A detailed study of the fluid flow and thermodynamic processes in positive displacement machines requires 3D CFD modeling in order to capture their real geometry, including leakage gaps. However, limitations in the conventional computational grids, used in commercial software packages, exclude their use for classical twin screw machines. The screw compressor rotor grid generator (SCORG) is a customized grid generation tool developed to overcome these limitations. This paper shows how it can be further extended to include non-conventional rotor designs, such as those with variable lead or profile variation and even internally geared machines with conical rotors. Other arrangements possible with this improvement include multiple gate rotors to increase volumetric displacement or dual lead, high wrap angle rotors for very high-pressure differences and vacuum applications. A case study of a water-injected twin screw compressor is included to demonstrate its use for both detailed flow analysis and design.