Hellstrand (1989) reported on a 2³ experiment carried out by SKF, a manufacturer of deep groove bearings. The factors were inner ring heat treatment, outer ring osculation d cage design, and the response was life (hours) of the bearings determined in an accelerated life test procedure. For each factor the levels were standard and modified, with standard representing the current level for production of the type of bearing. The data are displayed in Table 8.33 and are reproduced by permission of The Royal Society, London.

• Use Minitab to display the data in the form of a cube plot and to display an interaction plot for the heat-osculation interaction effect. (In setting up the design using Minitab, uncheck Randomize Runs under Options..., so that the factor-level combinations will be in standard order as in Table 8.33.) Box (1990, p.367) commented that the experiment 'led to the extraordinary discovery that, in this particular application, the life of a bearing can be increased fivefold if the two factors outer ring osculation and inner ring heat treatments are increased together' .

Table 8.33: Data for bearing life experiment Heat Osculation Cage Life Standard Standard Standard 17 Modified Standard Standard 26 Standard Modified Standard 25 Modified Modified Standard 85 Standard Standard Modified 19 Modified Standard Modified 16 Standard Modified Modified 21 Modified Modified Modified 128