The machinable spectrum of materials by micromilling is broad (metals, polymers or ceramics) but yet, considering steels, limited to a certain hardness of around 50-55 HRC for commercially available microtools mainly due to the tools reduced stiffness. When cutting with diamond tools, another restriction for an economical process is that till date, the workpiece is nonferrous [20].

The micro-cutting of steel has recently received strong research interest with the initiation of miniaturised systems using a variety of materials, especially for biomedical applications and injection moulds. The most commonly used tool steel is 1.2343 (X38 CrMo V5-1), which can be hardened to 54 HRC.

Chemical reactivity with the cutting tool, crystal structures, defect distribution, and heat treatment are some factors that could affect the micro-machinability. It should also be considered that the material combined with the geometry of the part ought to be rigid enough in order to present a minimum distortion when clamping.

The assumption of homogeneity in workpiece material properties is no longer valid because micrograin size is often of the same order of magnitude as the cutter radius of curvature [64].

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