Mechanical errors

Precision manufacturing processes rely, primarily, on mechanical devices and structures as the basis of their operation. We saw the machine tool structural loop connecting the cutting tool to the workpiece through the spindle, machine overarm, column, base and table and through the work fixture. Shirley and Jaikumar identified error sources with respect to part and machine contributions to systematic and random/dynamic errors. These systematic errors were detailed in Figure 2.3 and the environmental and process influenced (often dynamic or random) were shown in Figure 2.4. Of course, the way a machine behaves in the production of a surface or a form on a workpiece reflects the combination of a number of these sources of error. This chapter will review the mechanical error sources in machines. Chapter V will do a similar review but from the point of view of thermal error sources in and out of machines. Then, Chapter VI will describe a methodology for combining the particular error sources with the particular machine structure or configuration to estimate the limits on the machine accuracy.