This article examines the relationships between the quality of a machined component and the non-intrusive measurements that can be made during the manufacturing process. For the purposes of this study, the overall quality of a machined component is defined by the surface finish and any residual stress induced by the machining process. The focus of the work involves turning of difficult-to-machine metals and non-intrusive measurements recorded during machining. These measurements were acoustic emission, cutting forces and cutting insert temperature. An austenitic stainless steel was chosen as a commonly available metal whose high work-hardening rate and ability to strain transform to martensite make it potentially difficult to machine. Tests were carried out under different cutting conditions to promote thermally and mechanically induced residual stress and variations in the surface finish. Analysis of the mean frequency of the acoustic emission signal has made it possible to determine whether thermal or mechanical interactions dominate the machining process. The mean frequency of the machined samples provided evidence of a thermally driven process. This was confirmed by the close relationship between cutting insert temperature and component residual stress. The analysis of low-frequency acoustic emission generated during machining (below 100 kHz) identified poor surface finish derived from vibrations of the cutting insert.