s, as in the preceding instance, made up of flat brass
plates and a ring of tubing, and the bearings, BG1, BG2, of brass tube. But
the wheel is built up of a disc 3 inches in diameter, round the
circumference of which are 32 equally-spaced buckets, blades, or vanes,
projecting 5/8 inch beyond the edge of the disc. The wheel as a whole is
mounted on a spindle 3-1/8 inches long, to which it is secured by three
nuts, N1 N2 N3. One end of the spindle is fined down to take a small
pinion, P1, meshing with a large pinion, P2, the latter running in
bearings, BG3, in the wheel-case and cover. The drive of the turbine is
transmitted either direct from the axle of P2 or from a pulley mounted on
it.

CONSTRUCTION.

[Illustration: FIG. 71.--Plate marked out for turbine wheel blades. B is
blade as it appears before being curved.]

The Wheel.--If you do not possess a lathe, the preparation of the spindle
and mounting the wheel disc on it should be entrusted to a mechanic. Its
diameter at the bearings should be 5/32 inch or thereabouts. (Get the
tubing for the bearings and for the spindle turned to fit.) The larger
portion is about twice as thick as the smaller, to allow room for the screw
threads. The right-hand end is turned down quite small for the pinion,
which should be of driving fit.

The Blades.--Mark out a piece of sheet iron as shown in Fig. 71 to form
32 rectangles, 1 by l/2 inch. The metal is divided along the lines aaaa,
bbbb, and ab, ab, ab, ab, etc. The piece for each blade then has a central
slot 5/16 inch long and as wide as the wheel disc cut very carefully in it.

Bending the Blades.--In the edge of a piece of hard wood 1 inch thick
file a notch 3/8 inch wide and 1/8 inch deep with a 1/2-inch circular
file, and procure a metal bar which fits the groove loosely. Each blade is
laid in turn over the groove, and the bar is applied lengthwise on it and
driven down with a mallet, to give the blade the curvature of the groove.
When all the blades have been made and shaped, draw 16 diameters through
the centre of the wheel disc, and at the 32 ends make nicks 1/16 inch deep
in the circumference.

True up the long edges of the blades with a file, and bring them off to a
sharp edge, removing the metal from the convex side.

Fixing the Blades.--Select a piece of wood as thick as half the width of
a finished blade, less half the thickness of the wheel disc. Cut out a
circle of this wood 2 inches in diameter, and bore a