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Martin Mortise and Tenon Neck Reset

2/1/12 – This article was featured in the Finger Lakes Guitar Repair newsletter. Sign up for the free newsletter today! Type in your email address to the left and press Go.

1_18_12_009.JPG 1.2 martin dx 1 mortise and tenon neck reset.JPG
1. Martin & Co. manufactured this DX-1 in 2006. It has really high action because the neck angle is wrong. The neck angle is wrong because the neck has separated from the body. 2. Neck Joint Failure If the neck is left unsecured, the string tension can seriously damage the guitar. A proper repair will require removal and resetting of the neck.
1.3 martin dx 1 mortise and tenon neck reset neck bolt.JPG 1.4 martin dx 1 mortise and tenon neck reset low action.JPG
3. Martin’s Mortise and Tenon neck joint is held together by glue and a single bolt that is accessible inside the guitar. Since the joint moves easily with light hand-pressure, I know the glue joint has completely failed. I will tighten the screw in order to temporarily secure the neck. 4. Measuring the Action. With the guitar tuned to pitch the action is 3/32” on the sixth string at the 12th fret. If the neck joint had not failed, the action would be fine.
1.5 martin dx 1 mortise and tenon neck reset moderate saddle protrusion.JPG 1.6 martin dx 1 mortise and tenon neck reset score heel.JPG
5. Measuring the Saddle protrusion above the bridge. Al- though when secured, the neck angle is functional, the geometry of the guitar has changed as a result of 6 years of string tension. While I have the guitar apart, I will adjust the neck angle. 6. Scoring the Heel “Cap” will determine my final, maximum depth of cut when I refit the neck. My calculations dictate that .035” is the correct amount of neck material to remove in order to obtain an ideal neck angle.
1.7 martin dx 1 mortise and tenon neck reset heat fretboard extension and remove from top.JPG 1.9 martin dx 1 mortise and tenon neck reset remove neck.JPG
7. Removing the Neck happens in a similar fashion as a typical Martin dovetail joint. I start by heating up the fretboard tongue with a heat lamp. Once the glue is soft my offset artist’s spatula severs the glue joint. Since the glue joint has completely failed, there is no need to steam this neck joint. 8. With the Bolt Removed I applied light downward pressure on the fretboard and the neck easily pulled free from the body.
2.0 martin dx 1 mortise and tenon neck reset not enough glue.JPG 2.1 martin dx 1 mortise and tenon neck reset cracked tenon at threaded insert.JPG
9. The Tenon is the part of the neck milled to fit inside of the neck block’s mortise. Not enough glue was used at the factory which probably contributed to the neck joint’s failure. 10. The Neck is made of stratabond, a high tech plywood of sorts. Because the glue- joint failed, an excessive amount of string-tension was concentrated on the bolt and threaded insert. This caused the tenon to de- laminate. I’ll fix this crack later.
2.2 martin dx 1 mortise and tenon neck reset sand heel cap.JPG 2.3 martin dx 1 mortise and tenon neck reset relief cut heel.JPG
11. Sanding the Heel “Cap” to the scribed line with 80 grit sand- paper establishes my maximum depth of cut. 12. Back Cutting the Heel with a sharp chisel will make it easier to make a gap free transition from the neck heel to the guitar sides.
2.4 martin dx 1 mortise and tenon neck reset cut heel.JPG 2.5 martin dx 1 mortise and tenon neck reset glue and clamp cracked neck tenon.JPG
13. Trimming the Heel establishes the new neck angle. I will make a series of cuts that will remove .035” of neck material from the heel cap tapering to no material loss where the heel meets the fretboard. A sharp chisel does most of the work followed by a few pulls of 220 grit sandpaper through the joint with the neck dry-fitted onto the body. 14. Repairing the Cracked Tenon. I used super glue and a moderate amount of clamping pressure to repair the delamination. Now I am wicking some glue into the strat- abond around the brass insert. A q-tip prevents the threads from getting gummed up with c.a.. Epoxy would also work well. I’ll leave the tenon clamped overnight.
2.6 martin dx 1 mortise and tenon neck reset fabricate shim.JPG 2.7 martin dx 1 mortise and tenon neck reset refit tenon.JPG
15. Fabricating a Shim to tighten up the neck joint. A block plane makes quick work of the mahogany. 16. Refitting the Joint doesn’t require much more than removing the old glue and some light paring with a chisel in order to get a tight fit between the mortise and the tenon.
2.8 martin dx 1 mortise and tenon neck reset glue stratabond neck.JPG 2.9 martin dx 1 mortise and tenon neck reset glue and clamp neck.JPG
17. Gluing the Neck. Normally, I prefer to use hot hide glue for neck resets, but aliphatic resin glue does a better job of gluing the plywood neck block and the stratabond neck together. 18. Clamping the Neck while the glue cures for 24 hours. A cork-lined clamping caul protects the underside of the top from the c-clamp and a radiused maple block distributes the clamping pressure. The bolt must be re- installed in order to help draw the joint together during gluing.
3.0 martin dx 1 mortise and tenon neck reset low action.JPG 3.1 martin dx 1 mortise and tenon neck reset plenty of saddle protrusion.JPG
19. Low Action as measured at the 12th fret. 20. Plenty of Saddle protrusion above the bridge: twice that of the 6th string’s action as measured at the 12th fret. The neck angle is ideal.
3.2 martin dx 1 mortise and tenon neck reset back together.JPG
21. All Done. There is no obvious hint of repair. The heel matches the contour of the sides and the fretboard tongue is securely glued to the top.