Section 10.—CRANK AND ECCENTRIC GEAR.

[168]. Bent crank of round section; retains the fibre and strength of the metal.

[169]. Square forged crank. The crank arm is usually forged solid and the slot cut out by machine.

[170]. Built-up crank. There are other methods of building them. See Mechanical World, December 1885. See also [No. 182].

[171]. Single crank, usually of wrought iron, but often made with cast-iron arm.

[172]. Disc crank. This form is generally adopted when cast iron is employed, and the counterbalance weight cast upon it, to balance the connecting rod, &c.

[173]. Counterbalanced single or double crank.

[174] & [175]. Two forms of crank pin eccentrics; sometimes used to drive the slide valve instead of the ordinary sheave and strap, as [No. 183].

[176]. Crank pin set in a boss formed on the driving wheel.

[177]. Double rod crank.

[178], [179], & [181]. Hand cranks. These should always be fitted with a loose ferrule of wood for the hand if possible, as much power is lost by the slipping of the hand to change its grip as the crank revolves.

[180]. Solid three-throw crank shaft, turned out of a solid forging.

[Larger plate.]

[182]. Built crank. Several modifications of this are in use for large marine shafts.

[183]. Solid sheave eccentric.

[184] & [185]. Split sheave eccentrics.

Large eccentrics cause great loss from friction, unless provided with friction rollers in the sheave; but are sometimes used to avoid an additional crank in shaft.

[186]. Eccentric motion for multiplying travel of eccentric by leverage.

[187]. Crank motion to turn an angle instead of bevil gear and shaft, the cranks being of the form of [Nos. 174] or [175].

[188]. Shifting or variable throw eccentric. The sheave is slotted to fit the shaft, and its throw is governed by a disc having a spiral slot and locking bolt.

[189]. Another form of shifting eccentric. The sliding block is arranged to lock in any part of the slot in the sheave.

[190]. Another form of shifting eccentric, in which the sheave is loose on an eccentric boss cast with the worm wheel, and is revolved by the worm, the bearings of which are fixed to the sheave.

See also [Nos. 606], [712], [720], [728], [729].