A permanent repair for your broken tenon!
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All woodwind instruments use a system of tenons and sockets to connect their various sections. On wooden and plastic instruments, these tenons can chip, crack, or completely break off the instrument. When this happens, it’s important to repair or replace the tenon.
In most cases, it’s more cost-effective to replace the tenon than to replace the entire section (which requires transferring, re-fitting, and repadding the keys) or the whole instrument.
While some tenons can be successfully repaired without replacing (article, images, and details coming soon!), the tenon pictured here was not salvageable. The owner attempted to glue the broken pieces together, but we learned long ago what the owner learned recently: it’s not possible to glue a broken-off tenon in a permanent way; replacement is what is needed.
Replacing a tenon is pretty basic, provided you have the proper tools…
The first step is to cut off the remaining fragment of the old tenon and bore a socket inside the damaged part. This socket will receive the replacement tenon plug.
Once the hole is cut to the appropriate depth, it’s time to make the replacement tenon plug. Obviously, a wooden instrument will receive a wooden tenon, and a plastic instrument will receive a plastic tenon. These are available pre-made from several of the repair supply houses, but we’ve always made our own. This way, we can ensure that the part fits the instrument exactly. What if the socket was reamed out at some point? What if this is an instrument for which a pre-made part isn’t available? These are some of the reasons we custom make each tenon plug.
The outside tenon plug needs to fit easily, but not too loose, into its corresponding socket, which is one diameter, as well as the hole we cut into the broken part, which is a different diameter and should be a snug fit. Additionally, we need to machine a channel to hold the tenon cork. And at some point, we need to make the overall length of the new tenon match its socket.
The inside diameter needs to have a hole, of course, but some tenons (such as a clarinet bell tenon), need to have an interior taper. So that needs to be accurately machined to match the bore of each section.
Using a lathe for these procedures is absolutely essential to ensure the parts are perfectly round and concentric; otherwise, the new tenon will be off-center, causing the sections to be out of alignment.
Once we’ve completed all of those steps, it’s time to glue and clamp the two parts together. You can clamp the parts on the lathe, but since we’re machining things all the time, we use dedicated clamps for this job. Since we made our tenon plug with a snug fit, we need only a small amount of adhesive, which creates a stronger bond, resulting in a permanent repair.
In some cases, we will need to rebore tone holes that are obstructed by the new tenon plug.
The final step after the parts have bonded is to install and fit the tenon cork and test the instrument.