This paper describes a new efficient method for computer aided optimisations of micro EDM die sinking tools, which can be used for design optimisation and performance verification in the digital domain. This would facilitate the integration and re-configurability of the micro EDM die sinking process in high value products manufacturing chains. An EDM simulation tool which makes use of voxels embedded in a voxel octree to represent the geometries is introduced and its application to a new Micro-EDM die-sinking tool shape optimisation is then described. Simulation results obtained with simple shapes are then discussed highlighting the capabilities of the new optimisation method and potential areas of improvement are proposed.