Posted by Ian Robinson on May 31, 2002 at 22:46:02:
In Reply to: Re: Swedging Your Rotors posted by js on May 31, 2002 at 13:33:02:
This is a great answer. I do have some things to add. The swedging should also be done to the bearing plate as well as the casing. All swedging needs to be done with the rotor male spindle in the female bearing to get a tight fit without over shrinking the female bearing. Swedging can make an old worn horns valve action smooth and all but silent. This process will help short term but is not going to last long. Depending on how much playing you do it should stay reasonably tight for 6 months to a few years. The nature of the swedging tool tightens the top of the connection only not the full surface area. To do a real fix the rotors should be rebuilt. If your rotors are vented you may want to have them rebuilt to be as tight as possible. The nature of rotors causes them to leak even when the valve is not in use if it is loose or vented. If it is loose and vented this can be a big problem.
Whenever swedging is done the rotors should be dropped to remove up and down play before swedging. Dropping should not be done if this will cause up and down port alignment problems. In this case rebuild is the only way to go.
Tubas that have oversized female bearings on the casing can not be swedged. I have seen some Rudys, Alexes and other older German horns that have this problem. On most of these the bearing plate can still be swedged but the effect is not as good. In this case rebuilding the rotors is the best bet.
Make sure that you have a great repair shop do this type of work. I have seen horns worse (both playing and mechanical) after having major valve work done than before.