Repair Services

This mandolin showed evidence of a failing neck joint. In order to diagnose the problem and repair it, the neck had to be removed. Here is how I went about finding the problem and deciding how to fix it. Click the thumbnail images to see larger images.

There was cracking of the lacquer along the sides of the neck heel where it joins the body, and there was a gap between the heck heel and the heel “button” of the back. The neck joint was obviously failing.

Someone in the past had added a metal dowel through the heel button and into the neck heel. I sawed through it with a razor saw in order to be able to remove the neck from the instrument.

To expose the neck joint for access, the fingerboard had to be removed. I used an iron to heat and separate the glue joint while shielding the mandolin from the heat with foil-covered cardboard.

With the glue softened by the heat, I used a putty knife to separated the joint and cleanly remove the ‘board. This is a fingerboard that I had put on this mandolin some years ago when it needed a broken truss rod replaced, so I knew what to expect when releasing the joint.

The neck movement had started to sheer the glue joint between the top and the fingerboard extender and it popped off when the fingerboard was no longer holding it in place. Here it is flipped over to show the underside. You can also see the dovetail neck joint.

Here’s my steam source; an espresso maker; injecting steam into the dovetail joint to release the glue.

Here is what I found in the neck joint. There were some repaired cracks in the head block with some small dowels, and an assortment of shims used to tighten the dovetail because it didn’t fit well.

With all the shims removed, the dovetail mortise in the head block was huge. The remaining wood to the sides of the mortise was thin as a result, and there was not a lot of strength.

Some of the shims stayed behind in the mortise and some stayed on the neck heel during the neck removal.

The neck heel had a cap on the end to make it large enough to fit the mandolin, and the shims were all above the cap so that when they were removed the cap was left overhanging. I later trimmed the cap even with the dovetail.

Here is most of the stuff I got out of the dovetail. (I probably lost a little of it.) The shims were simply stacked and wedged in to tighten the fit, not fitted and glued securely for a solid structure.

I decided the head block needed to be rebuilt to have more strength and to make the mortise smaller so that it more nearly match the size of the dovetail tenon of the neck. By making the mortise smaller, I could leave more wood in the block to each side of the mortise and increase the strength of the block.
I started by removing the split and damaged wood of the block and then cut a cavity with flat sides, tapering the sides so that I could tightly fit in a new piece of wood.

I cut a piece of scrap mahogany to fit into the head block…

…and chalk fit it into the tapered cavity. The white chalk you see is applied to the cavity and it transfers to the filler piece when it’s placed in the cavity…

…indicating where there is contact.

By repeatedly cutting away wood where there is chalk transfer, a good fit can be attained for gluing. When the fit is good, the block goes all the way in and there is chalk transfer nearly everywhere.

I cut away most of the excess wood of the block, put it in place and drew the dovetail on the block.

I cut the dovetail with a dovetail saw so that the neck would start in, but not too far. I needed to be able to fit the dovetail to align the neck to the body later, so I didn’t want the fit too deep at the start of that process.

Here’s the block, fit into the cavity, the dovetail cut and ready for glue.

The chalk is cleaned off of the wood and the glue is applied and the piece clamped in position. The new piece was left thick so that the top surface sat above the old block so that it could be clamped firmly.

After the glue cured, I shaved away the extra wood to level the top of the block…

…and also shaved away the extra wood here to reestablish the shape to the original contour.

The rebuilt head block looks like this. I oriented the grain of the filler piece this direction to make the “wings” of wood to the sides of the dovetail stronger than they would be if the grain matched the direction of the head block.

The mortise in this little piece is still the same size as it was and no longer matches the head block…

…so I fit a piece of maple wood into it…

…glued it and trimmed it down to size…

…then cut the dovetail into it…

…so that it nearly matched the dovetail in the head block.

…then glued it and cut it the rest of the way.

When I started fitting the neck into the rebuilt head block, it turned out to be off center, so I securely glued a mahogany shim to one side of the dovetail to center the neck on the body…

…and proceeded to fit the dovetail in the usual way, chalk fitting for good glue surfaces.

When the fit was good, I glued and clamped the dovetail to attach the neck.

Here, the neck is glued back in position but the finish has suffered some damage from the failure of the old joint…

…and the new wood shows on the scroll side of the neck heel.

I re-glued the fingerboard extender. Two small dowels held the tapered caul so the clamp aligned with the back of the mandolin and did not slip out of position. The taper of the caul also directed some of the clamping force so that it held the extender tightly into the corner where the binding cross piece is.

I prepared the neck surface and fingerboard surface for gluing…

…and glued and clamped the fingerboard back in place, using two alignment pins and a thick clamping caul. The two missing frets in the picture are where I put the small brass alignment pins through the fret slots. The pins were then pulled out and the frets replaced.

With the structural repair done, I touched up the color…

…and the lacquer wherever there was damage from the neck joint failure or from the repair.

When the lacquer repairs were done and cured, I level sanded and buffed…

…and strung the mandolin up, hopefully for many years of reliable use.