OF MATCHING WHEELS, &c.

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Chap. 6.1

applied to communicate motion, instead of bevel gear,where the motion is to be the same, and the angle notmore than 30 or 40 degrees. This joint may be con-structed by a cross, as in the figure, or by four pins, fas-tened at right angles on the circumference of a hoop orsolid ball. It may sometimes serve to communicate themotion, instead of two or three face wheels. The pi-vots, at the end of the cross, play in the ends of the se-micircles. It is best to screw the semicircles to theblades, that they may be taken apart.

article 82.

OF MATCHING WHEELS TO MAKE THE COGS WEAR EVEN.

Great care should be taken in matching or couplingthe wheels of a mill, that their number of cogs not besuch that the same cogs will often meet; because, if twosoft ones meet often, they will both wear away fasterthan the rest, and destroy the regularity of the pitch;whereas, if they are continually changing, they willwear regular, even if they be, at first, a little irregular.

For finding how often wheels will revolve before thesame cogs meet again, take the following

RULE.

1. Divide the cogs in the greater wheel by the cogsin the lesser; and if there be no remainder, the same cogswill meet once every revolution of the great wheel.

2. If there be a remainder, divide the cogs in thelesser wheel by the said remainder; and if it divide themequally, the quotient shows how often the great wheelwill revolve before the same cogs meet.

3. But if it will not divide equally, then the greatwheel will revolve as often as there are cogs in thesmall wheel, and the small wheel as often as there arecogs in the large wheel, before the same cogs meet:

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