As published in the IPCI Book.
One of the traditional methods employed to repair cracked pegbox wall consists of removing half the thickness of the pegbox inner wall over the crack area, and then fitting one or two reinforcement pieces, or clavettes, made of cross-grain maple.[1] Invasive and time-consuming, this method not only requires a fair amount of touch-up but ultimately is susceptible to failure due to the difference in expansion and contraction of maple across the grain and along the grain.
The method I developed consists of inlaying the pegbox inner wall with a carbon-fibre bushing (ring) around a peg hole after the crack is cleaned and glued. Significantly less invasive than clavettes, a carbon-fibre bushing (ring) reinforces the pegbox wall around the crack and requires very little touch-up. Moreover, carbon-fibre is not susceptible to changes in humidity.
Due to the nature of the material and the fact that it is not readily visible, this repair should be documented.[2]
MATERIALS AND TOOLS
– a temporary, loose-fitting maple bushing
– a custom hole saw about 4 mm larger than the diameter of the peg hole (The one shown here has a 12-mm outside diameter and a 0.5-mm wall thickness.)
– a drill bit that matches the arbor of the hole saw (Here, I use a 3-mm bit.)
– a custom mandrel made to fit the hole saw.
– a chinrest tool
– a custom nylon jig (The inside part of the jig should match the inside diameter of the hole saw; the two outside halves should match the outside diameter.)
– carbon-fibre strands long enough to wrap around the jig three or four times, like lapping.
– epoxy
– a wide elastic band
– a lathe
– a chisel, gouge or knife
– black watercolour paint
PREPARING THE PEGBOX
Clean and glue the pegbox crack.[3]
Place the temporary bushing into the peg hole to be reinforced. It should fit loosely. Do not clean or ream the peg hole beforehand – the temporary bushing will later be removed and the original peg replaced. Glue in the bushing.
Insert the drill bit into the opposing hole and drill a guide hole the size of the end of the mandrel in the center of the bushing.
Insert the hole saw into the pegbox, cutting side toward the peg hole to be reinforced.
Screw the mandrel into the hole saw.
Place the end of the mandrel into the guide hole, and carefully cut a ring around the peg hole halfway through the thickness of the pegbox wall.
To release the hole saw from the mandrel, fit the chinrest tool into one of the small holes in the saw, and turn in the opposite direction. Remove the mandrel and hole saw.
MAKING CARBON-FIBRE BUSHINGS
It is necessary to make these bushings because the carbon-fibre strands must run circumferentially around the prepared ring, and I have yet to find a carbon-fibre product that does this.[4]
To make the bushings, select a strand (consisting of dozens of fibres), coat it with epoxy, and then wrap it three or four times around the inside portion of the nylon jig, like lapping. Repeat with more strands to make a tube.
Clamp on the outside part of the jig with the rubber band and set aside to cure for approximately 8 hours.
Remove the outside portion of the jig. Cut the carbon-fibre tube into individual bushings.
FITTING THE BUSHING INTO THE PEGBOX
Select a bushing and place it into the prepared ring. Once you are sure of the fit, glue the bushing into the ring with epoxy.
Let cure for approximately 8 hours.
Cut down the bushing with a chisel, gouge or knife.
Touch up the inside of the pegbox wall to camouflage the bushing, and then varnish.
Remove the temporary bushing and replace the original peg.
Notes
1. In extreme cases, cheeks are fitted to the pegbox outer walls. BACK TO POST
2. Cross-reference Vol. 1, “Documentation,” Barclay’s article in particular. Ed. BACK TO POST
3. Cross-reference article(s) on cleaning and gluing (pegbox) cracks. Ed. BACK TO POST
4. Since the publication of this article, we found a manufacturer and we sell carbon-fibre bushings. BACK TO POST
Pasewicz, Jerry. “Reinforcing a Cracked Pegbox Wall with a Carbon-fibre Bushing.” The Conservation, Restoration, and Repair of Stringed Instruments and Their Bows. Vol. 2. Montreal, London: IPCI-Canada, Archetype Publications, 2010. Print.