What ISO-defined roughness parameter most closely approximates what is measured with replica tape ?
Conceptually, replica tape (with thickness gage) measurements are more like Rz (the ten point average peak-to-valley roughness) than like Ry (the “maximum” peak roughness) because the closing force of the thickness gage slightly compresses the tape and effects an average measurement. In fact, the Rz and Ry parameters are only defined in the context of one-dimensional determinations of roughness using a stylus device. They cannot be directly compared with the two-dimensional measurements (sampling a significantly larger area) obtained with replica tape. (The practical difference between Rz and Ry is, in any case, generally small compared to other sources of error. Besides, the ISO definitions of these parameters has now changed. The “new Rz” is no longer defined in the same way as the old Rz.) Details of all the major definitions governing randomly roughened surfaces tend to be esoteric and a little academic. The most important thing is to cite the measuring method along with any numeri
