An automatic lathe produces rollers for roller bearings. The process is monitored by statistical process control charts. The central line for the diameter sample means is set at 8,4 mm, and for the range at 0,31 mm. The process is in control, as established by samples of size 5. The upper and lower specifications for the diameter of the rollers are (8,500,35) mm.

a) Calculate the control limits for the range and mean charts.

b) If the standard deviation of the process distribution is estimated to be 0,09 mm, is the process capable of meeting specifications? Assume four-sigma performance is desired.