The Nanosphere coating, which is under patent application and available on gear hobs from LMT (UK) of Coventry, can be applied to high speed steel as well as carbide cutters. It not only insulates the tool like a heat shield but also reacts ‘elastically’ to protect the hob teeth from the high thermal and mechanical stresses generated during the gear hobbing process. The new coating has a distinct advantage over normal nitride coatings where the arduous cutting operation can lead to the so-called ‘eggshell’ effect where, under high temperatures, the single hard surface of the coating cracks and separates from the softer substrate of the tool. It then tends to flake back in similar vein to an eggshell which leads to a dramatic reduction in the cutting life of the tool. LMT’s engineers describe how the four micron thick Nanosphere multi-layer coating surrounds the tool like a ‘layer of rubber’. This has the effect of slowing down any thermal reaction during the gear cutting process between the materials being cut, the chip and the hob’s teeth, thus extending the time taken for the substrate to heat up. At the same time, the elasticity of the multi-layer coating enables it to move with the substrate and so overcome any influence from loss of stability in the cutter created by the process.