Machining hollow cylinders

A process comprising

• providing a hollow cylindrical substrate, the substrate having a dry outer surface describing a curvilinear plane, a dry inner surface describing a curvilinear plane, a first end opposite a second end, and an imaginary axis extending from the first end to the second end;
• supporting the substrate;
• machining at least a portion of the end of the substrate with a dry polycrystalline diamond cutting tool situated near the end of the substrate and in the absence of liquids to liberate machined debris material from the substrate;
• and
• simultaneously maintaining, during machining, the dry inner surface of the cylindrical substrate free of the liberated machined debris by continuously flowing sufficient air to carry away the liberated machined debris from the substrate, wherein the sufficient air flow is accomplished by continuously vacuuming the liberated machined debris from the machined substrate, and wherein the cutting tool and the portion of the cylindrical substrate contacted by the cutting tool are enclosed in a vacuum housing connected to a source of vacuum.