Machine drawing; a practical guide to the standard methods of graphical representation of machines, including complete detail drawings of a duplex pump and of a direct-current generator . MACHINE DRAWING 137 shown dotted, by rolling on the inside of the pitch circle of the gearB, generates the hypocycloid PE, which forms the flanks of the teethon gear B; and by rolling on the outside of pitch circle of gear A,generates the epicycloid PF, which forms the faces of the teeth ongear A. In like manner the circle whose center is D, by rolling onthe inside of the pitch circle of gear A, generates the
Machine drawing; a practical guide to the standard methods of graphical representation of machines, including complete detail drawings of a duplex pump and of a direct-current generator . MACHINE DRAWING 137 shown dotted, by rolling on the inside of the pitch circle of the gearB, generates the hypocycloid PE, which forms the flanks of the teethon gear B; and by rolling on the outside of pitch circle of gear A,generates the epicycloid PF, which forms the faces of the teeth ongear A. In like manner the circle whose center is D, by rolling onthe inside of the pitch circle of gear A, generates the hypocycloidPG, which forms the flanks of the teeth on A; and by rolling on theoutside of the pitch circle of B, generates the epicycloid PH, whichforms the faces of the teeth on B. The circles C and D are calledthe describing circles. If the gear B is the driver and is turning in. Fig. 114. Construction of Eplcycloidal Gears the direction shown by the arrow, the flanks of its teeth act on thefaces of the teeth on A from the point where they first come incontact until the point of contact reaches the pitch point; and fromthe pitch point on until the contact ceases, the faces of the teeth onB act on the flanks of the teeth on A. In other words, the hypo-cycloidal part of the tooth curve on one gear is generated by thesame describing circle that generates the epicycloidal part of thetooth on the other gear with which it is in contact. This mustalways hold true, in order to have the gears run properly. The arcIP of the describing circle C, together with the arc JP of the describ-ing circle 2), forms what is called the path of contact; that is, thepoint of contact between the teeth is always somewhere on the 138 MACHINE DRAWING line IP J. If the gear A were the driver, the direction of rotationremaining the same, the path of contact would be LPK. To design a pair of
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