Control charts for the outer diameter. A sample of 4 skateboard bearings is taken near the end of each hour of production. Given Table gives x and s for the first 21 samples, coded in units of 0.001 mm from the center of the specifications. The specifications allow a range of ±0.015 mm about the center (a range of -15 to +15 as coded).
(a) Make an s chart based on past data and comment on control of short-term process variation.
(b) Because the data are coded about the center of the specs, we have a given target μ = 0 (as coded) for the process mean. Make an x chart and comment on control of long-term process variation. What special x‾ -type cause probably explains the lack of control of x‾?