FACTUREE – The Online Manufacturer provides online tools that are permanently free of charge to all interested users. We always look forward to amiable reviews and recommendations, online as well as offline. All tools have been tested, but we assume no liability for the correctness of results.
Roughness depth Rz
To determine the averaged roughness depth Rz, a measuring segment is first established and, in turn, this is divided into (usually five) individual measuring lengths of equal size. The range of the two extreme values in the roughness profile for the respective, individual sections is subsequently divided by the number of measuring sections.
Average roughness value Ra
The arithmetic average roughness value Ra describes the arithmetic average of all deviations in the roughness profile from the median line within the measuring length. The surface roughness established by the calculation is thereby less vulnerable to extreme values than the roughness depth.
A conversion of Rz to Ra and the reverse is not possible as 1:1. However, a conversion interval that contains all possible values can be specified. The rule of thumb that repeatedly emerges for converting Rz = Ra*7 does not go far enough and, based on the extensive scattering of values, can lead to bad surprises in practice.
Roughness class N
Additionally, the surface quality is frequently subdivided into 12 roughness classes or roughness grades. Each roughness class from N1 to N12 has a maximum permissible Ra value according to DIN ISO 1302.
Usage note: A direct allocation of an Rz value to a roughness grade is not possible, due to the conversion interval. In this Rz-Ra calculator the input Rz value is first converted to the average value of the Ra interval and the N class is determined based on this value.