To avoid any high-speed imbalance in a rotating shaft; it needs to have a variance of its diameter below 0.0004 mm2. The shaft diameter has been measured at 16 equally distributed locations, with a standard deviation of 0.018 mm. (a) Determine the confidence interval on the variance of the diameter along the shaft with a 95% confidence level.
(b) With a confidence level of 95%, is this shaft acceptable to the customer? (That is is the variance in diameter along the shaft below 0.0004 mm2?)
(c) Answer the questions in Parts (a) and (b) if five measurements are done and the same standard deviation is calculated.