Re: What the heck is rotor "scooping" ?
Posted: Fri May 27, 2011 8:07 am
You don’t know? With your tech knowledge I tend to suspect a troll. Your tuba may be transparent, but ain’t sure if that goes for your mind, too.
Anyway:
The airpaths are milled out of the massive brass or bronze rotors in most tuba situations. (With some double and triple horns the rotors are hollow. Made of tubing with the airpaths soldered on).
The mass of the massive rotors is problematic in its own right: contributing to the overall weight of the instrument and causing inertia slowing valve speed down.
The airpaths of the rotors ideally are made to line up with the ports in the rotor casings except where the outer wall of the rotor casing acts as part of the acoustical tubing (that is: in direct contact with the buzzed air column).
The passage geometry of the airpath through the rotor valve block is not ideal, as the cross section varies wildly from the circular crosssection of the main tubing. At some places the area of the airpath cross section of a rotor even is smaller than the equivalent area in the adjacent main tubing.
It hardly is possible to scope the airpath of most rotors to approach roundness. That would take rotors with larger diameters. But by scoping out material from the wall between the two airpath chambers and from top and bottom of these chambers, you may approach some degree of evenness in the cross section area all the way through the airpath chamber of a rotor. Tech artistry enters where airpath geometry is optimized without compromising the tech stability and the ability to tolerate normal wear.
Klaus
Anyway:
The airpaths are milled out of the massive brass or bronze rotors in most tuba situations. (With some double and triple horns the rotors are hollow. Made of tubing with the airpaths soldered on).
The mass of the massive rotors is problematic in its own right: contributing to the overall weight of the instrument and causing inertia slowing valve speed down.
The airpaths of the rotors ideally are made to line up with the ports in the rotor casings except where the outer wall of the rotor casing acts as part of the acoustical tubing (that is: in direct contact with the buzzed air column).
The passage geometry of the airpath through the rotor valve block is not ideal, as the cross section varies wildly from the circular crosssection of the main tubing. At some places the area of the airpath cross section of a rotor even is smaller than the equivalent area in the adjacent main tubing.
It hardly is possible to scope the airpath of most rotors to approach roundness. That would take rotors with larger diameters. But by scoping out material from the wall between the two airpath chambers and from top and bottom of these chambers, you may approach some degree of evenness in the cross section area all the way through the airpath chamber of a rotor. Tech artistry enters where airpath geometry is optimized without compromising the tech stability and the ability to tolerate normal wear.
Klaus