The essentials of gearing; a text book for students and for self-instruction, containing numerous problems and practical formulas . er will cease to move the follower. This will occur only INTRODUCTION. ZXl when the driving contact point has no com-ponent in the direction of the normal, or lineof action. In this case Bl will coincide withthe tangent at the point of contact, and thedirection of the normal will be through thecenter F. The dotted position of the contactmechanism in Fig. XIII represents this phase,and the normal BF passes through the centerof the follower, since the normal compone
The essentials of gearing; a text book for students and for self-instruction, containing numerous problems and practical formulas . er will cease to move the follower. This will occur only INTRODUCTION. ZXl when the driving contact point has no com-ponent in the direction of the normal, or lineof action. In this case Bl will coincide withthe tangent at the point of contact, and thedirection of the normal will be through thecenter F. The dotted position of the contactmechanism in Fig. XIII represents this phase,and the normal BF passes through the centerof the follower, since the normal component isalways perpendicular to the common tangentof the contact surfaces. Whenever this con-dition occurs, positive driving will cease andthe law may be expressed as follows: Positive rotation can take place only whenthe common normal^ or line of action^ does notjMSSthroiKjh the fixed center of driver, or follower. XV. Pure Rolling. From the considera-tion of Fig. XIV, in Art. XII, it was observedthat there was no sliding action when the tan-gential components were alike in magnitudeand direction. Tliis can take place only when. Fig. XIV. XXU INTRODUCTION the contact is on the line of centers. If such contact is maintained, the result will be purerolling such as exists between two cylinders, or circles. Figures XV, XVI, XVII are examples of pure rolling. Fig. XV illustrates a pair oflogarithmic spirals rotating about centers F and G, with contact at B. The character of thesecurves is such that the angle between the tangent and radius at any point is a constant; thelocus of the points of contact will be FG, and there will be pure rolling with positive rotation,but not a constant angular velocity ratio. As these curves are not closed, they cannot beused to transmit continuous motion. Figure XVI illustrates two elliptical curves revolving about their foci. The contact willalways be on the line of centers FG, and therefore pure rolling will take place. Tlie angularvelocity ratio will
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