glue into it before I put the cleat on the inside. I like to get glue into the crack if possible.

Since the sides are so thin, the edges of the crack want to break up - we have to be gentle opening the crack this way.

This cleat was much easier to install.

I taped the top neodymium magnet to the cleat, put glue on it and put it in place inside the guitar.

Then I put a mating magnet on the outside, and then put another pair of magnets to hold the bottom of the cleat.

This is what the magnets on the outside look like.

These things are fantastic for these kinds of jobs. They're incredibly strong - you need to be careful that you don't pinch you fingers if you let 2 of them get near each other on the bench!

Next I'll make a new pickguard and (finally) put the neck back on.

All posts in the 1931 Martin 0-18T Restoration Project:
  1. 1931 Martin 0-18T Guitar Restoration and Repair, Pt. 1

  2. Neck Removal on 1931 Martin 0-18T Guitar: Restoration and Repair, Pt. 2

  3. Trimming the Neck Heel for Reset: 1931 Martin 0-18T Restoration and Repair, Pt. 3

  4. Shimming Guitar Neck Dovetail and Finish Chip Repair: 1931 Martin 0-18T Restoration and Repair, Pt. 4

  5. Caul for Heat-straightening Guitar Neck: 1931 Martin 0-18T Restoration and Repair, Pt. 5

  6. Reparing Acoustic Body Cracks: 1931 Martin 0-18T Restoration and Repair, Pt. 6 - This page.

  7. Making a Tortoloid Pickguard: 1931 Martin 0-18T Restoration and Repair, Pt. 7

  8. Heat Straightening Bowed Guitar Neck: 1931 Martin 0-18T Restoration and Repair, Pt. 8

  9. Fret Marker Installation and Filling Fingerboard Chips: 1931 Martin 0-18T Restoration and Repair, Pt. 9

  10. Compression Fretting to Correct Upbow: 1931 Martin 0-18T Restoration and Repair, Pt. 10

  11. Completed 1931 Martin 0-18T: Restoration and Repair, Pt. 11


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