17.46 Control charts for the outside diameter. A machine tool in your plant is cutting an outside diameter. A sample of 4 pieces is taken near the end of each hour of production. Table 17.9 gives x and s for the first 21 samples, coded in units of 0.0001 inch from the center of the specifications.

The specifications allow a range of ±0.0002 inch about the center (a range of −2 to +2 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 TABLE 17.9 x and s for samples of outside diameter Sample x s Sample x s 1 −0.14 0.48 12 0.55 0.10 2 0.09 0.26 13 0.50 0.25 3 0.17 0.24 14 0.37 0.45 4 0.08 0.38 15 0.69 0.21 5 −0.17 0.50 16 0.47 0.34 6 0.36 0.26 17 0.56 0.42 7 0.30 0.39 18 0.78 0.08 8 0.19 0.31 19 0.75 0.32 9 0.48 0.13 20 0.49 0.23 10 0.29 0.13 21 0.79 0.12 11 0.48 0.25 variation. What special x-type cause probably explains the lack of control of x?