Large-load-capacity oil hydrostatic bearings generate prohibitive amounts of heat in large sizes when run at speeds useful for diamond turning of optical components. The viscosity of air is more than three orders of magnitude less than the thinnest oil; therefore, the frictional heating of large-diameter air bearings is very small and very manageable. A formidable manufacturing problem with large air bearings is that the extremely low viscosity of air requires that the thickness of the bearing film is also very small. This very small bearing clearance of 5-8 micrometers means that the required accuracy of geometry and dimensions of air bearing components is extremely difficult to achieve.
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