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Martin D-18 Broken Top

7/2010 – This article was featured in a previous FLGR Newsletter. Sign up for free by typing your email into the window to the left and pressing Go!

1.0 Martin d 18 broken spruce top at sound hole.JPG 1.1 Martin d 18 broken spruce top at sound hole.JPG
1. A Broken Spruce Top caused by the hasty removal of a magnetic sound-hole pickup. Since the broken spruce is missing, I’ll have to fabricate and fit a patch. 2. Cleaning Things Up. I’m cutting away the remaining damaged spruce with a jeweler’s saw blade. In order to create a clean looking and manageable glue joint I’m following the grain of the top.
1.6 Martin d 18 broken spruce top at sound hole.JPG 1.7 Martin d 18 broken spruce top at sound hole.JPG
3. A Dremel Tool Circle Cutter is a quick way to route the channels for the inner and middle perfling rings. I’ll cut the larger channel to a slightly shallower radius than needed so I can hand-fit the patch to align with the guitar’s inner perfling ring. 4. Gluing the Perfling I’m gluing some scrap celluloid perfling into the inner channel with solvent cement.
1.9 Martin d 18 broken spruce top at sound hole.JPG 2.0 Martin d 18 broken spruce top at sound hole.JPG
5. Scraping the Perfling flush to the spruce is quick because I already removed most of the protruding celluloid with a block plane. 6. Laying Out the Patch is a simple matter of holding the spruce in place just under the damaged portion of the top.
2.1 Martin d 18 broken spruce top at sound hole.JPG 2.2 Martin d 18 broken spruce top at sound hole.JPG
7. A Coping Saw quickly makes my rough cuts. I’ll leave plenty of material on the inside of the patch so I can match the sound hole with relative accuracy later. 8. Fitting the Patch to the guitar top is an exercise in patience. A really sharp bevel edged socket chisel lets me slowly align the glue joints and the inner perfling rings. After I have a good fit on the edges of the patch I’ll shape the patch so it’s flush to the under- side of the soundboard on the bridge end of the sound hole and flush to the sound hole graft on the neck end of the sound hole.
2.3 Martin d 18 broken spruce top at sound hole.JPG 2.4 Martin d 18 broken spruce top at sound hole.JPG
9. Laying out the Sound hole. I’ve dry-fit the patch so I can transfer the contour of the sound hole to the new spruce. I’m using a shop-made radius gauge. 10. Shaping the Sound Hole. After some coping saw work, I’m sand- ing the patch up to the pencil line with the shop’s Robo Sander and Luthier’s Friend sanding station.
2.5 Martin d 18 broken spruce top at sound hole.JPG 2.6 Martin d 18 broken spruce top at sound hole.JPG
11. Rounding Over the Edge to more or less match the factory’s chamfer of the top around the sound hole. 12. Finish Work. I’ve chosen to finish the patch before I glue it in. This allowed me to tackle some of the other repairs on this guitar’s work order while the finish cured. After sealing with shellac, I used a pre-mixed amber rattle can of lacquer for the tinted coats, followed by a few coats of clear lacquer.
2.7 Martin d 18 broken spruce top at sound hole.JPG 2.8 Martin d 18 broken spruce top at sound hole.JPG
13. Glue Up. I’m using Franklin’s Original Tite-Bond to glue up the patch because yellow glue will do a good job of adhering the spruce to the rossette’s middle ring. 14. Clamping the patch to the rossette is the only clamping force necessary for this glue up. The wood to wood glue joints are compression fit.
3.1 Martin d 18 broken spruce top at sound hole.JPG 3.2 Martin d 18 broken spruce top at soundhole.JPG
15. Reinforcement inside the guitar completes the repair. There are two cross-patches, one at either end of the patch helping to make this a strong and long lasting repair. 16. All Done. The time invested in fitting the patch has paid off. I’ve got tight glue-lines and the perfling ring in the patch matches up with the inner ring of the rossette.