[Illustration: FIG. 67.--Simple steam turbine.]
For the turbine wheel take a piece of thin sheet iron or brass; flatten it
out, and make a slight dent in it an inch from the two nearest edges. With
this dent as centre are scribed two circles, of 3/4 and 1/2 inch radius
respectively. 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.
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