Computer Numerically Controlled (CNC) machining of splitblock waveguide circuits has become the primary method of constructing terahertz waveguide circuits. The majority of these circuits have been made on traditional CNC machining centers or on custom-made laboratory machining systems. At both the University of Arizona and Arizona State University, we have developed techniques for machining splitblock waveguide circuits using purpose-built ultra high precision CNC machining centers designed for micromachining. These systems combine the automation of a traditional CNC machining center, including a high capacity toolchanger, workpiece and tool metrology systems and a large work volume, with the precision of custom laboratory systems. The systems at UofA and ASU are built by Kern Micro and deliver typical measured dimensional accuracies of 2-3 microns. Waveguide surface finish has been measured with a Veeco white light interferometric microscope to be Ra~75 nm. Tools of sizes between 25 microns and 10mm are available, with toolchanger capacities of 24-32 tools. The automated toolchanger and metrology systems allow a metal blank to be machined into the final part in one machining cycle, including both micromachining operations and traditional machining operations. This allows for perfect registration between all block features, in addition to very short cycle times. Even the most complicated blocks have machining cycle times of no more than a few hours. Workpiece and tool metrology systems also allow for fast setup times and straightforward part re-work. In addition, other high-throughput techniques such as palletization are enabled for the simultaneous manufacture of large numbers of blocks. Using these machines, we have successfully produced waveguide circuits at frequencies ranging from W-band to 2.7 THz, including highly integrated blocks. The Supercam project relied on these machines to produce integrated 8-pixel SIS mixer array units with integrated low noise amplifiers, bias tees and blind mate connectors. In addition, the 64-way corporate power divider used for LO multiplexing was machined using these techniques. This system consists of 17 split-block circuits containing E-plane power dividers, waveguide twists, diagonal horns and all associated flanges. The final system consists of a single WR-3 UG-387 input and an 8x8 array of 11mm aperture diagonal feedhorn outputs. This is one of the largest submillimeter waveguide circuits ever constructed. Future large focal plane arrays and other applications requiring highly integrated waveguide circuits will critically depend on this type of highly automated micromachining technology. We present the capabilities and machining process used with these machining centers, along with several waveguide circuits that were manufactured with this process including measured results from these circuits. Future directions for improving manufacturing quality and automation for large focal plane arrays will be discussed, including the use of palletization, insitu metrology, and automatic workpiece changers. Using these techniques, construction of the necessary waveguide blocks for even kilopixel class heterodyne array receivers should be realizable in a manageable time with high part yield and relatively low incremental cost.