Spatial Cutoff Filter

Wavelength Separation

Filtering divides the complex surface profile into distinct, analysable components based on spatial frequency. High-frequency variations are associated with fine textures, whereas low-frequency waves represent larger-scale form deviations. The selected cutoff wavelength acts as the dividing line for this analysis.

Choosing the wrong cutoff can lead to inaccurate roughness measurements, masking critical defects. For instance, a cutoff that is too large might blend structural waviness into the roughness calculations, giving an artificially high average roughness value. Conversely, an excessively short cutoff can omit important micro-textural details that define the cosmetic quality of the polymer part.

Measurement Application

Different surface textures require specific cutoff values to ensure repeatable data. Smooth, high-gloss parts use short cutoffs to focus on micro-defects like orange peel. Heavily textured parts require longer cutoffs to properly capture the molded grain without distortion.

Standard ISO and ASME guidelines specify these settings based on the expected surface finish.

Process Diagnosis

Isolating these wavelengths helps identify the root causes of moulding defects. High roughness often points to a worn mould surface or low melt temperature. Waviness, on the other hand, usually relates to non-uniform cooling or packing.

By applying the correct spatial cutoff filter, metrologists can pinpoint which process variable requires adjustment.