A few basic examples combining planar and non-planar slicing methods on sub-volume segmented models illustrating the possibilities printing without support structures:
Fused Deposition Modeling (FDM) also known as Fused Filament Fabrication (FFF)
Using non-rotating but tilted sliced (like used with belt-printers) but in two distinct directions:
3 segments: z-planar & 2x tilted
starting z-planar
finishing z-planar
starting 2nd segment with tilted slices into one direction
2nd segment tilted continuing
2nd segment tilted finishing
3rd segment tilted into other direction
extending 3rd segment further
finished piece
T-model segmented into 2 sub-volumes, sliced z-planar and twice tilted in opposite directions
Tilted slices can be printed with 4-axis Rotating Tilted Nozzle (RTN) but the first Z-planar part, as mentioned above, might not provide sufficient surface quality, whereas a 5-axis Penta Axis (PAX) printhead can print both segments easily.
T-Model: 3 Segments: Z-planar & 2x X-planar
A more classic planar approach but with different planes as reference, first Z-planar then twice X-planar in different directions:
3 segments: z-planar, 2x x-planar
building up 1st segment z-planar
finishing z-planar segment
switching to 2nd segment, x-planar
extending x-planar
finish 2nd segment x-planar
switching other side x-planar opposite direction, 3rd segment
extending 3rd segment x-planar
finished piece
T-model segmented into 3 sub-volumes, sliced z-planar and twice x-planar
X-planar printing requires either 5-axis Penta Axis (PAX) printhead or the ability to tilt the bed.
Overhang In/Out: 2 Segments: 2x Conic
Lower part is sliced with conic slicing with inside-cone mode to print in-going overhang, whereas the upper part is sliced with outside-cone mode to cover the out-going overhang:
bottom: inside-cone, top: outside-cone
inside cone mode for 1st segment
inside cone mode
inside cone mode actual inner overhang
finishing inner overhang
switching to outside cone mode
building up 2nd segment
outside cone mode actual outer overhang
extending outer overhang
finished piece
Overhang in/out model segmented into 2 sub-volumes: lower part is sliced conic (inside-cone mode) and upper part conic (outside-cone mode)
Another overhang piece, stretching out into one direction; the lower part Z-planar, and the overhang conic (outside-cone mode) with an offset to align better with the lower segment:
2 segments: planar (bottom), conic with center offset (top)
after z-planar switching to conic (outside cone), conic center align with lower segment
conic part reaching edge of lower segment
full height of overhang segment
extending the overhang further
conic part asymmetrically extending
conic parts reached all horizontal model limits
finishing up the segment
finished piece
Overhang Out No 5 model segmented into 2 sub-volumes: z-planar at the bottom and overhang segment conic (outside-cone mode)
Overhang Out No 5: 3 Segments: 2x Z-planar & Conic
Perhaps a more realistic approach using the conic part as a “balcony” just for the overhang part sufficiently thick to carry next segment and switching back to Z-planar:
3 segments: planar (bottom), conic (middle) and planar (top)
z-planar segment
changing to conic segment
building up the conic overhang segment
actual overhang with conic slices
reaching out the 2mm thick segment
finishing the 2mm thick conic segment
and continuing with z-planar segment
finished piece
Overhang Out No 5 model segmented into 3 sub-volumes: z-planar first, then conic (outside-cone) building a thin “balcony” as support for the z-planar part on top again
Early tests have shown the thickness of the conic overhang “balcony” depends on the actual length of the in-air overhang, where print speed, part-cooling capacity and extrusion consistency determine the geometrical accuracy. More examples with “balcony” printed with 3-axis FDM printer followed.
Conclusion
Unlike with ordinary Z-planar slicing, it may be suitable to dedicate a particular slicing method and orientation for sub-volumes in order to take advantage of the possibilities like avoiding support structure, particular strength properties or surface quality.
solely z-planar sliced, support structure required using 3-axis FDM printer
sub-volume segmented, z-planar and conic sliced printable without support structure using 5-axis FDM printer
This of course opens a wide-range of possibilities and complexity therefore:
but I think it’s worth it, in particular when a piece is printed more than once like with small series manufacturing / production.
The examples have been produced with various slicers and combined with a new application coordinating the segmenting and dedicated slicing methods, which currently (2021/04) is in development; it also involves a new file-format describing the segmenting and its slicing settings. The segment positioning was done manually as a start, but I expect with more experience and research some cases can be detected automatically.
Sub-volume segmenting is just one approach to take advantage of 5-axis FDM printing, another is continuous slicing along the form.
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
angle of conic slicing can be changed from 45° to 20° and models become printable with vertical nozzle with reduced print quality
20mm cube
conic mapped
conic mapped sliced
20mm cube conic sliced
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.
Cylindrical Slices
Early tests using planar slicers to slice also cylindrical, like this:
20mm cube
cylinderical mapped
cylinderical mapped planar sliced
cylindrical radius corrected mapped
cylindrical radius corrected planar sliced
20mm cube cylindrical sliced
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.
(Hemi-)Spherical Slices
Early tests using planar slicers to slice also spherical, like this:
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.
Conclusion
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, Slic3r1.2.9 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.
2021/05/01: 0.0.7: support legacy Cura and --binary=.. to change binary name
2021/03/24: 0.0.5: public release
Introduction
I’m a great admirer of the Ultimaker Cura slicer since years, yet I predominantly have been using CuraEngine on the command-line via Print3r, which hides all the tedious configuration. But it came the point (2021/03) when I needed to have a simpler interface than CuraEngine – hence I wrote Cura CLI Wrapper, the executable cura-slicer looks like prusa-slicer or slic3r and has similar usage.
Speciality is to query all the settings from cura-slicer directly:
which lists ~570 settings as of CuraEngine 4.4.1 and its defaults and from where the defaults come from (definition defaults, config or cli), and you can query also a term e.g. like ‘brim’:
and with -v switch you even get a more descriptive output:
% cura-slicer --help brim -v
== acceleration_skirt_brim (Skirt/Brim Acceleration) ==
The acceleration with which the skirt and brim are printed. Normally this is done with the initial layer acceleration, but sometimes you might want to print the skirt or brim at a different acceleration.
acceleration_skirt_brim = 3000 [mm/s²] (default)
== brim_gap (Brim Distance) ==
The horizontal distance between the first brim line and the outline of the first layer of the print. A small gap can make the brim easier to remove while still providing the thermal benefits.
brim_gap = 0 [mm] (default)
== brim_line_count (Brim Line Count) ==
The number of lines used for a brim. More brim lines enhance adhesion to the build plate, but also reduces the effective print area.
brim_line_count = 0 (config)
== brim_outside_only (Brim Only on Outside) ==
Only print the brim on the outside of the model. This reduces the amount of brim you need to remove afterwards, while it doesn't reduce the bed adhesion that much.
brim_outside_only = 1 (default)
....
Essentially it makes Cura and CuraEngine easy to use on the command-line and provides a way to learn of the hundreds of settings available.
Usage
USAGE Cura-Slicer 0.0.7 aka Cura-CLI-Wrapper (CuraEngine 4.4.1): [<opts>] <file.stl> ...
options:
-v or --verbose increase verbosity
-vv or --verbose=2 " "
--version display version of this program and exit
--load=<config> load config file
--load <config> " "
--output=<fn> set output filename
--output <fn> " "
-o <fn> " "
--binary=<exe> set executable of CuraEngine (default: CuraEngine)
--version=<v> set version of CuraEngine (default: 4)
--<k>=<v> set CuraEngine settings (keys with '-' will be converted to '_')
-h or --help display all settings
-h or --help <term> .. display settings matching term
examples:
cura-slicer --help
cura-slicer --help retract
cura-slicer -hv retract
cura-slicer sphere.stl
cura-slicer overhang.stl --output=sample.gcode
cura-slicer overhang.stl --layer-height=0.1 --support-enable=true -o sample.gcode
Settings
The user settings reside in ~/.config/cura-slicer/base.ini and will not be overwritten when upgrading Cura-CLI-Wrapper, make your changes there.
The system-wide settings reside in /usr/share/cura-slicer/base.ini and should not be be changed as it will be overwritten when upgrading Cura-CLI-Wrapper.
2021/03/22: 0.4.5: source released on github, page published
2021/03/20: 0.4.2: adding more core slicer examples
2021/03/17: 0.3.1: start writing page, provide overview of settings
Introduction
Slicer4RTN aka “Slicer for Rotating Tilted Nozzle (RTN)” is a highly experimental conic slicer utilizing existing planar slicer like Slic3r with pre- and post-processing to create G-code which can be printed with a 4-axis RTN, allowing to print particular overhangs without support:
printing 90° – 110° overhangs without support, given some conditions
unidirectional tilted slicing (tilted nozzle)
variable tilt angle
printing 90° – 110° overhangs in one direction, like possible with a belt printer
And yes you can print non-planar conic sliced G-code with an ordinary 3-axis 3D printer if you dare, something like this:
Just keep your expectation on the print quality low, as you try to print with a vertical nozzle which is meant to be printed with a tilted nozzle, but you will be able to print 90° overhangs without support structure.
% slicer4rtn
USAGE Slicer4RTN 0.4.4: [<opts>] <file.stl> ...
options:
-v or --verbose increase verbosity
--version display version and exit
-k or --keep keep all temporary files (temp.stl, temp.gcode)
--recenter recenter model X- & Y-wise
--subdivide=<n> set midpoint subdivisions (default: 2)
--mode=<mode> set cone mode, either 'outside' or 'inside' (default: 'outside')
--output=<fname> override default naming convention file.stl -> file.gcode
--axis=<axis> set axis count of printer: 3, 4 or 5 (default: 4)
--angle=<angle> set angle of cone (default: 45)
--center=<cx,cy> set conic slicing center (default: 0,0)
--bed-center=<cx,cy> set bed-enter, only affects output G-code (default: 100,100)
--layer-height=<z> set conic layer height (default: 0.2)
--rot-gcode=<v> set G-code symbol for rotation (default: A)
--rot-revolv=<mode> set rotation revolution, 0 = unlimited, 1 = once (default: 1)
--rot-offset=<a> set rotation offset (default: -90)
--rot-fixed=<angle> set fixed rotation angle, usable if --axis=3 but 4-axis or 5-axis printer is target
--tilt-gcode=<v> set G-code symbol for tilt for 5-axis operation (default: B)
--zoff=<v> set z-offset, will be added to G1 ... Z<v>
--erate=<f> set extrusion rate (multiplier, default: 1)
--efmin=<v> set extrusion factor minimum, (default: 0.01)
--efmax=<v> set extrusion factor maximum, (default: 3)
--inter-steps=<n> set interpolation steps per mm (default: 2)
--motion-minz=<v> set minimum Z level for motion (without extrusion) (default: 0.2)
--max-speed=<s> set maximum speed (default: 0)
--slicer=<slicer> set slicer (default: 'slic3r')
--slicer.<k>=<v> add additional slicer arguments, e.g. --slicer.infill-density=0
--<k>=<v> all other arguments not for slicer4rtn will be passed to the core slicer (slic3r)
examples:
slicer4rtn sphere.stl
slicer4rtn overhang.stl --output=sample.gcode
slicer4rtn overhang.stl --axis=5 --output=sample.gcode
slicer4rtn overhang.stl --axis=3 --output=sample-belt-printer.gcode --fill-density=5
slicer4rtn model-6.stl --angle=25 --subdivide=5
Options
subdivide
By default the faces of model is 2x subdivided, you can turn it off by --subdivide=0 or increase like --subdivide=5 for a cube. The current algorithm depends on sufficient detailed faces.
original STL
subdivide=0
subdivide=1
subdivide=2
subdivide=3
subdivide=4
subdivide=5
So for simple STLs choose subdivide=5 or higher, for already complex STLs with thousands of faces, you may go with the default.
recenter
If you slice a model you did not create yourself, very likely the model might not be properly aligned or centered, with --recenter you can enforce recentering the model X- and Y-wise.
mode
By default outside mode is used, you may change it with --mode=inside which slices for inside-cone printing. Currently slicer4rtn does not segment parts according their required mode, you have to do this manually right now. This may change with a later version.
mode=outside for outside overhangs
mode=inside for inside overhangs
Volume segmenting (not yet implemented): inside overhang printed in inside-cone mode, and outside overhang printed in outside-code mode
Needless to say, this mode switch is very basic and only makes sense for very simple models.
axis
By default G-code for 4-axis Rotating Tilted Nozzle (RTN) is generated (--axis=4), which includes rotational information.
--axis=3 generates tilted slices at angle 45° (which can be changed with --angle=..) which means overhangs can only be printed in one direction; the G-code can be printed with a 3-axis 3D printer now like a belt-printer; also --rot-fixed=.. one controls the direction of the tilt slicing
--axis=4 is the default, a 45° tilted nozzle is implied
--axis=5 adds an additional fixed tilt into the G-code like B45 and is printable on a 5-axis Penta Axis (PAX) printer
--axis=3
--axis=4 for RTN
--axis=5 for PAX
angle
By default the conic angle is set to 45° and can be changed with --angle=.., e.g. for a 3-axis 3D printer the angle can be set to 15..25° to print conic slices with a vertical nozzle.
angle=45 (default)
angle=30
angle=20
20mm cube conic sliced at 45°, printed with rotating 45° tilted nozzle (animated)
20mm cube conic sliced at 20°, printed with vertical nozzle (animated)
By default the conic slicing center is set to 0,0 and can be change with --center=x,y
20mm cube, center=0,0
center=0,0 (50% complete)
center=5,0 (50% complete)
center=10,0 (50% complete)
You control the conic slicing center twofold:
with the model itself
with --center=cx,cy
You may use --recenter switch to force the model be recentered X- & Y-wise; this is recommended if you did not create the model yourself and the STL is not centered properly.
bed-center
The slicer final output will be offsetted by these coordinates, by default it is 100,100 which should work for most 3D printers.
layer-height
By default 0.2mm conic layer height is set, and can be changed with --layer-height=h [mm]
Note: the layer height for the core slicer is calculated and might exceed the hard limits of the core slicer, so reduce the layer height so that slicer4rtn doesn’t stumble.
rot-gcode
By default the rotational angle is passed to G-code with A and can be changed, e.g. the RotBot uses U in the firmware to process the rotation angle, hence using --rot-gcode=U
rot-revolv
By default the printhead can only revolve once (-180°..180°), hence --rot-revolv=1; a more mechanical complex RTN is the RotBot by ZHAW which permits unlimited rotations with a slip ring, then use --rot-revolv=0
rot-revolv=1
rot-revolv=0 (unlimited)
Note: rot-revolv=0 resets at layer change the rotation angle to mod(360) again.
rot-offset
The rotation angle of the tilted nozzle is calculated by the traditional X/Y coordinate system; as I designed my Rotating Tilted Nozzle (RTN) I defined the 0° to be in front, and traditional counter-clockwise with increasing angle; so by default rot-offset is equal -90°.
20mm cube conic sliced, printed with 4/5-axis nozzle, rot-offset=-90 rotation angle A, and tilt angle B shown
rot-fixed
In case you like to have non-rotating printing and single direction slicing therefore, then fix the angle with --rot-fixed=angle.
20mm cube 50% printed with axis=3
20mm cube 50% printed with axis=3 rot-fixed=90
20mm cube 50% printed with axis=3 rot-fixed=-45
tilt-gcode
In case when targeting 5-axis Penta Axis (PAX)--axis=5 the tilt G-code is added as default as Bangle, you may change the code with --tilt-gcode=V for example.
erate
In case you have trouble with under- or over-extrusion you can change the multiplier with --erate=f for example to reduce extrusion by 10% use --erate=0.9
inter-steps
By default 2 steps per mm are interpolated per planar G1 extrusion, you may refine it by increasing it, e.g. --inter-steps=4; be aware it creates larger G-code outputs.
slicer
By default Slic3r (slic3r) is used as core slicer, an overview of current supported core slicers, selectable with --slicer=...
Slic3r 1.2.9 (slic3r): gives good results so far with minimal configuration ★★★★★
Prusa Slicer 2.1.1 (prusa-slicer): struggles to slice inverted conic models and fails to create G-code with a message like Empty layers detected, the output would not be printable. It may help to increase --subdivide=n, be aware of immense amount of faces ★★★★★
Mandoline (mandoline): fails mostly to slice inverted conic models, but could become relevant in later development ★★★★★
CuraEngineLegacy 15.10 (CuraEngineLegacy): outdated but surprisingly gives good results, easy to use on command-line ★★★★★
CuraEngine 4.4.1 (CuraEngine): gives good results, but is tedious to configure on command-line as requires base configuration in .json, which changes with each new version; it gives warnings & errors for small polygons but makes an effort regardless giving G-code (good behavior, better than Prusa Slicer) ★★★★★
Cura CLI Wrapper (cura-slicer): same as CuraEngine but easier to configure (allows to query hundreds of possible settings directly with cura-slicer (recommended)
Step 1: Original
Step 2: Inverse Conic Mapped
Step 3: Sliced Normally
Step 4: G-code Conic Mapped
Example of 20mm cube & overhang nr 3 4mm shown at 50% complete:
Slic3r 1.2.9 with fill-pattern=rectilinear
Prusa Slicer 2.1.1
CuraEngine 4.4.1
CuraEngineLegacy 15.10
Slci3r 1.2.9
Prusa Slicer 2.1.1
Cura 4.4.1
CuraEngineLegacy 15.10
Slic3r 1.2.9 performs reliable on 20mm cube and overhang nr 3 4mm model, and CuraEngine 4.4.1 gives excellent results as long layer-height is low (below 0.2), whereas older Cura 3.8.x struggles – so definitely use Cura 4.x series.
G-code Size
As conic slices range over X, Y and Z, the G-code becomes quite verbose compared to horizontal slices, for example20mm cube sliced both times with Slic3r 1.2.1:
horizontal slices: 152 KiB (4.7K G1 lines)
conic slices: 7,565 KiB (93.6K G1 lines)
which is a significant increase of 50x size of G-code and 20x more G1 statements.
Common Settings
By default
/usr/share/slicer4rtn/slicer4rtn.ini (system-wide) and
~/.config/slicer4rtn/slicer4rtn.ini (user)
are considered where all settings can be listed to provide new defaults for slicer4rtn, for example:
# my own settings:
layer-height = 0.15
bed-center = 120,100
rot-offset = 0
rot-resolv = 0
You can use ‘#‘ as a leading indication that the rest of the line is a comment and disregarded.
Note: It is recommended to only list slicer4rtn specific settings there, not slicer specific settings (see below).
Slicer Specific Settings
Each core slicer may have their own base settings, so you don’t need to add it everytime when calling slicer4rtn, so include them in your user settings:
User Slicer Settings
~/.config/slicer4rtn/slic3r.ini
~/.config/slicer4rtn/prusa-slicer.ini
~/.config/slicer4rtn/mandoline.ini
~/.config/slicer4rtn/CuraEngine.ini
~/.config/slicer4rtn/CuraEngineLegacy.ini
~/.config/slicer4rtn/cura-slicer.ini
Make your changes in those files, as they will not be overwritten when you upgrade slicer4rtn in the future, for example slic3r.ini:
external-perimeter-speed = 10%
Note: slic3r and prusa-slicer directly load their slicer specific settings from the file, whereas the other slicers the settings will be parsed by slicer4rtn and passed on via internal command-line execution.
System-Wide Slicer Settings
By default make install installs some base system-wide configs in /usr/share/slicer4rtn with the same filenames as mentioned above, those will be overwritten in future releases of Slicer4RTN, but your user settings will not be overwritten.
When running slicer4rtn is executed first are the system-wide configs loaded, then the user specifics.
Print3r & Slicer4RTN
As of print3r 0.3.2 or later slicer4rtn is supported as well:
.config/print3r/printer/<yourprinter>.ini and make a copy like .config/print3r/printer/<yourprinter>-rtn.ini add following lines:
slicer = slicer4rtn
# slicer4rtn specific seeting prepend 'slicer4rtn.' for settings, like:
# slicer4rtn.slicer = prusa-slicer
angle = 25
and alter the start-gcode line with increasing Z motion as well, e.g for my Prusa-i3 clone it has a M6 threaded rod, which means one revolution (200 full steps) 1mm Z motion, hence
start-gcode = ".....\nM203 Z6\n...."
increased Z motion speed to come close to X- and Y- speed, it creates more even extrusions, nicer prints.
Actual use with print3r goes then like this, my Prusa-i3 clone named y3228-rtn now:
it slices and forwards the G-code according your setup without the requirement to invoke slicer4rtn manually anymore.
References
RotBot by ZHAW, the inventors of the Rotating Tilted Nozzle (RTN) approach by Prof. Dr. Wilfried Elspass, Dr. Christian Jaeger, Michael Wüthrich, Maurus Gubser, Philip Bos and Simon Holdener
2021/03/11: starting write-up with basic illustration
Introduction
I thought to compose a summary of the features of 3 types of 3D printers I currently work on, and its relations to print 90° overhangs – main motivation to go beyond 3-axis 3D printing:
Functionality Commonalities
a 5-axis printer PAXhas the same features as a 4-axis printer RTN and 3-axis printer plus it can print at any tilt angle, printing 90° or more overhangs
a 4-axis printer RTN prints conic- or angled sliced models so it can print 90° overhangs in all directions (conic slice) from a central point or single direction (angled slice); the tilt angle is fixed at 45°; Z sliced horizontal layers must be post-processed1) to be printable in good quality
a 3-axis printer by default cannot print 90° overhangs without support (unless it’s tilted 45° as for belt-printer, then only in one direction), but may printconic sliced models with 20-25° cone angle, henceprint 90° overhangs from a central point, and behave partially like a 4-axis printer
a suitable Zrot must be calculated and added to extrusion commands of the G-code, see this example.
Printing an Conic Sliced Overhang
Conic sliced, in this case 45° conic angle, model nr 6 (table-like), with 45° tilted nozzle (simulation, animation)
Conic Sliced on 3-axis
3-axis vertical nozzle printing 25° cone sliced model: overhangs in all directions without support
3-axis with vertical nozzle
3-axis with vertical nozzle
A well tuned and well designed part-cooler is prerequisite to print conic-sliced models at cone angle of 20-25°, and currently there is no conic slicer which can properly segment sub-volumes yet (2021/03) to switch from horizontal- and conic-slicing (with two modes of outside/inside cone) where suitable.
Conic Sliced on 4-axis RTN
4-axis RTN printing 45° cone sliced model: overhangs in all directions without support
4-axis RTN printing 45° cone sliced model: overhangs in all directions without support
4-axis RTN printing 45° cone sliced model: overhangs in all directions without support
5-axis PAX printing 45° cone sliced model: overhangs in all directions without support
5-axis PAX printing 45° cone sliced model: overhangs in all directions without support
5-axis PAX printing 45° cone sliced model: overhangs in all directions without support
and nearly the same with PAX90 (tilt angle 0..90° only) with shorter arm:
5-axis PAX90 setup
5-axis PAX90 printing 45° cone sliced model
5-axis PAX90 printing 45° cone sliced model
A 5-axis Penta Axis (PAX) supports other slice methods than horizontal-, angled- or conic-sliced, but any variable build-orientation, but will make the slicing software very complex to recognize those sub-volumes suitable for advanced slicing methods.
This also means, a 5-axis PAX slicer with proper settings can produce G-code for 5-, 4- and 3-axis 3D printers with combining the horizontal-, angled- and cone slicing for sub-volumes or segments.
Traditionally Horizontal Layers
Slic3r 1.2.9 and Ultimaker Cura 4.8 as comparison:
Slic3r 1.2.9 G-code (viewed in Cura)
Cura 4.8 G-code
Cura G-code, underside
Cura adds support structure, apprx. 30% of material just for support
2021/03/19: some information on use of slicer4rtn (not yet released)
2021/03/09: removed lengthy “Test Protocol” and extended “Gallery” section a bit
2021/03/08: slicer4rtn at 0.2.4 (still unreleased) resulting in better prints, blog-post linked at hackaday
2021/03/05: 95° and 100° overhangs are printable too, more bug-fixes in slicer4rtn
2021/03/04: fixing various bugs in slicer4rtn as disovered printing more complex pieces, supporting prusa-slicer as well aside slic3r, pushing the limits with overhangs
2021/03/02: documenting my findings, a few photos, some early conclusions (not even one day old), conic sliced and tilt sliced.
90° Overhangs without support structure on 3-axis 3D printer
Introduction
It has been target of many efforts to print 90° overhangs without support on 3-axis 3D printers as with ordinary Z slicing, each layer requires a support underneath; hence, every overhang then needs a support structure if the model itself doesn’t provide it.
While reflecting on the output of the 4-axis conic sliced models, I thought what if I simply make the cone angle flatter than 45° but 15-25° so the vertical nozzle can print it?
Overhang model conic sliced at 25° angleslicer4rtn --angle=22.5 sliced overhang model, meant for 4-axis printer, but printed on 3-axis printer
Conic Slices Simulation
A simple overhang model (nr 3) conic sliced at 25° for 0.4mm nozzle, 0.2mm layer height:
Tilted Slices Simulation
The same overhang model (nr 3) tilt sliced at 25° for 0.4mm nozzle, 0.2mm layer height (like with belt printer):
Conic Slices Print Tests
And on the afternoon of March 1st 2021 I ran my G-code for the first time on an ordinary 3-axis printer, a cheap CTC DIY I3 Pro B (Prusa-i3 like), in the attempt to print 90° overhangs, with a conic sliced overhang model:
Wow – it seems to have worked! There were still some issues, like the nozzle without extrusion moved into the print as I forgot map linear motions without extrusion also to conic coordinates as well, and some other minor things.
You may consider this a “backport” of 4-axis slicing procedure back to a 3-axis 3D printing procedure.
Next Day Attempts
Conic Slices
The print is still pretty ugly due to the obvious under-extrusion, but the geometry seems to work overall. The overhang on the left-front isn’t evenly, as the outer wall print speed is still too high.
Tilted Slices
heatblock comes awfully close
Very clean print so far but the overhang is limited to one direction (see below of overall considerations).
Findings
Well,it works, but here are some limitations of using non-planar slicing:
more complex pieces need to be volume decomposed or segmented, e.g. some sub-volume sliced ordinary vertically Z-wise, others conic sliced where needed – this is part of my research on 4-axis and 5-axis printers; and I was hoping some of the findings can be applied to 3-axis 3D printer as well (as this post shows)
the printhead geometry with heatblock sock, part-cooler, LED light they quickly come into way with larger pieces and larger overhangs
this might look minor, but part coolers play significant role for quality prints, so they need to be optimized for non-planar printing
cone angle
15° works, sufficient space around the nozzle, but on the edge for overhangs, better surface quality
20° works better, layers more stable beneath the overhang
25° works too, but is the limit on my E3D V6 clone, poorer surface quality, but overhang prints better
print quality is sub-optiomal, as the nozzle runs over its own extruded filament and any “flat” surface becomes jittery as it’s not longer flat (toward Z) printed
Tilted Slices
single direction angled slice like with belt-printer
only one direction overhang possible, but good quality
tilt angle:
25° works good, yet, the heatblock comes into the way rather quickly with my sample overhang model
Conic vs Tilted Slices
25° conic sliced overhang model
25° tilt sliced overhang model
Issues to Resolve
more tests
more beautiful prints
fine tune extrusion rate: the current slicer4rtn does a simple/poor interpolation causing rough top surfaces (under- vs overextrusion)
fine tune outer wall of overhangs, slow them down
--slicer.external-perimeter-speed=10% (Slic3r)
support more slicers
Slic3r: supported since slicer4rtn 0.0.1
Prusa Slicer: supported since slicer4rtn 0.1.2 (0.1.1 was broken) but often refuses to slice model, e.g. cube fails in inverted cone space
Trying out an overhang model which extends -Y and Y (as side-ways the part-cooler comes into the way)
There are still inconsistencies with extrusion calculation, but the prints getting cleaner.
4-sided overhang model nr 6 (conic sliced)
Sample print comes soon as I need to redesign my part cooler so I can print this piece.
1-sided long 4mm thick overhang model nr 3 (conic sliced)
Long 40mm overhang, just 4mm thick extending nose . . .
a bit rough
a few layers definitely hang, overextrusion or lack of proper cooling
right front is missing some material, rough top of the foot at the back
X-wise OK
1-sided long 2mm thick overhang model nr 3 (conic sliced)
Long 40mm overhang, just 2mm thin extending nose, let’s push the limits of what’s possible:
good
still good
still good?
going good further
wow, it keeps staying good
the final bends a bit upward
last layers in front are OK but one sees the limit here
X-wise very good, surface of the foot is still rough
OK print so far, better than anticipated, but still a way to improve it. Reprint with a newer version of slicer4rtn (0.2.3):
in print
finished, bowed up, but thickness and print quality improved
surface is clean(er), smooth
underside is uneven, too fast printed (20mm/s)
better surface, no stringing anymore
faster print speed but also more geometric inconsistency like bending up
underside is more uneven but also cleaner than all the previous (pre- 0.2.0 of slicer4rtn)
1-sided short 2mm thick 95° overhang model nr 3 (conic sliced)
Just trying more overhang, let’s see.
good so far
looks good 95° overhang
still rough surface
Obviously there is more than 95° overhang possible, so let’s try …
1-sided short 2mm thick 100° overhang model nr 3 (conic sliced)
Even steeper overhang, let’s see.
it’s actually seems to still work
a bit rough at the beginning of the overhang
good so far
can’t believe this works
just wow, 100° overhang
rough surface
This is truly promising, up to 100° overhangs printable with vertical nozzle as mounted on most 3-axis 3D printers . . .
95° overhang
100° overhang
Slicer4RTN Settings
As of the publication of this blog-post (2021/03) no slicer is available but slicer4rtnwill be made available soon which was released 2021/03/22.
Caution: you need to be an experienced 3D printing enthusiast to proceed, you need to know and realize what you do:
pay close attention of the printhead geometry, such as the nozzle and heatblock, and the part cooler which limits the non-planar printing
depending on the angle, and the direction of extrusion more or less extrusion distortion will occur
Issues to look at when printing conic sliced models with vertical nozzle on a 3-axis 3D printer
--angle=20 is a good start, you may go as low as 15°, and perhaps at max at 30° depending on your nozzle and heatblock, if you aim to print 90° overhangs
--layer-height=0.2 is a good start too, the thinner the layers the better overhangs can be printed
if you have trouble with over- or under-extrusion and your printer otherwise well tuned, then use --erate=f as extrusion-rate tuning, whereas f = 0.5..1.5 or so, if you have to go below or above, something else is wrong.
conic slicing is complex(er), you need to think in new terms:
the slicing procedure requires a conic slicing center
to and from that center overhangs can be printed well
if you have multiple centers, slicer4rtn does not yet support volume segmenting to support multiple centers
slicer4rtn requires manually entered conic slicing center
it requires fine-grained faces so the slicing works well, use --subdivide=5 or higher for simple pieces, e.g. like a cube or low-poly models in generals
Tuning 3-axis 3D Printer
Following changes are recommended:
increase Z axis speed: within the start G-code the line M203 Z.. (replace .. with an actual number) to increase speed of Z-axis
depending on the pitch of your Z-lead screw or threaded rods, you may set it to Z4, Z6, or higher, so the motion speed comes close to X- and Y-axis to improve print quality
if it’s set too high, your stepper motor will block and not move at all
my setup with M6 threaded rod for Z (200 full steps = 1mm):
State: early draft, mostly simulations with a few tests with 3-axis printer only
Conic sliced overhang model with two overhangs, printing with Rotating Tilted Nozzle (RTN) 90° overhang structure without support structure
Updates:
2021/03/22: slicer4rtn released, see dedicated page Slicer4RTN
2021/03/16: removing details on slicer4rtn as a new dedicated page is in the working (coming soon)
2021/03/08: slicer4rtn 0.2.3 reached (still unreleased), better prints, documenting various settings in more details
2021/03/05: added proper ZHAW reference in the introduction and a few notes
2021/02/27: removed some redundant illustrations and remade some of them, outside-cone vs inside-cone mode & printing
2021/02/26: added inside-cone printing example for inner overhang mode, also early information of slicer4rtn; more animations to observe details of produced G-code, using now also OpenSCAD to simulate G-code and actual nozzle position
2021/02/24: better tests with 20mm cube and overhang structure, included two short G-code simulations as videos, added 20mm sphere and 3D Benchy and discover first issues with volume decomposition and overhang recognition
2021/02/23: first write up, pseudo code and first attempt to conic slice 20mm cube
As I progress I will update this blog-post.
Introduction
The main idea is to utilize existing 3D printing slicers but create conic slices for the Rotating Tilted Nozzle (RTN) 4 Axis Printer. ZHAW published in their announcement in 2021/01 something about utilizing existing slicers, but the details remained concealed and later published as a paper but I did not want to wait and pondered on the problem, and came up with a solution. In its current state it’s purely theoretical and untested for now (2021/02)barely tested yet.
Michael Wüthrich confirmed my solution is comparable with their solution. ZHAW planned their paper to be published sometime 2021. So, the main credit goes to ZHAW and the researchers (Prof. Dr. Wilfried Elspass, Dr. Christian Jaeger, Michael Wüthrich, Maurus Gubser, Philip Bos and Simon Holdener) there, I was just impatient and tried to find a solution with the information available.
The 4-axis Rotating Tilted Nozzle (RTN) physical setup implies its slices are of non-planar conic shape, allowing to print overhangs without support structure, such as:
Conic slices of an overhang model
I also like to master the conic slices properly as they promise to become a subset of 5 axis printhead (PAX) features too – so it’s worth the effort even if the RTN itself might be too limited in its application with its fixed tilt – we will see.
function conicSpaceMapping(cx,cy,x,y,z,dir='direct') {
dx = x-cx;
dy = y-cy;
d = sqrt(dx*dx + dy*dy);
rot = atan2(dy,dx);
return (x,y,dir=="direct" ? z-d : z+d,rot);
}
Pseudo-Code
The entire procedure goes like this:
m = loadModel("cube.stl");
m = subDivide(m,5);
for(p of m.vertices) {
m.vertices[i] = conicSpaceMapping(cx,cy,p.x,p.y,p.z,'inverse');
i++;
}
gcode = sliceModel(m);
foreach(line of gcode) {
(code,x,y,z,e) = extractCoordsExtrusion(line);
(x1,y1,z1,zrot) = conicSpaceMapping(cx,cy,x,y,z,'direct');
outputGcode(code,x1,y1,z1,e,zrot);
}
Note: the pseuco-code is incomplete as extrusion E is not yet taken care of, as soon I found a definitive solution I will write it up.
Examples
I implemented the pseudo-code with some more details like taking care of G-code E extrusion as well and fine-step linear extrusion – here some early tests using OpenSCAD as STL & G-code viewer and Slic3r as actual slicer:
find good pre-processing face sub-division strategy
in its current form the algorithm requires fine-grained sub-divided faces otherwise inaccurate G-code is created which cannot be recovered
3D Benchy conic sliced with Original Faces
3D Benchy conic sliced with Refined Faces
slice more complex parts
3D Benchy: requires more thorough examination, e.g. volume decomposition to segment roof apart:
Impossible printing: current conic slicing needs to recognize overhangs and apply volume decomposition to choose right strategies – otherwise new issues arise which in Z planar slicing do not exist
Same G-code position of the Inverse Conic sliced model: > 90° overhang created, and causes in-air structure – might require actual support structure (!!), volume decomposition required
document all details
release source code to public
Close-Ups
Some close-ups of conic sliced models:
20mm cube (partial)
3D Benchy (roof & chimney)
3D Benchy (cabin)
Overhang model (top view)
Overhang model (view on actual overhang)
Outside- vs Inside-Cone Printing
As pointed out in the previous blog-post, the RTN has two main modes of operation, outside-cone and inside-cone printing to cover outside overhangs and inside overhangs – the slicer must recognize those and switch operation mode. Further, these two modes cannot easily be mixed, and need to be segmented or separated, hence speaking of volume segmentation.
Outside Cone printing
Inside Cone printing
outer overhang
inner overhang
outside-cone printing for outside overhangs
inside-cone printing for inside overhangs
Inside cone for inner overhangs (bottom) vs outside cone for outside overhangs (top)
This poses significant grow of complexity from just planar slicing, the 4-axis RTN provides features to print 90° overhangs without support structure, but only when the part can be properly analysed and segmented so that those operational mode can be applied.
The difference between inside- and outside-cone printing is to change the order of conic mapping for the model and post slicing:
outside-cone mode
map model inverse conic
slice model
map G-code direct conic
inside-cone mode
map model direct conic
slice model
map G-code inverse conic, Zrot + 180°
Slicer4RTN
The pseudo-code turned into an actual application I named slicer4rtn and is a command-line tool, slicing STL into G-code:
I gonna released Slicer4RTNeventually 2021/03/22, in its early version the model currently can only be sliced for outside-cone or inside-cone printing, so the volume decomposition or segmentation needs to be done separately. For now it helps me to verify some of the 4-axis and 5-axis printer designs I work on.
Ashtar K RTN printing conic sliced 20mm cube (close up, animation)Ashtar K RTN printing conic sliced overhang model without support structure (close up, animation)Ashtar K RTN printing conic sliced overhang model nr 6 (table-like) without support structure (close up, animation)
RotBot by ZHAW, the inventors of the Rotating Tilted Nozzle (RTN) approach by Prof. Dr. Wilfried Elspass, Dr. Christian Jaeger, Michael Wüthrich, Maurus Gubser, Philip Bos and Simon Holdener
