Gear 1 to be tested is mounted with segment 2 on fixed axis B. Roller a and contact point b of carriage 3 lie on straight line N-N, parallel to the motion of the carriage. The distance to roller a from axis A equals the radius of the base circle of gear 1 . When gear 1 is turned, the rolling motion of segment 2 is transmitted by flexible steel bands 4 to lever 5 which is deviated about fixed axis A so that S/K=r/R. • Under this condition, points of tangent N-N describe an involute of a circle of radius r. If there is no error in the tooth profile of gear 1, contact point b remains stationary with respect to moving carriage 3. Errors in tooth profile from that of a true involute deviate contact point b whose motion is transmitted to indicator c.
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