Different possible reasons for defects have to be considered in machining light-weight aluminum structures. In the machining process, the cutting power affecting the workpiece leads to a thermo-mechanical load that can cause undesirable workpiece deformations and thus shape deviations. Moreover, the microstructure and the machined surface can be influenced, which is detrimental to the later application of the structures. Previously conducted experimental and simulative investigations, estimated the circular milling process to be the most suitable machining operation that provides the best compromise between mechanical and thermal loads compared to drilling operations [1,2]. In this paper the results of machining end-cross-sections of an aluminum profile are presented. The machining was obtained by a milling process, which is demanding, because of the low profile stiffness. For this process it is important to know the effects of machining in view of the shape deviations. By means of a Finite-Element-Analysis the deformations of the profile web can be calculated as well as validated by experiments. Based on these results, the appropriate process parameter values for end machining can be defined.