Stop X-bar/R Madness!!
One of the things that is unclear with Shewart charts is the frequency of charting. However, with the X hi/lo chart for precision machining, the frequency can actually be calculated. Attached is the Excel calculator for determining frequency. The tool wear rate is based on the linear regression of either the Hi or Lo line of the X hi/lo chart. The resolution is the number of points between adjustments based on the stated tool wear rate. Roundness in the typical amount of roundness for that process.