"People use to be happy making parts to print tolerance," said Greg Hyatt, manager of the product and process development group at Makino Inc. (Mason, OH). "Now those tolerances meet no one's expectations. Manufacturers are pursuing statistically capable processes and often tighter tolerances on the same print."
To satisfy Six Sigma requirements, operations performed on machining centers and milling machines must perform to within ten-thousandths of an inch, even though a print might specify only to within thousandths. The situation becomes more extreme when print tolerances are tighter. Consequently, the temperatures of the workpiece and the machine's internal components are affecting the machine's ability to hold tolerances more significantly than in the past.