A three-dimensional printer with improved adjustment mechanisms for calibrating the orientation of the build platform and an extrusion assembly to optimize the accuracy of models deposited on the build platform. The printer includes a frame carrying an extrusion assembly proximate the top, and a carriage within. A build platform is mounted on the top of the carriage. Carriage adjustment mechanisms are provided at at least two corners of the carriage for calibrating the orientation of the build platform with respect to the X-Y plane. An extrusion assembly adjustment mechanism is provided at at least one end of the extrusion mechanism for calibrating the orientation of the extrusion mechanism with respect to the Y-axis. A height adjustment mechanism is provided for translating the carriage within the frame along the Z-axis.