Synopsis
This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1900 Excerpt: ...to the worm will rotate the worm-wheel a distance Fig. Bis. equal to its pitch; consequently, if there are 40 teeth in the worm-wheel, a single-threaded worm will have to make 40 revolutions in order to turn the wheel once. /'. II.--26 1872. In Fig. 617 is shown a section of a rack and pinion, both having epicycloidal teeth. The arc C C represents part of the pitch circle; it is on the pitch circle that all the teeth are laid out. The diameter of a gear or wormwheel is always taken as the diameter of this circle, unless otherwise specially stated as "diameter over all," or "diameter at tTie root," etc. The pitch of the teeth of the gear-wheel is the distance from the edge of one tooth to the corresponding edge of the following tooth measured on the pitch circle; it is mai ked pitch Fl-G16-in the figure. The length of the tooth of a gear-wheel is.7 of its pitch,.4 of it, called the root, being below tr within the pitch circle, and.3 of it, called the addendum, being above or without the pitch circle. Thus, if the pitch of the teeth of a gear-wheel is 2 inches, the length of the teeth below the pitch circle is 2x.4 =.8 of an inch; and the length of the teeth above the pitch circle is 2 X.3 =.6 of an inch. Consequently, we have only to multiply the pitch by.4 to obtain the length of the teeth below the pitch circle, and by.3 to obtain the length of the teeth above the pitch circle. The thickness of the teeth of a cast gear-wheel equals.48 X P, that is,.48 of the pitch; therefore, the thickness of the above teeth is.48 X 2, or.96 of an inch. A rack may be considered as a gear-wheel rolled out so as to make the pitch circle a straight line, as C' C". The teeth of racks are proportioned by the same rules as those of gear-wheels. 1873. For...
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