This work consists in designing and constructing na automatic machining system (milling operation) directed to the manufacture of planar photoelastic models with complex geometries. The purpose is to provide the Photomechanic Laboratory of PUC-RIO with an automatic system completely controlled by an IBM personal computer so that experiments on Experimental Stress Analisys with dificult hand-made geometries can be performed. As a means of evaluating the systems perfomance, eleiptical holes were machined in retangular bars made of photoelastic material, and the corresponding stress concentration factors were measuredm, whose analitical solution is well known, for the case of uniaxil tensile loading. Finally, an errior analysis of the imprecisions introduced by the automatic positioning system was carried out, and modifications in order to improve machine quality were proposed.