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8 How Brass Instruments Are Made
major acoustical significance, although some manufacturers restore a circular crosssection by forcing steel balls through bent tubing.
In any process which involves changing the shape of metal, the workpiece
becomes harder. In both hand craft and factory methods, the brass has to be annealed
after each step to restore its softness and ductility. Annealing is the process of
heating metal until it is red hot and then quenching in water. This changes the
crystalline structure of metal which has been hardened by hammering, burnishing or
bending and leaves it soft and malleable for further operations. One of the decisions
a manufacturer has to make is whether to leave brass instrument bells finally workhardened or annealed.
In some factories, small sections of tubing are formed from sheet metal by ‘deep
drawing’ in presses: the brass sheet is placed between two steel dies and forced into
the shape of a saucer; subsequent pairs of dies press the brass via a cup shape into a
section of tube of the desired shape which is then cut to length at both ends. Sections
of standard tube or deep-drawn pieces can be placed between external steel dies and
expanded by hydraulic pressure to the required size and shape. These industrial
techniques are expensive to tool up, but they allow large numbers of components to
be produced very economically.
8.4 Valves
There is now little difference in performance between piston and rotary valves, and
the use of one rather than the other is largely a matter of tradition. With a piston
valve, the length of travel has to be at least one bore diameter. Because with rotary
valves there is of necessity some system of levers to transform the linear motion of
the touchpiece into a rotation of the rotor, the connectors can be designed so that the
length of travel of the touchpiece is arbitrarily small. In practice, however, the travel
of the player’s finger and the restoring force of the spring are not greatly different
for rotary and piston valves. The biggest distinction is that when a rotor is halfway
between its two positions, the windway is almost blocked, whereas when a piston
is half depressed, air can pass through both the direct passage and the valve loop,
albeit with some constriction. With sufficient lip control, a player can ‘half-valve’ a
piston instrument to produce a glissando between notes.
The most common purpose of the valve is to extend the tube length, lowering
each of the series of notes available to the player by a semitone, two semitones or
a larger interval, depending on the relationship between the air column lengths with
and without the valve operated. By far the most widely used arrangement is for
the valve operated by the first finger to give a pitch lowering of two semitones, the
second finger to lower by one semitone and the third finger to give three semitones.
The right hand is used for these three valves except with the french horn, where
the right hand has maintained its position in the bell for hand-stopping and the
left hand operates the valves. There have been, however, a significant number of
instruments in Germany which have the role of the first and second fingers reversed
8 How Brass Instruments Are Made
major acoustical significance, although some manufacturers restore a circular crosssection by forcing steel balls through bent tubing.
In any process which involves changing the shape of metal, the workpiece
becomes harder. In both hand craft and factory methods, the brass has to be annealed
after each step to restore its softness and ductility. Annealing is the process of
heating metal until it is red hot and then quenching in water. This changes the
crystalline structure of metal which has been hardened by hammering, burnishing or
bending and leaves it soft and malleable for further operations. One of the decisions
a manufacturer has to make is whether to leave brass instrument bells finally workhardened or annealed.
In some factories, small sections of tubing are formed from sheet metal by ‘deep
drawing’ in presses: the brass sheet is placed between two steel dies and forced into
the shape of a saucer; subsequent pairs of dies press the brass via a cup shape into a
section of tube of the desired shape which is then cut to length at both ends. Sections
of standard tube or deep-drawn pieces can be placed between external steel dies and
expanded by hydraulic pressure to the required size and shape. These industrial
techniques are expensive to tool up, but they allow large numbers of components to
be produced very economically.
8.4 Valves
There is now little difference in performance between piston and rotary valves, and
the use of one rather than the other is largely a matter of tradition. With a piston
valve, the length of travel has to be at least one bore diameter. Because with rotary
valves there is of necessity some system of levers to transform the linear motion of
the touchpiece into a rotation of the rotor, the connectors can be designed so that the
length of travel of the touchpiece is arbitrarily small. In practice, however, the travel
of the player’s finger and the restoring force of the spring are not greatly different
for rotary and piston valves. The biggest distinction is that when a rotor is halfway
between its two positions, the windway is almost blocked, whereas when a piston
is half depressed, air can pass through both the direct passage and the valve loop,
albeit with some constriction. With sufficient lip control, a player can ‘half-valve’ a
piston instrument to produce a glissando between notes.
The most common purpose of the valve is to extend the tube length, lowering
each of the series of notes available to the player by a semitone, two semitones or
a larger interval, depending on the relationship between the air column lengths with
and without the valve operated. By far the most widely used arrangement is for
the valve operated by the first finger to give a pitch lowering of two semitones, the
second finger to lower by one semitone and the third finger to give three semitones.
The right hand is used for these three valves except with the french horn, where
the right hand has maintained its position in the bell for hand-stopping and the
left hand operates the valves. There have been, however, a significant number of
instruments in Germany which have the role of the first and second fingers reversed