ly. Then scratch a series of radial marks between the circles, a
fifth of an inch apart. Cut out along the outer circle, and with your
shears follow the radial lines to the inner circle. The edge is thus
separated into vanes (Fig. 68), the ends of which must then be twisted
round through half a right angle, with the aid of a pair of narrow-nosed
pliers, care being taken to turn them all in the same direction.

[Illustration: FIG. 68.--Wheel for steam turbine, showing one vane
twisted into final position.]

A spindle is made out of a large pin, beheaded, the rough end of which must
be ground or filed to a sharp point. Next, just break through the metal of
the disc at the centre with a sharpened wire nail, and push the spindle
through till it projects a quarter of an inch or so. Soldering the disc to
the spindle is most easily effected with a blowpipe or small blow-lamp.

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. If this accident occurs the piece is useless.

Place the wheel in position, the longer part of the spindle upwards, and
move the standard about until the spindle is vertical in all directions.
Scratch round the feet of the standard to mark their exact position, and
solder the standard to the boiler. The top of the standard must now be bent
slightly upwards or downwards until the spindle is held securely without
being pinched.

A 3/16-inch brass nut