A rolling blog of everyday life on and around the workbench (Archived - September 2017)

01/09/2017: Had a Selmer Reference 54 tenor come in for some work recently, and as part of my 'tweakery' package I upgraded the low C/Eb rod screw.
I've mentioned this curious feature before, in my review of the Ref. 54 alto, and noted that there are a number of things that are less than ideal about it - so I figured it'd make an interesting article to discuss it in more detail and have a look at the process of replacing it.

There are a number of ways the low C/Eb keys can be mounted on a horn. On vintage horns you're more likely to find that both keys are mounted on a single shaft - a plain old rod screw. On even older horns you might find that the keys are mounted individually on their own rods screws - but the modern trend is to mount the keys individually on point screws.
This last method makes the most sense; these two keys often get knocked, and it's far easier to deal with a bent key that's mounted on point screws than one that's mounted on a (now bent) rod. It's also a lot easier to deal with wear and tear on point screw mounted keys - and while I wouldn't say that these two keys wear any faster than any of the other keys, the effects of it seem to have more of an impact. Even a slight bit of free play on the low C key can throw up a leak...and this'll have a noticeable impact on the stability of your subtone bell notes.

A few years ago Selmer came up with the idea of using sprung inserts in the point screw key barrels, the idea being that the insert (a tube with a spring on one end) would sit in the key barrel and exert a constant force against the point screws that are holding the key in place.
It's a nifty idea on paper, but in practice I find it leaves the action feeling slightly 'approximate' - because there's always a degree of end play in the system due to the action of the springs. Contrast this with standard point screws, where (ideally) the key is held snugly in place - not so tightly that the normal up and down action of the key is hindered, but tight enough to ensure the key cannot move in any other plane.
You could argue that point screw keys are prone to wear, and that once they do so they'll wobble about - and that the sprung system takes care of this wear automatically. And this is true - but it does so at the expense of precision...which means you never have a truly tight action, nor the sense of feel that comes with it.
Swings and roundabouts, as ever.

But then they went a step further and incorporated a spring in a rod screw - and I really can't see why on earth they did it.
Here's the rod screw in question, alongside the low C key. It's essentially the same system - the split pivot rod is mounted on a pair of point screws and has a spring in the middle to provide a constant force against the screws.
There are a couple of potential issues that trouble me about this design - the first of which is that by splitting the rod in two and fitting a spring in the middle, you reduce the stiffness of the rod. These are large keys, and the low C in particular tends to suffer with quite a bit of flex in use (which is why many horns feature double key cup arms on this key). What this means is that an otherwise perfectly set pad can be made to leak by virtue of the player being a bit heavy-handed. The harder you press the key, the more the metal tries to flex - and this typically results in a portion of the pad lifting away from the tonehole. You could say "Then don't press so hard!" - but when the going gets hard and fast we all have a natural tendency to press harder. It's just one of those things. So anything that can be done to increase the stiffness of the keys is a welcome addition - and anything that reduces it...well, not so much.

The second issue is perhaps slightly more off the wall.
Take a look at the rod screw - notice that it's not straight. This is its 'resting state'. When you fit it to the horn, it gets worse.
You can see that the bend is now rather more pronounced because the spring is under compression. With a bit of very careful jiggling you can get the screw to sit straight - you just have to find the point where the force is in balance. It's like that old trick of squeezing a coiled spring between your fingers without it flying off across the room.
When the keys are fitted they hold the rod in equilibrium - but it's not a particularly stable state, and it rather depends on the integrity of the spring. If it's got a bend or a kink in it, the rod will never sit straight. This means there's a sideways force acting on the key barrels, and when you couple that with the motion of the keys you end up with friction...and friction means wear, eventually. In some cases you might even notice a grating sound as the keys are pressed - which means that one of the rods is rotating, or the spring has bulged and is rubbing against the key barrel.

I think sprung pivots are a questionable-enough feature on the point screws, and a completely silly one on the low C/Eb - and my standard tweak is to replace the rod with a solid one. This adds stiffness to the mechanism and does away with the potential for friction from an off-centre rod screw.
And it's a simple upgrade - all that's needed is a length of rod of the right diameter with holes in each end to accommodate the point screws.

There are a few things to consider, though. The point screws are bullet-headed, which means that only the tip of the point is tapered - the remainder of the screw is cylindrical...which means the hole in the rod has to be drilled very precisely (or the rod will wobble). You also don't want to drill the hole out too deep, otherwise the tip of the screw will be floating in air and won't have any scope for future adjustment.
One way around this is to drill a stepped hole - a smaller pilot hole to accommodate the tapered tip, and a larger one to take the main shaft. This'll work fine, but it's a lot of fiddling about and will require some very accurate drilling. A better bet is to use a profiled reamer that will cut a hole that perfectly matches the size and shape of the tip.
These are easy enough to make; a length of silver steel turned to size, profiled to match the shape of the screw tip and then heat treated to harden and temper the tool (so that it doesn't wear out halfway through the job). It takes as much time to make such a tool as it does to faff about precision-drilling a pair of stepped holes...and once you're done, the tool can go into a drawer ready for the next time.

It might all sound like Nth-degree mechanical twiddlery, but the upgrade makes a noticeable improvement to the performance of the lower notes. They're far more stable and centred - and much more consistent over a wider range of playing styles.
And the very best of it is that it's a completely reversible mod. If you don't like the results, you simple pop the new rod screw out and refit the old one.
I always put the old ones into a sealed bag and throw them in the accessory compartment of the case, where - as far as I've seen - they remain for all time.