The essentials of gearing; a text book for students and for self-instruction, containing numerous problems and practical formulas . -, but in this case the teeth should be extended slightly beyond thepitch circle in order to protect the last point of contact, which will Ije on the pitch circle. 56. Involute System of Annular Gearing. Fig. 19. The method of drawing the toothoutlines for the involute annular gear does not difter from that of the spur gear. Pitch linesliaving been determined, the base circles are diawn tangent to the line of action, and the invo-lutes of those base circles will b
The essentials of gearing; a text book for students and for self-instruction, containing numerous problems and practical formulas . -, but in this case the teeth should be extended slightly beyond thepitch circle in order to protect the last point of contact, which will Ije on the pitch circle. 56. Involute System of Annular Gearing. Fig. 19. The method of drawing the toothoutlines for the involute annular gear does not difter from that of the spur gear. Pitch linesliaving been determined, the base circles are diawn tangent to the line of action, and the invo-lutes of those base circles will be the required curves. Care must be used in obtaining thelength of the teeth, in order to avoid a second engagement after the full action shall havetaken place. To determine if this interference takes place, it is necessary to construct theepitrochoid of the point of the pinion tooth, or determine the path of least clearance, as inArt. 28, page 15. 44 INVOLUTE SYSTEM OF ANNULAR Fig. 19 illustrates an annular gear of 20 teeth en-gaging a pinion of 10 teeth, the angle of pressurebeing 20°. The pinion driving in the direction indi-cated will establish the first i)oint of contact at A, andthe last point, B, ^^•ill be limited by the height of the tooth, in this case -. The limit of the gear tooth will be determined by the arc drawn from the center ofgear through the point A. Any extension of the in-volute beyond this point will interfere with the pinionflank. The stronger form of the annular gear toothpermits of a greater clearance, which it is advantageousto adopt. If the pinion and gear differ but little in diameter,it is desirable to use the cycloidal system, in which casethe interference may be more easily avoided. It sliouldalso be noted that the advantages to be derived froman increase in the arc of contact and a decrease in theangle of pressure are to be obtained only by the use ofthe latter system. THEORY OF BEVEL GEARING. 45 CHAPTER VI. BEVEL GEARING.
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