A three-axis micro CNC milling machine was developed for manufacturing mesoscale components and products, and the experiments of end-milling brass were performed on the developed machine. The experimental results show that: when the machined feature range is at mesoscale, the process phenomena and mechanical characteristics in milling operations can heavily differ from conventional scale milling due to the size effects; the relatively large ratios of cutting edge radius and spindle’s runout to feed per tooth, which induce the intermittency of the chip formation at a low feedrate, have an important influence on the mesoscale milling mechanism and forces characteristics; the feed per tooth is not a constant in the given cutting condition, but a function of the spindle’s runout, the minimum chip thickness and the cutting condition.