Tag Archives: Non-Planar Slicing

3D Printing: Non-Planar “Balcony” Overhang with 3-axis FDM Printer

Updates:

  • 2021/05/02: adding overhang-inout with 5 segments, with conic inside- and outside-cone mode
  • 2021/05/01: adding tilt sliced overhang segment variant as comparison
  • 2021/04/29: video uploaded and blog-post published
  • 2021/04/27: first successful tests with vertical nozzle (3-axis FDM printer)

Introduction

The past few months and weeks I focused on the non-planar slicing, and the first tests with sub-volume segmenting and thereby mixing planar and non-planar sliced G-code worked as simulation, and now in actual prints.

One of the benchmarks are 90° overhangs in different directions, and I printed with vertical nozzle on an ordinary 3-axis FDM printer, therefore I prepared the G-code with a new tool (in-development) which coordinates segmenting and planar/non-planar slicing of sub-volumes, and the conic sliced segment was sliced with 25° conic angle so it remains printable with the vertical nozzle unlike the simulation where a 4- or 5-axis FDM printer is required:

Gallery

Conic Sliced Overhang Segment

The simulation as reference:

and the actual print process with vertical nozzle on a low-cost 3-axis FDM printer:

Excerpt of the actual printing process with brief annotations:

Tilt Sliced Overhang Segment

Just for sake trying out, instead of conic sliced overhang segment, tilt sliced and 45° Z rotated to nicely extend to the maximum overhang position:

and the actual print of a slightly lower model but with the same features:

Comparing Tilted Sliced vs Conic Sliced Overhang Underside

Overhang In/Out: 2 Overhang Conic Segments

5 segments (bottom to top): z-planar, conic (inside-cone), z-planar, conic (outside-cone), z-planar

And revisiting the Overhang In/Out Model, which features ingoing and outgoing overhang, segmented into 5 sub-volumes:

  1. bottom: z-planar
  2. ingoing1) overhang: conic (inside-cone mode)
  3. middle: z-planar
  4. outgoing1) overhang: conic (outside-code mode)
  5. upper: z-planar

1) when dealing with conic slicing, the direction of overhang matters when deciding the mode of conic slicing, e.g. outside-cone or inside-cone.


and the actual print, a half of the model so the printing of inner overhang on the lower part of the model is visible:

Conclusion

It took me a few days to tune the 3-axis FDM printer to print in acceptable quality of this Overhang Model No 5 and also Overhang In/Out Model. A strong part-cooler was mandatory, well adjusted print temperature and slow perimeter as those extrusions align horizontally without vertical support; and it worked: the main idea is to segment and limit the overhang part to ~2mm thickness – a quasi “balcony” – which still allows a classic vertical nozzle with part-cooler to print such, and then switch back to planar printing again.

Vertical nozzle with part-cooler printing conic sliced overhang – a “balcony” – working with narrow margins

Detail settings: the conic overhang was sliced with Slicer4RTN with following settings slicer4rtn --slicer=cura-slicer --speed_wall=10 --speed_wall_0=10 --speed_wall_x=10 ... and since the Z-axis motion is limited to 4mm/s (M6 threaded rod, 1 rotation => 1mm) the overall printing speed is slow enough to provide acceptable print quality.

References

3D Printing: Sub-Volume Segmenting & (Non-)Planar Slicing

Introduction

In order to take advantage of 4- and 5-axis non-planar FDM1) printing (e.g. tilted, conic, cylindrical, spherical) the model may be segmented and then dedicate slicing methods can be assigned to such sub-volumes.

A few basic examples combining planar and non-planar slicing methods on sub-volume segmented models illustrating the possibilities printing without support structures:

  1. Fused Deposition Modeling (FDM) also known as Fused Filament Fabrication (FFF)

T-Model: 2 Segments: Z-planar & Conic

Utilizing novel conic slicing as introduced by ZHAW researchers in 2020/2021:

T-model segmented into 2 sub-volumes, sliced z-planar and conic (outside-cone mode)

Conic slices can be printed with 4-axis Rotating Tilted Nozzle (RTN) although printing the Z-planar sliced part might not give goods surface results but rather using a 5-axis Penta Axis (PAX) printhead to cover both cases easily.

T-Model: 3 Segments: Z-planar & 2x Tilted

Using non-rotating but tilted sliced (like used with belt-printers) but in two distinct directions:

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:

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:

Overhang in/out model segmented into 2 sub-volumes: lower part is sliced conic (inside-cone mode) and upper part conic (outside-cone mode)

This model covers the classic case of 4-axis Rotating Tilted Nozzle (RTN) application: rotating 45° tilted nozzle printing in two different modes (outside-cone and inside-cone); a 5-axis Penta Axis (PAX) printhead also can print such.

Overhang Out No 5: 2 Segments: Z-planar & Conic

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:

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:

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.

This of course opens a wide-range of possibilities and complexity therefore:

  • where to segment
  • which slicing method to use
  • in which orientation the slicing is performed

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.

References

See Also

PS: All animations I combined in a short 3min video: Mixing Planar & Non-Planar Slicing Methods for 3D Printing Overhangs without Support Structure (YouTube)

3D Printing: Non-Planar Slicing with Planar Slicer

Updates:

  • 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

Introduction

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.

Slicing Methods

Let’s provide an overview of various slicing methods:

Horizontal Slices

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

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.

Conical Slices

New slicing method as introduced by ZHAW researchers and announced in 2021/01 utilizing planar slicer:

  • 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.

Cylindrical Slices

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.

(Hemi-)Spherical Slices

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.

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, 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.

References

3D Printing: Multi-Axis Printing & Overhangs

Updates:

  • 2021/03/14: more detailed references, published
  • 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 PAX has 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 acceptable quality but good quality cannot be achived in my opinion
  • 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 print conic sliced models with 20-25° cone angle, hence print 90° overhangs from a central point, and behave partially like a 4-axis printer
  1. 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

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

Conic- or angled slicing is recommended in order to print with Rotating Tilted Nozzle (RTN) or post-processing of existing horizontal sliced G-code is required to provide additional Zrot information to print in good quality.

Conic Sliced on 5-axis PAX

and nearly the same with PAX90 (tilt angle 0..90° only) with shorter arm:

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:

References

That’s it.

3D Printing: 90° Overhangs without Support Structure with Non-Planar Slicing on 3-axis Printer

Updates:

  • 2021/03/22: slicer4rtn released, see announcement
  • 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.

But if . . . one slices non-planar? That’s what I thought about for a couple of years and kept it in the back of my mind. In January 2021 I came across Rotating Tilted Nozzle (RTN) aka RotBot as developed by ZHAW University of Applied Sciences Zurich (Switzerland). I began to design my own approach of the printhead and then started to code my own conic slicer (slicer4rtn), as the paper which might explain it wasn’t published yet by ZHAW.

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° angle
slicer4rtn --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

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:

Conic Slices

  • conic sliced overhangs need to be going out- or inward from a central point
    • 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

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
    • Cura Engine: not yet
    • see Conic Slicing for RTN for up-to-date list
  • support skirts (again): due the slicer algorithm the skirt must omitted before pre-processing but be added at last stage or post-processing
  • redesign my part cooler so I can test print larger overhang pieces
  • find collision algorithm (along with given parametric printhead geometry), that’s part of the 4-axis and 5-axis slicing procedure
  • integrate it sub-volume segmenting framework to print complex pieces too

Gallery

2-sided overhang model nr 4 (conic sliced)

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 . . .

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:

OK print so far, better than anticipated, but still a way to improve it. Reprint with a newer version of slicer4rtn (0.2.3):

  • 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.

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.

This is truly promising, up to 100° overhangs printable with vertical nozzle as mounted on most 3-axis 3D printers . . .

Slicer4RTN Settings

As of the publication of this blog-post (2021/03) no slicer is available but slicer4rtn will 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):
        • M203 Z8, 8mm/s => 8 revolutions/s => 1600 full steps/s: FAILED (blocked motor)
        • M203 Z6, 6mm/s => 6 revolutions/s => 1200 full steps/s: FAILED (stuttering motor at times, mechanical not reliable)
        • M203 Z4, 4mm/s => 4 revolutions/s => 800 full steps/s: OK
        • M203 Z3, 3mm/s -> 3 revolutions/s => 600 full steps/s: OK
    • leadscrew T8x2 (2mm lead per revolution) might support ~12mm/s
    • leadscrew T8x8 (8mm lead per revolution) might support ~50mm/s (ideal, matching X and Y)
  • slow down perimeter (overhangs): use --external-perimeter-speed=20% or a bit more, it prints overhangs better, leave it at 50% if prints look good
  • X- and Y axis speed: try to match your Z speed, so the overall printing is evenly:
    • Slic3r
      • perimeter-speed
      • bridge-speed
      • infill-speed
  • miscellaneous hints:
    • slicer setting solid-infill-below-area = 10 (make infill work at small(er) pieces too)

Models

References

That’s it.

3D Printing: Conic Slicing for Rotating Tilted Nozzle (RTN) / 4 Axis

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:

  • 2021/09/28: added reference to paper by ZHAW describing slicing procedure
  • 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.

I also adapted some of the notions Wüthrich introduced in the Novel 4-Axis 3D Printing Process to Print Overhangs Without Support Material paper, e.g. “outside-cone” and “inside-cone” printing as featured in an earlier blog-post already.

Non-Planar Conic Slices

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.

Theory

In a nutshell the steps are following:

  1. sub-divide faces of the model (fine-grained)
  2. map model to inverse conic space
  3. send to slicer
  4. remap G-code to conic space
  5. adding Zrot to G-code

Conic Space Mapping

(x1,y1,z1,rot) = conicSpaceMapping(cx,cy,x,y,z,dir);

whereas

  • cx, cy are the conic axis coordinates
  • x, y, z are the input coordinates
  • x1, y1, z1 are the output coordinates
  • rot the rotation angle x,y vs cx,cy
  • dir is either direct (default) or inverse
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:

20mm Cube Conic Sliced

Snapshots of progress of conic sliced 20mm cube:

20mm cube conic sliced G-code
20mm cube conic sliced with rotating tilted nozzle simulation

Overhang Conic Sliced

Snapshots of progress of conic sliced Overhang:

Conic sliced overhang model
Conic sliced overhang model including rotating tilted nozzle simulation

Gallery of Conic Sliced Models

Detailed snapshots of overhang nr 3

Detailed snapshots of model nr 6 (table-like)

Some more models with their in-between states, using Cura as model and G-code viewer:

Issues to Resolve

  • test actual G-code in real life
  • 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
  • slice more complex parts
  • document all details
  • release source code to public

Close-Ups

Some close-ups of conic sliced models:

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.

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

  1. map model inverse conic
  2. slice model
  3. map G-code direct conic

inside-cone mode

  1. map model direct conic
  2. slice model
  3. 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:

% slicer4rtn --subdivide=5 --recenter cube.stl
== Slicer4RTN 0.4.1 ==
processing 'cube.stl':
   1/5 read stl
      1/5 subdivide (44 vertices)
      2/5 subdivide (188 vertices)
      3/5 subdivide (764 vertices)
      4/5 subdivide (3068 vertices)
      5/5 subdivide (12284 vertices)
   2/5 map vertices
   3/5 write temporary stl
   4/5 slice (slic3r) stl
=> Processing triangulated mesh
=> Generating perimeters
=> Preparing infill
=> Infilling layers
=> Exporting G-code to ./temp-603919.gcode
Done. Process took 0 minutes and 1.362 seconds
Filament required: 710.9mm (5.0cm3)
   5/5 remap gcode to 'cube.gcode' (16214 lines)
== took 3 secs total, done.

I gonna released Slicer4RTN eventually 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)

Test Prints

As soon I built the RTN printhead on one of my printers I will post photos of the first prints. For now (2021/03) I only printed conic sliced pieces on a 3-axis 3D printer.

References

See Also

With conic sliced G-code there are many first layers . . .

That’s it.