Various forms of friction gearing are much used, the chief objection to
this kind of gear being the excess of pressure on the bearings required
to give sufficient grip to drive the gear.
=664. The common form of flat-faced friction gear= for hoisting
purposes, &c. See No. 1211. The required pressure is given by a weighted
lever.
=665. Friction bevils,= plain faces, for governor driving, &c.
=666. Friction bevils,= the pinion being usually of hard leather; the
pressure may be applied in the direction of either of the arrows.
=667. Multiple ~V~ gear.= A common mistake is to run these too deep in
gear; the narrower the surfaces in contact, short of the seizing or
crushing point, the less the power wasted in friction.
=668. A very small pinion of leather, wood, or rubber= is frequently
driven by a large driving wheel for obtaining high speed with
steadiness, for driving dynamos, fans, &c.
=669. Disc wheel and rubber pinion,= arranged to reverse motion or vary
speed. See No. 1595. The motion is reversed by throwing either wheel
into gear with the pinion, and the speed varied at will by raising or
lowering the pinion, used for screw presses.
=670. Wedge friction gear.=
[Illustration: 650.-670.]
=671. Coupled bearings= for friction gear, to allow of any required
pressure or “bite,” the strains being self-contained.
See also No. 737, 738, 1294.