Composite materials are alternative materials to aluminum and titanium alloys. The wide-spread use of this materials makes it necessary to gain insight into the phenomena occurring in machining processes for thin-walled structures. This paper shows the investigation of the machinability of thin-walled composite materials. The study involved milling glass and carbon reinforced plastics using tools dedicated to the processing of this type of material. Their machinability was determined based on the measured feed force, deformation and surface roughness. In addition, surface analysis was performed by SEM. The results showed that the feed had the greatest impact on the feed force, deformation and surface roughness, followed by cutting speed. Lower values of the measured machinability indicators such as the maximum feed force and roughness were obtained for composites with glass fibers. Lower deformations were induced in the machining of composites with carbon fibers. The study also involved conducting a recurrence analysis in order to select the most appropriate quantifications depending on the technological parameters of milling. It was found that the most appropriate indicators related with the technological parameters for both materials were laminarity and averaged diagonal length.