This research work deals with the development of a methodology for the preliminary assessment of hardness, fatigue, and crack propagation performance of plastic parts manufactured employing polylactic acid (PLA), deposited layer by layer using Fused Filament Fabrication (FFF) technology. A commercial polylactic acid filament was used to print different sample geometries to assess shore D hardness and its correlation with raster direction angles of 0°, 0°/90°, and 0°/45°/− 45°, relative to a reference point, and with three different heat treatment temperatures namely 60 °C, 100 °C, and 140 °C. Additionally, fatigue life and crack propagation were assessed as a function of raster direction angle. Finally, a statistical modeling methodology was employed to obtain both linear equations and response surface plots to correlate performance with layer orientation and heat treatments. The results showed that samples produced at 0°/90° and 0°/45°/− 45° raster direction angles and heat-treated at 100 °C showed the highest hardness performance. Also, the samples produced at 0°/45°/− 45° raster direction angle showed the lowest crack propagation rate until a 200 µm length was achieved, after that the crack rate increased abruptly, reaching 1500 µm at around 4500 fatigue cycles; the 0°/90° raster direction angle reached a crack length of approximately 800 µm at the same number of cycles. The fatigue results showed that samples printed at 0°/45°/− 45° raster direction angles showed a fatigue life of 18,505 cycles, which is above the fatigue life found in samples produced employing the 0° and 0°/90° raster direction angles. The statistical analysis derived from the obtained results shows that the raster direction angle is key to defining the bulk properties of the 3D-printed PLA parts. It was also demonstrated that the use of statistical modeling is a design alternative in contrast to the theory of laminates for composites, which is worth studying and developing for the manufacturing of mechanical parts by 3D printing.