We report on progress developing the 'Precession Process', that has recently been embodied for the first time in a fully-productionised aspheric polishing machine. We describe how the process uses inflated polishing tools of continuously-variable size and hardness. Despite the rapid tool-rotation needed to give high removal rates, the method produce well-behaved and near-Gaussian tool influence-functions, by virtue of the precession of the spin axis. We then describe how form-errors are controlled. The method takes influence-function data and an error-map as input, together with, uniquely, weighting factors for height and slope residuals and process-time. A numerical optimisation of the cost function with variable dwell-time, tool-path and tool-size is then performed. The advantages of this new technique are contrasted with conventional deconvolution methods. Results of form-control on aspheric surfaces are presented, with an interpretation in terms of spatial frequencies. We draw particular attention to control of form at the centre and periphery of a work-piece. Finally, we describe how Precession processing gives multi-directional rubbing of surfaces, and we present the superb texture achieved on samples.
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