Posted by Sean Chisham on December 09, 1998 at 14:21:15:
In Reply to: Horn Operation posted by ...curious on December 09, 1998 at 13:06:49:
This is a fairly common practice. When rotary valves are fit in a tuba, the ports are lined up properly in both the open and closed position, then the spindle on the underside is scored in order to make this procedure easier for the sizing of new cork bumpers.
In piston instruments, the felts and corks are good deal larger and spread out the forces thus usually lasting a bit longer. When it comes time to replace them one usually purchases pre-sized to fit your pistons. Pistons don't usually require alignment, in my experience due to the availability of parts.
If you have a rotary instrument with misaligned ports then it may be time for new cork.
sean