“…The direct free boundary problem for the Laplace equation has been solved through conformal mapping (assuming constant conductivity) for a few special cases by Collett, Hewson-Browne, and Windle [1] and by Dietz, Gunther, and Otto [2], whereas Tipton [15] describes a finite difference procedure, and Kawafune, Mikoshiba, and Noto [8] suggest constructing an analogue model. The socalled cosine law of machining which appears extensively in the literature is a first order approximation for the inverse free boundary problem which has been solved exactly by Krylov for some mathematically tractable geometries.…”