- 2021/04/09: spherical slicing redone, slightly better than before
- 2021/04/03: cylindrical & spherical slices added
- 2021/03/26: refocusing to non-planar slicing with planar slicing
- 2021/03/14: starting write-up with basic illustrations
After discovering the 4-axis Rotating Tilted Nozzle (RTN) and its prototype of RotBot as developed by ZHAW and their conic slicing method, it became clear to me a 5-axis 3D printer with variable tilting nozzle is the way to go as it is a superset of 4-axis and 3-axis 3D printing.
With that in mind, I realized there was time to explore non-planar slicing with planar slicers in more details.
Let’s provide an overview of various slicing methods:
Vertical slicing creates horizontal slices, the traditional aka planar slicing method, so issues and limitations are well known:
- simple to slice
- only challenge is to create support structure for overhangs to ensure all printed layers have layers beneath
- no collision detection needed, as all already printed layers are beneath
Tilted slices are kind of new(er) and became known with belt printers, usually 45° tilted:
Transformation is [ x, y, z – y ]
- simple to slice
- belt-printer: no collision detection is needed
- can print 90° overhangs in one direction only
There are patches for Cura available to slice for belt printer, additional the experimental Slicer4RTN also provides tilted slicing.
- requires a center of the conic layers
- can print 90° overhangs, two distinct modes: inside out (outside cone), or outside in (inside cone) depending on direction to a central slicing cone center
- requires rotating and tilted nozzle aka Rotating Tilted Nozzle (RTN)
- angle of conic slicing can be changed from 45° to 20° and models become printable with vertical nozzle with reduced print quality
Transformation is [ x, y, z + sqrt( x2 + y2) ]
I implemented a conic slicer named Slicer4RTN in 2021/03. There are more complex conic transformations possible, e.g. map the x/y angle via atan(y/x) but just adding sqrt(x2 + y2) to z does achieve a conic slice.
Early tests using planar slicers to slice also cylindrical, like this:
Transformation is [ atan(y/x), z, sqrt(x2 + y2) ]
It can be printed on a fixed vertical rod, with a rotating and tilting nozzle, or horizontal rotating rod (like a lathe) and vertical nozzle then:
I came up with this way by myself based on the study on conic(al) slicing but I was made aware researchers Coupek, Friedrich, Battran, Riedel back in 2018 published a paper on this method already.
Early tests using planar slicers to slice also spherical, like this:
Transformation is [ sqrt(x2 + y2 + z2), atan(y/x), atan(z/sqrt(x2 + y2)) ]
It can be printed with a 5-axis like PAX printhead, it’s main advantage is to getting close to print continuous overhangs of any angle.
I suspect at least one more suitable and simpler sphere transformation, as soon I came up with such I add it on this blog-post.
It is possible to slice non-planar with planar slicers by mapping to and from the space of the slicing you like to have; yet in the slicing procedure some margins are introduced which need to be compensated – the planar slicer needs to work reliable, Slic3r 1.2.9 and CuraEngine 4.4.1 / cura-slicer perform reliable, whereas PrusaSlicer 2.1.1 makes assumptions of the printability and exits when no printable G-code can be produced, not recommended for this case therefore.
The simpler the transformation forward and backward, the more precise G-code can be obtained, e.g. tilted and conic slices provide precise G-code, whereas cylindrical and spherical slices are harder to tune with the planar slicer.
- Conic Slicing for Rotating Tilted Nozzle (RTN)
- Multi-Axis Printing & Overhangs
- Cylinder Slicing: [Coupek, Friedrich, Battran, Riedel] Reduction of support structures and building time by optimized path planning algorithms in multi-axis additive manufacturing (2018) – free PDF
- Conic Slicing: [Wuethrich, Elspass, Bos, Holdener] Novel 4-axis 3D printing process to print overhangs without support material (2020) – non-free PDF, does not reveal actual transformation for conic slicing; future paper in 2021 will explain conic slicing though