Surfaces and their Measurements
This book is primarily intended to help designers and inspectors to understand the fundamentals of surface metrology and, where appropriate, point to relevant procedures for specification.
TABLE OF CONTENTS Surfaces and their Measurements
Chapter 3: Profile and Areal (3D) Parameter Characterization
3.1 Specification
Before embarking upon the parameter evaluation, some terms have to be established:
| R | is roughness profile, |
| W | is waviness profile, |
| P | is primary profile obtained from the transducer, which incorporates the R and W. |
These are defined in Section 2.1.
To specify a value, three characteristics should be incorporated. Thus, T.n.N represents the notation:
| T | is the type of profile e.g. R, |
| n | is the parameter suffix e.g. q, |
| N | is the number cut-offs (sampling lengths) e.g. 2. |
So, if T.n. N is R q2, this means roughness profile, root mean square value taken over two sampling lengths.
For convenience, some values for N have been adopted. These are listed in Table 3.1. If not otherwise indicated on a drawing, the following should be used to determine the cut-off wavelength (ISO 4288). Care has to be taken when using the letter N. Here, this is the number of sampling lengths and not the 'N' value of the surface, which is an old fashioned notation for surface roughness. See the end of this chapter.
| Recommended cut-off ISO 4288 | ||||
|---|---|---|---|---|
| Periodic profiles | Non-periodic profiles | Cut-offs | Sampling length Evaluation length | |
| Spacing distance | R z ( ?m) | R a ( ?m) | ? c (mm) | ? cl (mm) |
| > 0.01 to 0.04 | to 0.1 | to 0.02 | 0.08 | 0.08/0.4 |
| > 0.04 to 0.13 | > 0.1 to 0.5 | > 0.02 to 0.1 | 0.25 | 0.25/11.25 |
| > 0.13 to 0.4 | >... |
Copyright Taylor Hobson Ltd. 2002 under license agreement with Books24x7
