Nowadays, the micro-factory concept of downsizing production systems is essential to manufacturing small products in sustainable growth. Concerning this, this paper presents the developments accomplished during the recent years at Tecnológico de Monterrey (Mexico) introducing new findings related to the design of reconfigurable micro-machine tools for micro-factories. It shows the framework related to the conceptualization of micro-factories for manufacturing system layouts based-on reconfigurable micro-machine tools, identifying the basic steps. The methodology for designing reconfigurable micro-machine tools is exposed, and a reconfigurable first-generation CNC micro- machine tool for micro-factories, is designed and tested, using the Universal Numerical Control concept.