Author: Gordon (NZ)
Date: 2004-05-30 14:20
Depending on the nature of the damage:
1. The chips can be glued back where they came from, probably using an appropriate type of cyanoacrylate ('super-', or 'CA') glue.
2. The chipped area can be filled with a composite built up from an appropriate CA glue and grenadilla 'chips' (actually more like dust).
3. In the past I have had excellent success building up such areas with epoxy glue (with black pigment), incorporating thin stainless steel reinforcing wires (i.e. needle springs) inserted (axial &/or circumferential) as appropriate, using holes drilled into the good timber, in the same manner that a dentist may reconstruct a broken tooth with pins and composite material. I have not heard of other technicians using this technique. For me, this has never failed.
4. Grafting - a traditional and reliable approach. The entire tenon is removed, and a socket bored out (using a lathe &/or a specialised tool) of the end of the body, to receive a new tenon that is turned to shape and glued in. Such a job, done with all dimensions accurate, is quite time consuming. Some technicians specialise in this type of lathe work, and do out-work for other repair depots. Of course, for a technician doing it daily, it is a lot faster.
For all of the above, for significant sized chips, a lathe is really required to ensure accurate finishing.
5. Acquire a replacement body, and transfer the keys. To correctly fit the keys to a new body can involve a lot of work, costing as much as the replacement body itself. This can be a very expensive option!
After any of the above work has been done, the end of the tenon may be strengthened by capping the end with metal. A metal cap can be bought, but is quite likely a poor fit, say too small in outside diameter, or too large in inside diameter. Or a cap can be custom-turned from stock metal (probably brass - cupronickel in thick rod is not easy to acquire) by a technician with a lathe.
A very successful, and novel approach by myself is to begin with a narrow strip of silver, of appropriate thickness, width and length. Chamfer both ends, and silver-solder them (overlapped) together, to make a ring that is a tight fit on the end of the tenon, stretching slightly larger if necessary. Then using burnishing tools, form the metal over the end of the tenon, and also down to the bottom of the cork groove, incorporating glue if desired. Once again, I am not sure if other technicians carry out this method. Although I have an excellent lathe, I still normally prefer this method. To get it right, and efficient, needs some experience. It takes me about 30 minutes. I often do the other end of the tenon too, when a tenon's diameter is too small.
Post Edited (2004-05-30 14:23)
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