Preliminary Comparative Assessment of Hole Quality and Geometrical Tolerances in AM-Built and CNC-Drilled PLA Components

The increasing adoption of polymer additive manufacturing (AM) in functional applications has intensified the need for reliable hole-making strategies, particularly when printed components require mechanical fastening or post-processing. However, the layered architecture of fused-filament fabrication (FFF) parts typically leads to dimensional inaccuracy and thermally induced defects during drilling. This study examines the quality of holes made directly with FFF technology and those obtained through traditional drilling on polylactic acid (PLA) components produced with two different layer heights (0.20 and 0.28 mm). Additively manufactured holes were analysed via least-squares circle fitting and roundness evaluation, revealing high repeatability but substantial undersizing (>1 mm deviation from the 6.35 mm nominal diameter). CNC drilling tests were then performed under a full-factorial combination of spindle speed and feed rate, assessing thrust force, torque, infrared-based cutting temperature, and burr formation for both top and bottom sample side. Results show that CNC drilling can restore near-nominal dimensional accuracy, but only within a restricted process parameters window. Low feed rates promote severe thermal-viscoplastic deformation, while specific combinations of spindle speed and entry surface strongly influence burr formation.