Round robin comparison measurement of a camshaft standard

The measurement of camshafts has not yet been standardised. In order to determine the state of the art in the measurement of camshafts and to create a basis for possible further pre-normative work, PTB has carried out an intercomparison with interested parties from the circle of measuring instrument and camshaft manufacturers.

For this purpose, a camshaft standard developed in an earlier project was measured by the participants with coordinate measuring machines and specialised shaft measuring devices. Numerous measured variables were determined on the bearings, eccentric discs and cams of the standard. Due to the lack of normative specifications, the participants were to carry out the measurements and evaluations according to common practice in each case in order to represent the current situation as well as possible.

The measured values of the PTB were defined as reference values.

It turned out that the deviations of the participants from each other and especially from the PTB in most cases meet the requirements of the industrial final product. However, simple geometric elements such as the bearings and circular eccentric discs were significantly better controlled than the complex geometric cams. Figure 1, for example, shows that the measured values of various measured variables at bearing L1 scatter only very slightly. The majority of the measured values lie within an interval of ± 1 µm. In comparison, Figure 2 shows the scatter of different cam measured variables at cam N2. Here, most measured values lie within an interval of ± 2 µm. However, the results of some participants are more than ± 1 µm away from the reference value. The discussion of the results showed that establishing a reference for cams is a great challenge.

Fig 1: Scatter plot of the measured values of different measured variables at bearing L1. The participants of the comparison are colour-coded. The evaluated measured variables are plotted on the X-axis.

Fig 2: Scatter plot of various measurands of cam N2