Cast aluminum and wood (painted) on a vertical panel.
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The miter gears are the two models on the right. Miter gears are used to transmit motion between two shafts placed at right angles to each other. Since the gears are of equal diameter, they both revolve at the same speed. The angle of the grooves to the shaft is 45° in all miter gears. Helical miters are so cut that they are noiseless. Therefore they are used for high speed transmission.
[Virginia Downward & William M. Clark, 1930]
[Editor’s Note: Lower model missing in the Boston models. The lower model on the left shows the action of bevel gears. Bevel gears also run at right angles to each other but the two gears in combination are of different sizes. Since the speed transmitted is different these gears are used when a differential speed is desired. The angle of the teeth depends on the diameter on the two gears. The spiral gears are developed primarily for automobile drives but are applicable to any high speed machinery where quiet running is desired. Bevel and helical gears can be seen in the Illinois Gear Collection at Cornell (KMODDL) or on the Ohio State University online gear museum. FCM]