In cases where surface roughness needs to be measured with great precision, elaborate instruments must be used. These are expensive, and often unsuitable for workshop use, where roughness of machined surfaces can usually be assessed conveniently and with sufficient reliability using visual and tactile (fingernail) comparison with a standard set of surfaces machined in the same way.
Rubert's range of Roughness Comparison Specimens can help in such cases. They are simple to use, inexpensive, and hence widely used in many different applications. The golden rule to follow, is to use comparison specimens which have been machined by the same process as the workpiece being checked.
This set consists of 30 comparison specimens, covering six of the most commonly-used machining methods: 6 cylindrically turned, 6 end-milled, 6 horizontally milled, 6 surface-ground, 3 lapped, 3 reamed/drilled.
The label states the Ra values of each specimen in both metric and imperial units. (Rz-value label available on request).