How arc elimination works in measurement practice

When measuring over a circular arc, the roughness profile does not run through the center of the X-axis of the profile plot when filtering with the Gaussian filter. For convex radii, the roughness profile lies above the X-axis, for concave radii below the X-axis. However, this leads to incorrect measurements for roughness parameters that are influenced by the distance of the profile from the X-axis.
With the MarWin EasyRoughness and EasyContour software solutions from Mahr, the "Arc elimination" function can be used in these cases: This filters out the arc from arc-shaped profiles that have been recorded on convex or concave measurement objects. This is necessary in order to be able to correctly determine the required surface parameters: "Arc elimination unwinds the arc in the original D-profile so that the P-profile is displayed as a linear profile with its waviness and roughness components," explains Timo Dankenbrink, Head of Application Technology at Mahr. "The arc elimination takes place before the actual profile filtering with the Lc filter. After the subsequent filtering with the Gaussian filter, the roughness profile runs through the center of the X-axis."

"Arc" selection box
From software version v14.50-03, Mahr now offers even more options for eliminating arcs.With the "Arc" option, you first select in the selection box that the arc elimination is to be carried out. The following options are available:

• not active (default setting) → no arc elimination
• before filtering, perpendicular to measuring plane
• before filtering, perpendicular to susbtitute element

Important: This step is currently not standardized. However, Mahr offers the following two options to make it easier to compare measurement results:

▶ Selection "Before filtering, perpendicular to measuring plane"

This option calculates the values in the direction of probing, i.e. perpendicular to the measuring path, back to the replacement elements. Consequently, the correction is made in the Z direction. This is the setting recommended by Mahr if the angular segment of the arc over which the measurement is made is not too large, as otherwise deviations may occur on the steep slopes.

▶ Selection "Before filtering, perpendicular to substitute element"

This option recalculates the values perpendicular to the substitute element, i.e. the arc. It is recommended for slopes > 66°, i.e. over large angular segments of an arc.

Do you need detailed information about the diverse measurement and evaluation strategies used in industrial practice with Mahr roughness and contour measuring stations? Take advantage of our Level 2 application technology training courses!
Do you have any questions? If so, Timo Dankenbrink, Head of Application Technology at Mahr, will be happy to help you at +49 (551) 7073-99499 or timo.dankenbrink@mahr.com.