Chap, 5.2 The fundamental law of gearing( 5) 2. The involute tooth form The line(string) is always tangent to the basic circle 2. The center of curvature of the involute is always at the point of tangency of the string with 发生线 the cvlinder 3. A tangency to the involute is 渐开线 then always normal to the involute string. the length of which is the instantaneous radius of curvature of the involute curve KB= AB base circle 4. There is no involute curve within the base circle2. The Involute Tooth Form involute base circle 1. The line(string) is always tangent to the basic circle. 4. There is no involute curve within the base circle. Chap.5.2 The fundamental law of gearing(5) 2. The center of curvature of the involute is always at the point of tangency of the string with the cylinder. 3. A tangency to the involute is then always normal to the string, the length of which is the instantaneous radius of curvature of the involute curve