Posted on January 2, 2014
Understanding Saxophone Key Fitting: Hinge Tube and Post Facing
A large part of the mechanical rebuild service I provide is invisible to the end user. The result of the job can easily be felt by the player, but the actual mechanical work that is done is literally out of sight, though key fit has repercussions for the adjustment materials that can be used, the pads that can be used, the seal of the the pads, and more- and it is the type of work that can only be done during a full overhaul. For a little primer on why key fit can have such far reaching effects, watch this video here.
I describe the work this way on my Saxophone Repairs page:
–MECHANICAL RECONSTRUCTION OF THE KEYWORK
a restoration of the keywork to better-than-new mechanical condition. When this work is completed, your keywork is as smooth and as silent as it can possibly be, and the mechanism is working so perfectly even Adolphe Sax would approve. ALL play is removed from the hinge tubes and pivot rods. Hinge tubes are gently swedged tight using collets, with regard to the integrity of the finish, and then made square and true with hinge tube facers so that the bearing surfaces of the ends of the hinge tubes are perfectly flat, thus ensuring a long-lasting and smooth fit. All posts are faced flat and swedged tight around the rod. The pivot screw bearing surfaces are checked and if the screw is uneven, it is replaced with an original replacement part. The pivot receivers on the pivot rods are thoroughly cleaned out, checked, and perfected to match the pivot screw exactly. Then the pivot screw post is counterbored until the pivot screw and pivot rod fit perfectly, being absolutely free with no play. This can only be done if the related pads and adjustment materials are being replaced, and should be done in conjunction with a chemical cleaning, tonehole leveling, and pad/felt/cork/teflon replacement. This is the service to get if you want your horn to be as perfect as I can possibly make it and better than it was when it left the factory. This work is priced, discussed, and decided upon ONLY by having the instrument in-hand.
What I want to show you today is what the end of a hinge tube (a key that has a long rod running through it) looks like before, during, and once the process is completed. This should give you some idea of why wear occurs in the first place, as well as why the way I do mechanical work can last for many decades if properly taken care of.
Swedging is the process that squeezes the hinge tube down around the rod. This snugs the key around the rod, and also lengthens the key a little bit, recreating (or in many cases, creating for the first time) a snug fit of the key between the posts, the goal of which is to completely restrict movement in every direction EXCEPT the direction the key is supposed to go- up and down- which must be as close to frictionless as physics will allow.
Hinge tube shortening/facing tools make the faces of your hinge tubes square and flat. It is a precision job, and there is no way around it other than losing precision as well as the longevity of the job. It is an unfortunate fact that hinge tube shorteners/facers are not used in repair shops as much as they should be- from my experience on the bench (though keep in mind I don’t often see people who are perfectly happy with their current repairman) it seems typical to leave that part of the job out entirely, which results in a very short-term fix as the ends of the hinge tubes are uneven and quickly wear down high spots, resulting in keys that are no longer well fit.
Facing the hinge tubes and the posts means you must swedge the key longer than you would otherwise, since you are removing material by the facing process. For this reason, achieving truly perfect key fit by swedging and facing takes quite a bit longer than just swedging alone.
The photos below are of an original finish, undamaged, good physical condition Selmer Mark VI.
Before swedging hinge tube ends. Again, this is undamaged, original finish and a high-quality saxophone- this is very close to how it looked from the factory. Not exactly a super smooth bearing surface, eh? Also if you’ve got repairman eyes, you may even be able to tell its a little ovaled out, which was causing the rod to rock around inside the key.
After swedging, and the key is now tight around the rod, but the hinge tube has not been faced yet. I used a collet swedger on this one like usual on hinge tube ends, which I feel much more evenly shrinks the tube down around the rod than pliers type. In this photo, you can also see a tiny bit of lapping compound used to make the rod turn freely in the key after swedging that my naptha + pipe cleaners didn’t clean off as well. When I saw this photo, I started not only using pipe cleaners to clean out the interior but I also wipe the hinge tube end off before facing.
Halfway through hinge tube facing. See how the outer edge was so much higher than the interior?
Hinge tube faced. The key is tight around the rod and the hinge tube ends are faced flat and square and smooth. Fit snug between well aligned and faced posts and you’ve got a recipe for multi-decade key fitting jobs.
A post (on a different horn) that has been faced flat. This is a threaded post. On through-posts, like those in your upper and lower stacks, it is important to first tighten the post around the rod (usually rods are a little loose inside the post. Here is a catastrophically bad example that would have required a post bushing) and then face it flat.
A photo showing the hinge tube shortening/facing tool in action on a key from a Martin Committee III aka “The Martin” tenor. The facing tool is kept perfectly aligned by an exact size pilot that fits into the hinge tube and threads into the facing tool.
A photo showing the facing tool being applied to a post. In this photo, you can see the pilot of the facing tool going coming out the other size of the post.
So, there you have a visual tour of a portion of the invisible but very tangible work of key fitting. I hope you found it illuminating! A saxophone key that is fit tight around its rod, tight between its posts, with posts that are tight around the rod, posts that are aligned perfectly with each other, and flat facings on the hinge tubes and the posts will lead to a very, very long lasting key fit, and key fit is one of the most important portions and an overhaul that makes great pad work possible.