Headstock Crack Repair - Backstrap Method
By Steve Carmody c. 2015
Recently, a customer brought me a Gibson vintage reissue J-45 with a nasty headstock crack. Many Gibson necks are very
slim in the area of the nut. Additionally, the truss rod nut access is at the base of the face
of the headstock, directly behind the nut and the wood is scooped out in this area.
As a result, the wood in this part of neck is quite susceptible to cracking if the
headstock is bumped hard enough.
The key indicator of potential long-term success when repairing a damaged headstock is a
having a nice long gluing surface. So, from the repair point of view, the ideal crack runs
from behind the first fret
and radiates up to area of the E string tuning machines. With two long flaps of wood
you can have a stable, strong glue joint. Indeed, some guitar necks are
constructed from gluing together multiple pieces of wood and the headstock is fashioned
by joining together two pieces of wood in what is called a scarf joint, which features a long flat gluing
surface between the two parts. The worst case scenario from the repair point of view, is when
the neck just snaps and the two parts just butt together. That is what had happened to
the guitar that had been brought in to me.
In a case like this one, if you simply butt the two pieces of wood together and glue them,
the joint will never hold
against the tension of 6 guitar strings. But if the guitar is worth the effort it takes, there
is a method of successfully repairing
a nasty crack such as this.
In the picture below you can see the crack. I have done the initial gluing but you can see
that the neck essentially snapped directly behind the area of the nut and the two parts just
butt together. As it is, there is very little strength in this glue joint. To renew the strength in this area I
will fit and install an overlay of wood ( mahogany in this case, the same wood as is used in
the rest of the neck) which will overlap the crack. This is called a headstock backstrap. Some luthiers use
a backstrap, or a multilayered series of backstraps, to add strength to newly constructed necks. But
in this case the backstrap will serve to renew the strength of the broken neck.
With my freestanding beltsander, I sanded off about one-eighth inch from the neck and back
of the headstock area. I tapered the sanded area at either end and it is deepest ( about an eighth
of an inch) right where the crack is. The green tape gave me a general guide of how far in
either direction I wanted to sand. Next I cut and sanded a piece of mahogany to match the curvature
of the back of neck in the area where I sanded. This was done by eye, with repeated checks
of the fit to the neck, on the belt sander. Some luthiers will take a pre-thicknessed veneer
of wood and bend it to fit, but I decided to fit a solid piece of wood to the neck. Regardless of
how it is fabricated, this additional piece of wood is going to add strength to this part of the neck.
Once the curvature of the backstrap patch was fitted to the sanded area of the neck,
I reduced the outer size of the patch until it was just slightly
larger than the sanded area on the
back of the neck.
The picture below shows the various clamps and cauls used to glue the backstrap to the neck.
Once the backstrap was glued on, the excess wood was brought down to match the shape of the
neck and headstock with a coarse rasp, files and finally sandpaper. In the pictures below you
can see that the backstrap has been glued and fitted. Note that the strap extends a few inches above
and below the area of the crack.
Then the grain is filled and sanded smooth. Multiple coats of sanding sealer, tobacco brown
colored laquer and then top coats of clear laquer are sprayed. After the finish has cured for a couple weeks,
it is polished out and the tuners installed. In the end, thanks to the fact that the neck is
very dark tobacco brown, the repair is invisible.
Steve Carmody is an independant guitar repairman and luthier with a shop in Silver Spring, Md.
He has been doing guitar repair and restoration full-time since 1990.
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