A handbook on the teeth of gears, their curves, properties, and practical construction (1887)
Grant, George B. (George Barnard), 1849-1917 · [Boston] · leaf 77
abs Case III. When the focal distance is infinitely great the curves are parab-olas. One parabola turns about its focus while the other turns about itsopposite focus, but, as the opposite focus is at an infinite distance the sec-ond parabola must move in a straight line at right angles to the line… … Case IV. When the focal distance is finite and negative, the curves arehyperbolas. The opposite focus about which one hyperbola turns is now onthe other side of the curve, which becomes a negative or internal pitch line,as in Fig IV. The link is of finite length and can be practically applied.The…
Gearing
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