Mill Gearing

Under this head we purpose to treat of the best formation of the teeth of wheels, of the connection of shafts, termed couplings, of the disengaging and reengaging of the moving parts, and of the equalization of motion ; and to them we shall annex some further observations upon the general construction of Machinery. To avoid unnecessary repetition, we shall, previously to entering upon the formation of the teeth of wheels, give a general definition of the terms most commonly in use.

Cog-wheel is the general name of any wheel which has a number of teeth or cogs placed round its circumference.

Pinion is a small cog-wheel that has not in general more than twelve teeth; though, when two-toothed wheels act upon one another, the smallest is not unfrequently distinguished by this term ; as is also the trundle, lantern, or wallower, when talking of the action of two wheels.

Trundle, lantern, or wallower, is sometimes used in lieu of a pinion. It is represented at fig. 36.

When the teeth of a wheel are made of the same material, and formed of one piece with the body of the wheel, they are called teeth; when of wood, or some other material, and

affixed to the outer rim of the wheel, cogs; in a pinion they are called leaves ; in a trundle staves.

When speaking of the action of wheel-work in general, the wheel which acts as a mover is called the leader, and the one upon which it acts the follower.

If a wheel and pinion are to be so constructed that the one shall give, and the other receive, impulse, so that the pinion shall perform four revolutions in the time that the wheel is performing one, they must be represented by two circles, which are in proportion to each other as four is to one. When these two circles are so placed that their outer rims shall touch each other, a line drawn from the centre of the one to the centre of the other is termed the line of centres; and the radii of the two circles the proportional radii. These circles are sometimes called proportional circles, but by mill-wrights in general pitch lines.

The teeth which are to communicate motion must be formed upon these two circles. The distance from the centres of two circles to the extremities of their respective teeth, is called the real radii ; and, in practice, the distance between the centres of two contiguous teeth, that is, the distance from the centres of two teeth measured upon their pitch line, is called the pitch of the wheel. The straight part of a tooth which receives the impulse is called the flank, and the curved part that imparts the impulse, the face.

Two wheels acting upon one another in the same plane, having their axes parallel to each other, are called spur gear; when their axes are at right, or other angles, bevelled gear.

Continue>> On the Teeth of Wheels