Full calibration of a CMM's performance is time consuming and costly, using fixed length ball-ended bars or step gauges and laser measurement systems.
Renishaw's MCG (machine checking gauge) enables the rapid and effective interim checking of a CMM's performance as recommended in many international standards. It gives a fast and automatic assessment of machine capability and can also be used for machine characterisation.
- MCG arms of lengths 101 mm, 151 mm, 226 mm, 380 mm
- Pillars of height 76 mm, 127 mm and 235 mm
- Hex key and balance weight
- Calibrated test stylus
- User's guide
- Stylus and pivot ball roundness trace
- System dynamic test certificate
An MCG kit consists of a base, a calibrated pivot point (with various pillar height options) and various length counterbalanced arms.
The counterbalanced arm has a seat which locates on a precision ruby ball on an adjustable pillar. The seat allows very accurate arm pivoting, through 360° horizontally and ±45° vertically. At the end of the arm is a second location, formed by the two rods, a tungsten carbide ball and specially calibrated stylus which is fitted to a Renishaw probe. The CMM's probe stylus slots into the end of what is in effect a reference "ball" bar.
The arm is able to describe a truncated sphere of radius R (see illustration) about the pivot. As the arm is of constant length, any deviation from radius R is an indication of the volumetric measuring performance of the CMM. Repeatability can also be determined by performing multiple runs and comparing measured radius values at the same locations.
Volumetric measuring performance is the maximum error between any two points in any plane, over any distance within the full measuring volume.