Firstly, failures of the ram feed subsystem are organized by the extended FMECA. Part of the extended FMECA worksheet is displayed in Table 3. Herein, the third column shows the failure classification which is specified in Table 2. The fourth and fifth columns indicate the severity and detectability rating respectively. Moreover, Tables 4 and 5 display the rating criteria defined by the experts of CNC machine tool. Se and De in the last column of Tables 4 and 5 indicate the fuzzy severity and detectability respectively. The cause list in the seventh column of Table 3 uses the parenthesis to represent the concurrent cause. The percent list is provided in the eighth column.