The complex microstructure of segmented chips and the changing deformation mechanisms during the machining of the Ti-6Al-4V alloy for a given cutting tool have been explored. Chip geometry and microstructure were investigated for increasing volumes of material removed at a cutting speed at which the tool characteristically develops gradual flank wear. The degree of chip segmentation and deformation mode changed significantly as machining progressed from using a new tool towards a worn tool. Chip formation processes when machining near the end of the cutting tool life is characterised by increasing amounts of twinning formed through both tension and compression.