# A Novel Slicing Strategy to Print Overhangs without Support Material
## 4 Discussion  
Section 3 proofs, that the approach works in general but that the quality is not yet on the level of conventionally produced FDM parts. One reason for this is that conventional slicing software is optimized for the x-y-z kinematics. For example, a top layer is treated differently by the slicer than a perimeter. Transforming the G-code back, a perimeter can become a top layer and vice versa. Further research and testing for the slicer settings is required to improve the quality of the prints. At the moment it is not possible to distinguish whether it is mainly the hardware or the slicing strategy that causes the main quality losses.  
Beside the quality issues, there are other topics worthy of further investigation:  
* The refinement of the triangles is done with a very simple approach. This leads to unoptimized STL files. The refinement should be done in a way, that only the bigger triangles are refined until all triangles are small enough to fulfill the requirements. To keep the number of triangles low, the already small triangles must not be affected.
* As stated in Section 3, the movement of the RotBot needs further improvement. The optimal speeds, accelerations and jerks of the different axes have to be optimized for the reduction of the printing time and constant printing quality.
* As described in Section 1.2, more complicated geometries with a combination of overhangs to the inside and the outside direction must be separated and sliced independently. Up to now, this only has been done manually with very simple combinations as shown in Section 3. Further research and testing have to be done to manage a variety of different geometries, with the aim of an automated analysis and separation.
* Parts that can be sliced with only one outward transformation do not have any collision problem, since the printhead always is on the outside of the cone. However, parts with inward cones and parts with a combination of different cones do face collision problems. This has be investigated further and solutions have to be developed.
* The Python file for the back-transformation is optimized to work with G-codes from one defined slicer (Simplify3D). Other slicers could include commands into the G-code that are not handled correctly with the Python script. One example are the comment lines, which are used in the back-transformation script to differentiate between infill and perimeter. Therefore, a more generic Python script has to be written.
* It should also be considered to develop a completely new slicer software optimized for the conical layers. This would prevent the geometric transformation and reverse transformation and the slicing with a conventional slicer. Despite the enormous development effort, certain problems could be handled more directly in this way. For example, the refinement of the triangles or the splitting of the straight lines would be  
Figure 24: Section of part with inward and outside overhang.  
omitted. The quality problems could also be solved more easily since the slicer would be optimized for the conical layers.  
Beside the work of [PERSON] [21], there is no other work known, where a similar slicing strategy was used or tested on an other machine than the 4-axis printer RotBot. At the moment there are no plans to test it on an other kinematics. The work of [PERSON] et al. [8] shows, that comparable approaches could be a feasible solution for other problems in the field of 3 Dp.  
Since professional FDM printers often work with soluble supports, the presented slicing and printing approach could therefore mainly be interesting for the group of printers, using the same material for the part and the support structure. If the remaining challenges can be solved, the outcome will be a enormous reduction of support material. However, there are major difficulties, like the automated splitting up of complicated parts, which must be solved to advance the whole process.