Tone Hole Replacement

When an oboe develops a crack through tone holes, it is very difficult to keep the pertinent pads sealing. Even when pinned, the wood will swell and shrink a bit with the weather, and the crack may leak right at the pad seat. The best remedy for this is to install a plastic bushing, preferably threaded, so that it can’t possibly come loose later. This bushing should also be installed deeply, to get below the depth of the crack, if possible. This makes it less likely that the crack can leak around the tone hole later, should the wood pull away from the epoxy as the wood responds to climactic changes.

I make my own tone hole inserts on a small precision lathe, to suit the size of hole needing replacement. This requires a fair amount of machining knowledge, but the information is readily available in libraries, or on the internet.

Tone Hole Insert

The next step is to securely, and accurately arrange the oboe on a drill press, or milling machine in this case. In the picture is a jig I purchased from one of the woodwind tool suppliers, with the oboe securely clamped

After the oboe is on the machine, I need to be assured that the tone hole will be level with the drill bit to be used. I do this by using a steel rod, machined flat on the bottom. I touch it against the tone hole and check for level with cigarette paper, just like checking a pad. I adjust the oboe radially as necessary.

Once the oboe is level in the machine, I need to guarantee that I will be drilling exactly centered over the cracked tone hole. I use a center finder, which is a steel rod, pointed at one end, to fit into any tone hole, and cylindrical at the other end, to fit into the drill chuck. It is actually in two parts, and held together with a spring. When the hole is not centered under the drill chuck, the center finder is offset. When the tone hole is perfectly centered, the center finder looks like one continuous steel rod. There are handwheels on the milling machine which move the table, to precisely locate the tone hole.

When I am confident the oboe is secure and centered, I can begin drilling the tone hole. I use the homemade drill on the left to drill a two step hole about 4 to 5 mm deep. Then I use the tap to cut screw threads in the wood, in the smaller, deeper section of the drilled out hole. After threading the insert in with 5 minute epoxy, I cut the top bevel of the insert with a modified drill bit, which I ground on a standard bench grinder. The last touch is to add a very small inside bevel with the tool on the right. The tone hole insert in the picture actually belongs to a larger set of cutters. I was afraid a smaller one might not show enough detail in the photo.