Advances have been made in the art of metal cutting, much to the economic benefit of industrialized nations. Not withstanding this, engineers continue to seek stronger and lighter materials. New challenges emerge as we seek to understand and control the deformation of a small volume of material in the immediate vicinity of the cutting edge. In this paper we use a metallurgical approach to explore and understand the nature of high strain deformation in light metals and its influence on the chip forming process. In particular the phenomenology of material flow around the cutting edge is discussed on the basis of previous studies of machining in the SEM. The issue of chip separation is discussed, particularly in relation to its impact on the tribology of the ship / tool / workpiece interface. The objective is to better design cutting tools and their vapour deposited coatings for improved machinability in light metals.