Laser induced, micro-chemical etching is a promising new technology that can be used to fabricate three dimensional structures many millimeters across with micrometer accuracy. Laser micromachining possesses a significant edge over more conventional techniques. It does not require the use of masks and is not confined to crystal planes. A non-contact process, it eliminates tool wear and vibration problems associated with classical milling machines. At the University of Arizona we have constructed the first such laser micromaching system optimized for the fabrication of THz and far IR waveguide and quasi-optical components. Our system can machine many millimeters across down to a few microns accuracy in a short time, with a remarkable surface finish. This paper presents the design, operation and performance of our system, and its applications to waveguide devices for sub millimeter and far IR interferometry.