Waviness is the measure of the more widely spaced component of surface texture. It is a broader view of roughness because it is more strictly defined as "the irregularities whose spacing is greater than the roughness sampling length". It can occur from machine or work deflections, chatter, residual stress, vibrations, or heat treatment.[1][2]
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There are many parameters for measuring waviness. One of the most important is the waviness evaluation length, which is the length in which the waviness parameters are determined. Within this length the waviness profile is determined. This is a surface texture profile that has the shorter roughness characteristics filtered out, or removed; it also does not include any profile changes due to changes in workpiece geometry. From this profile the waviness spacing, which is the average spacing between waviness peaks, is determined. The waviness height is also determined from the profile, which is just the height from the top of the peak to the bottom of the trough. It is usually at least three times the roughness average height.[2][3]
Waviness is not part of any ISO standards, but it is part of the surface texture symbol used in engineering drawings.[4]
The measurement of the waviness can be done with a variety of machine, such as a waveometer or a microtopographer. A waveometer uses a plastic tip that is connected to an electronic pickup which then measures the surface variations. The measurement is recorded as an electronic signal which is amplified and split into two signals: a high band and a low band. For measuring a ball bearing, the low band signal records variations that occur ever four to seventeen times per revolution and the high band signal records variations that occur seventeen to 330 times per revolution; the low band is the waviness. These bands are transmitted to an oscilloscope for analysis.[5][6]
Waviness measurements are not as common as roughness measurement, however they are important in applications. For example, waviness in bearing balls and bearing races is one of the reasons for vibrations and noise in ball bearings.[7][8][9]