A portable and transportable die cavity modifying machine having a base carrying a carriage adjustable along one axis, e.g., a generally horizontal axis, and a machining head adjustable along another axis, e.g., a generally vertical axis, for modifying a die cavity of a stamping die in a manner that prevents blank or slug pulling during stamping press operation. The machine includes a grinder that can be pneumatically powered having a grinding bit used to precisely machine a slug retention groove in a die cavity defining surface (sidewall) of a die cavity formed in a stamping die. The machine has an angularly adjustable head carrying the grinder enabling adjustment of the angle of the groove relative to die cavity defining surface enabling the groove to be angled relative to the direction of a punch entering the die cavity during stamping.