Author: clarnibass
Date: 2018-11-04 11:39
>> For the best possible response in the LH F/C action the actuating arm should be as nearly parallel as possible <<
The ideal shape for this linkage is like involute gear teeth, but it's usually unrealistic to change them after the fact and really should be designed and made by the manufacturer to that shape. I think Selmer has made some clarinet with that shape... if I remember...
So making them parallel is the next best option, but because of the soft materials (even relatively firm ones), there is no real precision in the mating surface (even though there is a precision feel), so best to make sure the outer end of the lever side linkage arm is touching (i.e. leaning to that end in the slightly not completely parallel way that it has to be).
>> To achieve this it is sometimes necessary to add a very hard material to the mechanism, I often soldered a very thin brass shim to either the upper or lower surface and then filled the remaining very small gap with thin Teflon (0.005 or 0.010") or even leather (from an old sax pad for instance). <<
Exactly what I sometimes do too. I use silver or nickel-silver but that's just a cosmetic difference.
>> Thanks a lot for replying to me -the surfaces are parallel and the gap between is about 1-1.5 mm. <<
Is that just a very rough guesstimate? That's a huge gap for that linkage. I prefer not to use thicker than 0.5mm material there (meaning the gap has to be no more than that), or even 0.2mm-0.4mm optimally.
On many clarinets that linkage has such a bad shape that it's a bit more of a compromise without doing significantly more work.
>> Remembering those things makes me appreciate even more when I play the R13 <<
I've seen R13s where this linkage was just terrible, basically a sharp angle between the parts, as if it was soldered at an incorrect angle.
More recently Buffet started adding an adjustment screw there, which is a good idea in theory, but it is positioned so the lever arm is so short, increasing travel.
Another issue (common on R13s and many other clarinets) is that the edge of the lever side is relatively sharp. This digs into whatever material you use and squishes it or even tears it. It's worse the thicker the material is. This corner should be rounded, but rounding it too much would increase travel of the lever significantly because of the angle change when pressing it.
>> I used to use leather, but the tech cork is harder, thinner, and wears better. <<
Tech cork isn't really thinner than leather, it is available in many thicknesses, just like leather. I stock tech cork from 0.3mm to about 3.0mm and pad leather is usually not much thicker than the thinnest tech cork.
I often use a synthetic leather material that is similar to leather, about 0.2mm-0.3mm thick, and is tougher than excellent quality pad leather.
If the gap is 1.0mm-1.5mm when the linkage arms are parallel, then first check that the F/C key is opening enough. If not, it is usually stopped by the E/B and/or F#/C# keys and they might need to be opened more. This will move the outer end of the key side closer to the lever side more than the other end, so raising the lever would get it back to parallel and decrease the gap.
If none of that is an issue, I would either solder a shim like Caroline suggested or, if that is not possible for whatever reason (e.g. you want to do it yourself and can't solder) then accept the best compromise instead. Probably using a thicker but much firmer material.
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The Clarinet BBoard
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