Micro machining is increasingly adopted for manufacturing miniaturized components with high functional integration and stringent surface quality requirements. Due to the comparable scale of tool edge radius and material grain size, chip formation occurs on a grain-by-grain basis, challenging the direct application of conventional machining principles. This study investigates the micro milling of ER70S-6 steel produced via Wire and Arc Additive Manufacturing (WAAM) using Cold Metal Transfer (CMT). The work employed 400 µm (Ti, Al)N-coated tungsten carbide tools at a cutting speed of 6.2 m/min, feed per tooth of 0.50 µm and 4.00 µm, and depth of cut values of 20 µm and 40 µm. Surface characterization was performed through confocal microscopy at magnifications of 5 ×, 10 ×, and 50 ×. Results indicate that cutting depth had negligible influence on surface quality, whereas feed rate significantly affected machining marks. The feed of 4.0 µm/tooth provided the most stable cutting conditions and best surface finish. The inherent microstructural and topographic features of WAAM-fabricated material were also found to be a dominant factor influencing the final surface integrity.