Preprocessing and Filtering

1
Preprocessing and Filtering

• Form Removal
• Filtering of Profiles
• 2RC and ISO Filters
• Bandwidth and cut-off

2
Constituents of Surface Texture
From ASME B46
3
Surface Texture Measurement and Characterization

• Profile Measurement
• Preprocessing
• Filtering
• Numerical Evaluation
• - Roughness Ra
• - Waviness Wa
• - Profile Pa

4
Source ASME B46
5
Form Removal
Straight-Line Nominal Profile
Curved Nominal Profile
6
Source L. Mummery, Hommelwerke
7
Sampling Length () Assessment Length
(L) Traversing Length
8
Selection of cut-offs
Source Tabenkin, Federated Products Corp.
9
Wavelength Transmission Limits
Source ANSI B46.1 - 1985
10
2RC Filter Transmission Characteristics
11
Distortion produced by the standard filter of
waveforms whose period is only slightly smaller
than the cut-off.
Source R. E.Reason
12
Gaussian Filter
13
Gaussian Transmission Characteristics together
with the Nominal Characteristic of a 2m Stylus
14
ISO/DIS 4287-1.21994(E)
Transmission band for roughness and waviness
profiles
15
Standard cut-off for Gaussian Filters and
Associated cut-off Ratios
With a nonstandard stylus of 0.5 mm, the
cut-off ratio for lc 0.08 may be equal to 100
provided ls 0.8 mm and the maximum point
spacing 0.16mm. With a nonstandard stylus
of 0.5 mm, the cut-off ratio for lc 0.25 may be
equal to 300 provided ls 0.8 mm and the
maximum point spacing 0.16mm
Source ASME B46
16
Cut-off Values for Profiles using Sm
17
Cut-off Values for Non-Periodic Profiles using Ra
18
Surface Texture Symbols
Max Waviness Height
Max Waviness Width
0.002.-2
Max Ra
63 32
cut-off Lay
0.030 0.015

Min Ra
Max Roughness Spacing
19
Lay Symbols ASME Y14.36