When all these parts were assembled, it was necessary to find the centre of gravity of the whole combination, as it is important that it be perfectly balanced.
To find the correct point, a light string was slipped under the horizontal piece and moved back and forth until the vane hung horizontally. The spot where the string touched the wood was marked with a pencil and a 1⁄4-inch hole drilled at this point for the pivot. A corresponding hole was drilled 3 inches deep into the bevelled end of the standard.
A piece of 1⁄4-inch maple dowel was used as a pivot, the upper end being sand-papered until the vane swung freely. The boys found that by placing a metal washer between the vane and its standard, much of the friction was removed. A wire nail driven into the standard through a hole drilled in the horizontal piece would have answered the same purpose as the dowel. When the centre of gravity is not found for the pivot, the vane is apt to tilt forward or backward and not only look badly, but bring considerable friction on one end, so that it will not revolve freely with the wind.
[XVII]
MILLS AND WEATHER VANES
The subject of windmills and weather vanes opened up a field that seemed inexhaustible, and for a while there was a perfect furore of designing and experimenting. As usual, Harry wanted to try great schemes that Ralph knew were impracticable, and it required all his diplomacy to keep the boy down to earth, on something simple and within his power to do successfully.
One of his earliest attempts was a scheme to make a windmill on the principle of a water-wheel, placed horizontally to catch the wind.
Ralph knew that it would not work, but after arguing for some time, he decided to let the youngster learn by experience. While Harry was working at his project, Ralph sketched out and made a vane which he considered an improvement on the first one. It is shown in [Fig. 95]; and it was made without a mill and composed of four pieces. The horizontal piece had an arrow head at the forward end. At the rear end, two pieces of 1⁄4-inch pine were fastened with two small bolts. From the point where they were bolted they curved outward as shown in the top view, and were held in that position by two small strips nailed on with brads, one on the upper and one on the lower side. The centre of gravity was found as before, and the vane pivoted to its standard.