Measuring Waviness

Technical Data Sheet #13

The quality of our precision balls is guaranteed by the finest Metrology department in the industry. The versatile waveometer can make measurements as fine as 1/20 of a millionth of an inch. On balls of very high quality or balls for special applications, there may be a waviness requirement in addition to the sphericity and surface roughness.

In general, waviness is made up of those imperfections in the surface of the sphere that occur more frequently than the basic geometry but less frequently than the surface roughness. This characteristic is measured with a special instrument called a waveometer. The waveometer rotates the test ball on an almost perfect spindle. The flat plastic tip of an electronic pickup is brought into contact with the rotating ball. The pickup transforms mechanical variations around the surface of the ball into electrical variations.

These variations are amplified and then sorted into two groups according to how often they occur. The low band looks at variations that occur from 4-17 times per revolution, and the high band looks at those that occur from 17 to 330 times per revolution. The RMS value of the waviness is read out directly in microinches in each of the two bands. The instrument incorporates an Oscilloscope that draws an electrical picture of the circumference of the ball. This allows the operator to analyze the actual nature of the waviness.