Concentricity is part of coaxiality. While the check of coaxiality includes the axes, the check of concentricity only includes the center point. These checks usually happen several times on a part.
What is concentricity?
Concentricity is referred to as the location check of one or more independent circles. At first, the datum is determined. This datum can be either an axis or a center point. A planar or circular tolerance zone is created around this datum. The location of the center point is allowed to deviate within this tolerance zone. The dimension is considered out of tolerance if the center point is located outside of the tolerance zone.
The concentricity in metrology belongs to Geometric Dimensioning and Tolerancing (GD&T). Position and symmetry tolerances also belong to GD&T. Imagine a washer with an outer diameter of 15 mm. In the center of the washer is a bore hole with a diameter of 10 mm. This bore hole is a datum. The center point of the inner circle is used as a datum at a concentricity tolerance of 0.4. A circle with a diameter of 0.4 mm is created around the datum. This is the tolerance zone in which the center point of the outer diameter is allowed to be in. To achieve concentricity, the center point of the outer circle can only have a maximum radial offset of 0.2 mm to the center point of the inner circle. Otherwise, the center point would be out of tolerance.
The allowed deviations from the basic dimensions (tolerances) develop during the manufacturing process. They often result from systematic or random influences on production, such as temperatures, vibrations or dirt. The information whether the concentricity deviations are within the limit values is crucial for the function of the later part.
Applications of concentricity
The measurement of concentricity plays an important role in the production of precision ball bearings for the automotive and other industries. Rolling bearings are needed in automotive engineering. They reduce the energy consumption due to low friction. The used metrological systems have to work with the highest precision to ensure that the ball bearings have the best possible efficiency. Classic length measurements for ball bearings include:
- Diameter of the bearing groove and bore hole
- Concentricity of bore holes to the outer diameter
- Concentricity of bearing grooves to the outer diameter and bore hole
- Concentricity of seal grooves to the outer diameter
- Roundness of the bearing groove
- Parallelism and location of the bearing grooves to the sides
Ball bearings are built into various products. They enable the smooth and fast rotation of parts that are needed in drive technology, mechanical engineering and machine-tool manufacturing.
Optical 3D measurement technology enables non-contact measurements of concentricity with the help of 3D scans. This enables high-speed measurements with the highest degree of detail.