The economical (fast) fabrication of large aspherics that have departures from the nearest sphere ranging up to several millimeters requires aspherization by grinding methods rather than polishing methods. One grinding method is the high-precision machining of the aspherics with fixed diamonds on a uniaxially controlled machine. Following aspherization, polishing can be accomplished with suitably flexible tools, ideally in conjunction with a computer-controlled polisher. The Optical Sciences Center has in operation two such machines: the Large Optical Generator (LOG) and the Swing-Arm Generator (SAG) . Both machines, relying on quite different tool-path geometries, can cut large and fast aspherics to about 1-ttm RMS surface accuracy, which brings the surface to well within the capability of polishing tools to reach typical final-figure accuracies. To take full advantage of this machine accuracy, the resulting surfaces must exhibit sufficient smoothness to minimize the post-generation fabrication effort. Clearly, the less surface damage the less effort will be necessary. However, the surface finish is not the most important consideration when determining the next step. Rather, it is the depth of the subsurface damage caused by the diamond. This damage must be removed in subsequent operations to produce a surface having the least amount of scatter and the highest mechanical strength achievable. During the fabrication of a 40-in.-diameter Zerodur off-axis parabola on the LOG and a 27-in. Zerodur off-axis parabola on the SAG, we evaluated the subsurface damage throughout the generating process using the contact method described below for each grade of diamond that was utilized.