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.
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