Coordinate measuring machine (CMM) fixtures are an essential, yet frequently overlooked, part of quality control inspection. Companies generally tend to fixture their parts with whatever methods they deem fit, without regard to how those methods will impact inspection results. The CMM fixture system will not only secure a part for measuring, but will also have the greatest impact on gage repeatability and reproducibility (GR&R) results.
GR&R measures the amount of variability introduced by the measurement system. It is a statistical tool used to determine the variation introduced by the fixturing, the environment, the operators, the measurement program, the part variance, and the measuring instrument. Unfortunately when a GR&R shows variance, the fixturing method is usually the last factor checked.