# A Novel Slicing Strategy to Print Overhangs without Support Material
## 3 Results  
Cubes with no overhangs have been printed to evaluate the slicing strategy. Figure 11 shows the cone shaped layer of a cube with a radial orientation of the nozzle and Figure 12 the finished cube with the strands on the surface following a hyperbolic curve. The picture indicates a reasonable quality with this slicing approach. Nevertheless, the surface quality is not yet at the level of parts printed on x-y-z printers due to the lack of optimization of the slicing software for a 4-axis kinematics. Figure 13 shows the top surface of a cube with artifacts, due to too big triangles in the STL file, as described in Section 2.2.1. The slicing strategy also proved to work unproblematically for more complicated parts with 90\({}^{\circ}\) overhangs and holes. Figure 14 shows such a part being printed with the nozzle oriented in radial direction. Figure 11: Printing a cube with a radial orientation of the nozzle. Figure 12: Finished cube, with a radial oriented nozzle. Several papers investigate the impact of different parameters on the dimensional accuracy and the surface roughness of FDM printed parts ([7; 25; 26; 27; 28; 29; 30]. To date, no fully comprehensive series of measurements have been conducted with the novel slicing strategy presented regarding the various influencing parameters. With a limited number of tests, a set of reasonable printing parameters could be found (Section 2.3). A reference geometry (Figure 15) has been printed with these settings on the RotBot and with corresponding settings on a Prusa Mk3s to compare the geometrical accuracy and the surface roughness (Table 1). For a quantitative comparison, the parts have been 3D scanned with a HandySCAN 3D scanner and evaluated with the VXElements software from Creaform. The scanning  
Figure 14: Part with outside overhang and holes being printed. Figure 13: Top surface with artifacts, due to large triangles. accuracy has been set to a maximum of 50 \(\upmu\)m. The measured geometry shape has then been compared with the CAD geometry, using the software Gom Inspect. Figure 16 shows the deviation from the scanned parts and the CAD file. The part printed on the Prusa (left) has a deviation between approximately \(-0.1\) and \(+0.1\) mm. Downward overhangs have the biggest offset with a deviation of up to 0.5 mm. The part printed on the RotBot (right) has a higher deviation of about \(-0.2\) to \(+0.5\) mm. The maximum offset in this part can be found on the edges. The reduction of the material flow and an adjusted calibration of the nozzle could help to reduce the offset. 3 different surfaces (marked in Figure 15) of the two reference parts have been scanned with a confocal z scan (150 \(\upmu\)m) on a Leica DCM 3D microscope with an EPI 20X-L objective to quantify the surface ripple and in particularly its roughness. 9 individual surface scans have been stitched together to reach a representative area with the high magnification. This leads to surfaces of about 1.3 \(\times\) 1.7 mm. This surface scans, all with the same color scale, and close up pictures showing the same surfaces for a visual evaluation of the quality are printed in Figures 17-22. Figure 17 displays the parallel layers of the part printed on the Prusa and the conical shaped layers of the part printed on the RotBot. The Prusa printer shows a higher regularity to the eye. Figure 18 illustrates the ripple and the roughness of the vertical surfaces with the horizontal layers. The measured values are shown in Table 2. It reveals that both reference parts have very similar values. Figure 16: Shape deviation (CAD vs. print) on Prusa (**left**) and RotBot (**right**). Figure 17: Horizontal layers of the printed reference part printed on a Prusa Mk3s (**red**) and the RotBot (**orange**). Figure 18: Roughness scan of vertical surface of reference parts. Prusa (**left**) and RotBot (**right**). The Figures 19 and 21 provide a closeup of the surface of upward and downward horizontal planes.