GB630243A - Linkage for the generation of involute-like curves - Google Patents

Abstract

630,243. Gauging gear teeth. WIGAN, E. R. Dec. 29, 1947, No. 34551. [Class 106 (ii)] [Also in Group XX] A linkage for checking a curve approximating to an involute curve for a spur-gear tooth comprises an arm 4, Fig. 2, pivoted on a support 1 located over the centre of the involute base circle, a second arm 6 coupled to the arm 4 by a pivot 5 and carrying a tracing point 8, and a guide piece 7 pivoted in a bracket 18 and adapted to receive the second arm 6. The pivot 5 is adjusted relative to a scale on the arm 4 to lie at a distance approximately 0.8 times the radius of the base circle from its centre and on rotation of the arm 4 about the centre of the base circle with the centre of the guide-piece 7 over the origin T the point 8 traces a curve approximating to an involute. The end of the arm 4 may be integral with a plate 1 having cross wires 3 by means of which the pivot of the arm 4 may be accurately located over the centre of the base circle. In a modification, Figs. 3, the arm 6 is replaced by a triangular member P<SP>1</SP>, S<SP>1</SP>, T<SP>1</SP> having a rightangle at S<SP>1</SP>, the guide-piece 7 being located at S some 10 to 20 degrees away from the tooth origin T. The tracing point T<SP>1</SP> is thereby offset from the axis of the arm 6. In a further modification the guide-piece 7 instead of being located exactly above the tooth-origin T is mounted eccentrically in a frame which is free to pivot about another point slightly to the right of T. The approximation of the curve to an involute may be varied by the adjustment of the position of the pivot 5 along the arm 4.