The Boiler.--In the centre of the boiler make a dent, to act as bottom
bearing for the spindle. From this centre describe a circle of 5/8-inch
radius. On this circle must be made the steam port or ports. Two ports, at
opposite ends of a diameter, give better results than a single port, as
equalizing the pressure on the vanes, so that the spindle is relieved of
bending strains. Their combined area must not, however, exceed that of the
single port, if one only be used. It is important to keep in mind that for
a turbine of this kind velocity of steam is everything, and that nothing is
gained by increasing the number or size of ports if it causes a fall in the
boiler pressure.
The holes are best made with a tiny Morse twist drill. As the metal is
thin, drill squarely, so that the steam shall emerge vertically.
For the upper bearing bend a piece of tin into the shape shown in Fig. 67.
The vertical parts should be as nearly as possible of the same length as
the spindle. In the centre of the underside of the standard make a deep
dent, supporting the metal on hard wood or lead, so that it shall not be
pierced.
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