Comparison of different methods for computing the two-dimensional envelope for surface finish measurements

In the envelope system of surface finish measurement, an envelope traced by a circle of definite radius gives the reference line for a two-dimensional surface profile. Geometrical construction of this envelope, on actual surface profiles, is fairly easy. For evaluating the benefits of the E-system it is advantageous to use digitized surface profiles, to compute the envelope from the profile ordinates. There are several ways of computing the envelope from digitized surface profiles and this paper explains the various methods and gives the times taken for computation. © 1976.