ea contact exists between the teeth of double-enveloping gears while only line contact between those of single-enveloping gears. The worm and worm gear ofa set have the same hand of helix as for crossed helical gears, but the helix angles are usually quite different. The helix angle on the worm is generally quite large, and that on the gear very small. Because of this, it is usual to specify the lead angle on the worm, which is plement of the worm helix angle, and the helix angle on the gear; the two angles are equal for a 90-deg. Shaft angle. When gears are tobe used to transmit motion between intersecting shaft, some of bevel gear is required. Although bevel gear s are usually made for a shaft angle of90 deg. They may be produced for almost any shaft angle. The teeth may be cast, milled,
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