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Design of Finke Rotors

by Johannes Finke

We have started to use non metallic valves over 30 years ago and since the beginning we have changed the material and the manufacturing process number of times, always on the search for improvements. The first total "plastic valve" we used was a POM ( polyoxymethylene ) body with a stainless steel shaft in the middle. We experimented several times with a full plastic valve with no metal at all but we realized that the best solution was the combination of stainless steel shaft with a plastic body.

In the very early days my father was actually making valves with a plastic body and a metal mantle around which absolutely did not work out. He continued to use the POM body with the steel shaft for a period of time, the great advantages of this innovation was of course, the reduction of weight on the instrument which was essential for the first triple horns we were building in the early 1970's . The disadvantage of the POM material was a) it was absorbing some water and b) the heat expansion was much more then the one of regular brass material so the horns we built at that time had bigger tolerances ( gap) between casing and rotor. Of course, my father was not satisfied this it so he was studying a lot about plastics and was carefully looking to any new material that came on the market. In the 1980's the Polycarbonate( PC) plastic came on the market and was a great improvement over the previous material. We first used this PC with a 40% glass fiber filler and later with a 60% carbon filler to reduce more and more the heat expansion. This PC material we used had no longer a water absorption and so we were able to reduce the gap between the rotor and the casing ( the greatest problem a player was facing with the POM we used before was when the instrument had not been played for several weeks the rotors had dried out and so the horn could feel not responsive and stuffy. We used the PC plastic for many years ( until the late 1990's and we ( and many players ) were quite happy with it. After I had taken over my father's business a few years ago, I wanted to improve the heat expansion aspect even more and so I visited several trade fairs of the plastic industries. I learned about a new material and decided to try this on our horns, this is the current material , a PPS ( Polyphenylene Sulfide ) plastic which is also used in aircraft industries to replace metal. This has been a wonderful improvement over the previous material. We reduced the expansion the expansion to a bare minimum.

We have used this PPS for the past 5 years and have had very good experience with it. It is acid resistant and it's melting point is at 380 degree Celsius . We heated up instruments in an oven to 80 degree Celsius ( approx.180 F ) and the valves still worked. This material has zero water absorption. As we try to have very tight valves we reduced the gap with the new material to an absolute minimum, the real distance between the rotor and the casing is 0.025 mm with an allowed tolerance of 0.005 mm. As many people perhaps know, we make cylindrical valves instead of the traditional tapered ones. This gives us the possibility of a better control for the tolerances plus interchangeable rotors ( the earlier made instruments can be updated to nowadays used rotors ). In our manufacturing process we do not lap our valves, the surface of the rotors are cut on the lathe and the casings are honed to the final diameter with diamond tools. The material we use does not corrode and does not wear out and if anything happens to the valves, these can be replaced ( including all bearing plates, which are not soldered into the casing), even after many years as the general design of the valve system has not changed. To those customers, who better trust metal valves, we offer regular brass rotors or rotors made completely out of VA steel . These two alternatives, of course, weight a little more. You can put a quality lubrication oil onto the rotors which will not effect the material lifetime at all. It is possible that the action might be a little slower. Using some amount of oil has the positive effect that the "cutting process" of any build-ups is better than with just water lubrication. For any of you who have any further question, please get in contact with me and I will answer you as good as possible.

PHONE: 1 (781) 646-5756

FAX: 1 (781) 646-2480

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