Tag Archives: Rotating Tilted Nozzle

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

by Rene K. Mueller · published April 19, 2021 Technology Non-Planar Slicing, Overhang Printing, Penta Axis (PAX), Research Paper, Rotating Tilted Nozzle, Rotating Variable Tilting Nozzle, Sub-Volume Segmenting

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:

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:

*2 segments: z-planar, conic* (outside-cone)

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:

*bottom: inside-cone, top: outside-cone*

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:

*2 segments: planar (bottom), conic with center offset (top)*

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)*

*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.

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*

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

[Coyetaux, Crook, Pauwels, Whelan] 5-Axis 3D Printing (2018) – free paper (PDF)
[Wuethrich, Elspass, Bos, Holdener] Novel 4-axis 3D printing process to print overhangs without support material (2020) – non-free paper (PDF)

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

by Rene K. Mueller · published February 26, 2021 Technology 4 Axis, Conic Slicing, Non-Planar Printing, Non-Planar Slicing, Rotating Tilted Nozzle, RotBot, RTN, Slic3r, Slicer4RTN

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.

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:

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:

sub-divide faces of the model (fine-grained)
map model to inverse conic space
send to slicer
remap G-code to conic space
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 with rotating tilted nozzle simulation

Overhang Conic Sliced

Snapshots of progress of conic sliced Overhang:

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
- ~~verify Axxx / Z_rot~~ , verified with G-code simulator coded with OpenSCAD
- verify Exxx interpolation (some experiences with printing with vertical nozzle)
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**

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

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

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:

% 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

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

3D Printing: Rotating Tilted Nozzle 4th Axis Option – Draft

by Rene K. Mueller · published January 27, 2021 Technology 4 Axis, Conic Slicing, Rotating Tilted Nozzle, RotBot, Z rotation, ZHAW

Status: just collecting information and start a simple design

Updates:

2021/03/13: fallback printing horizontal slices animation added
2021/03/01: added brief animation of simulated print of conic sliced overhang model
2021/02/23: added brief animation (Zrot=-180° .. 180°)
2021/01/31: maturing printhead with heatsink fan and part cooler
2021/01/28: Outside/Inside Cone printing explained with example, Considerations (Pros/Cons) added
2021/01/27: more detailed illustrations and slicing renderings, published as a draft
2021/01/22: adding conic slicing examples
2021/01/21: first version with rotating bowden printhead

I will update this blog-post as I progress or find other people with alike ideas and summarize the findings.

RotBot by ZHAW School of Engineering Zurich

As featured on Hackaday January 16, 2021 and other sites, a “Novel 4-Axis 3D Printing Process to Print Overhangs Without Support Material” by ZHAW School of Engineering (Zurich, Switzerland), from the abstract of the paper:

[..] a novel 4-axis FDM printing process with a newly designed printhead, for the printing of overhangs without support structures. With conventional FDM printing, overhangs of more than 45deg–60deg must be supported.
For this novel printing process, the printhead is rotated 45° around a horizontal axis and equipped with a vertical, rotational axis. The printhead no longer follows layers parallel to the build platform, but moves on the surface of a 45deg cone. The printing cone increases in diameter from layer to layer. With this cone-shaped layers, the printable angles increases by 45°, which leads to printable overhangs of up to approximately 100°.
New slicing strategies for this printing process have been developed to slice the parts for the novel printing process. The feasibility of the concept has been prototypically demonstrated. The novel design achieves the advantages of higher speed and quality with lower cost at the same time.

A brief video sequence of printing (YouTube) shows the machine movement. Unfortunately, as of 2021/01 not much more details have been published by ZHAW except a paywalled paper [sigh] which contains useful overview of their research. I contacted ZHAW and Michael Wuethrich mentioned that they are in negotiations with different companies to develop a product (2021/01) and eventually release the details of their slicing approach with pre- and post-processing while using an ordinary slicer.

Update 2021/02/27: I started with a 4-axis conic slicer.

Rotating Tilted Nozzle (RTN) Option

I thought to try my own implementation of this Rotating Titled Nozzle 4 Axis option. The main idea to keep the entire hotend in Bowden style and rotate that around only once (non-continuous) with all wires, that would simplify things greatly:

The challenge is the +/-180° position when the nozzle opening looks forward, where the printhead bowden tube (and all cables) comes most close to the X beam. As a consequence only -180° to +180° rotation is allowed and not multiple revolutions.

It would also mean, once the printhead reaches -180°, and it has to rotate to +180° and decrease from there again to fulfill 360° rotation – whether this is suitable has to be seen, this likely creates a seam there.

The main advantage of this simplified 4 axis approach is to use existing pieces plus just an additional NEMA 17 motor.

Update 2021/01/26: Wuethrich from ZHAW mentioned that they started first also with a full printhead rotating but then switched to the more complex continuous rotating printhead to avoid a seam, have direct drive extruder, faster prints as simpler decision making to change rotation direction and no start/stop of rotation and de/acceleration when reaching -180/+180° position.

Single Revolution with Rotation Shadow

As I pondered on the limits of single rotation approach, there is a range where the bowden tube (and all wires with it) is touching and bending on the X carriage or printhead holder – let’s call it the rotation shadow – ideally it would be zero or slightly sub-zero to have a bit overlap to conceal a possible seam with “ironing” the section (move nozzle over section without extruding).

E3D Volcano

My first attempt is modeling with E3D Volcano hotend like the RotBot by ZHAW:

Micro Swiss / CR 10 Hotend

And as alternative the smaller Micro Swiss / CR 10 printhead which gives significant more space for the bowden tube (and all wires with it) to bend or flex near -180/+180°:

Comparison Volcano vs Micro Swiss

At this point I continue with the Micro Swiss option, as the smaller heatsink gives me more space to make full 360° turn with -180° to +180° and have ~0° rotation shadow, perhaps even sub-zero as of overlapping.

Slicing for Rotating Tilted Nozzle: Conic Slicing

I had to visualize the novel conic slicing approach as mentioned in the article and in the video:

*Rotating Tilted Nozzle: Outside Cone – tilted print plane with Z axis rotating leads to conic print plane*

f(Z_rot, C_height, R) ⟹ X, Y, Z

X = sin(Z_rot) * R
Y = -cos(Z_rot) * R
Z = C_height / sqrt(2)

Z _rot = atan2( -Y, X )
R = sqrt( X*X + Y*Y )
C_height = Z * sqrt(2)

A single conic slice is covered by Z_rot, C_height and R, whereas slices are separated by increasing Z offset to C_height, forming conic slices on top of each other:

Let’s inspect the motion of a single layer: it’s curved – obviously – in X, Y and Z – this means, the Z axis has way more motion than in cartesian XZ Prusa-Mendel setup where the Z axis only changes once a layer is finished, here with cone-slicing every trace or track all traditional 3 axis are in motion, plus the 4th – the tangent on that conic trace.

Multiple solids sliced planar and in conic manner

See more details on Conic Slicing for Rotating Tilted Nozzle (RTN).

Different Print Modes

The 45° tilted printhead allows three print modes:

non-rotation nozzle with planar Z layers (with ordinary slicer), acts like belt-printer in one direction: overhangs in one direction without support
rotation nozzle with planar Z layers (requires dedicated slicer), might support near 90° overhangs of a certain length in all X/Y plane directions as well – but needs to be tested
rotation nozzle with conic Z layers (requires dedicated slicer or pre- and post-processing while using ordinary slicers)

And by choosing the position of the “axis” of the conic slicing within the model and the cone direction matters then as well:

The last piece with inside and outside looking overhangs requires a switch of nozzle direction, e.g by default the sliced cones are ordered ▲ (outside-in or outside-cones) where outward overhangs work, but for inward overhangs the opposite direction of the nozzle looking outside is required ▼(inside-out or inside-cones), like this piece:

*Vertical splitted: bottom half with overhang toward cone axis Inside Cone print,*
*upper half with overhang away from cone axis Outside Cone printing,* **all without support**

So the slicing software needs to recognize this, and the sliced cones switched either ▼ or ▲ according Z level.

These aspects opens a whole new range of considerations how to orient a piece and where to position the newly introduced slicing axis, and which kind of cones need to laid at which level.

Issues to Resolve

Heatsink fan mount: needs to be mounted for both variants, Micro Swiss and E3D Volcano ideally
Part cooler:
- have the part cooler rotate on Z axis as well? yes for now
- ~~using a flexible pipe to blow air near the nozzle instead~~

Z rotation calibration:
- alike with X or Y stop, but a trigger rotating from one direction only and then set a angle offset
Z rotation motor mount adaptable for different kind of printheads
- keep it modular
- ensure the nozzle end is centered (allow simple center calibration)
Properly document design and features of Rotating Tilted Nozzle as there isn’t much detail information available
3D printer firmware support
- Marlin: support for 4th axis?
3D slicing software support
- adapt ZHAW’s approach with pre- and post-processing but use existing slicers; Update 2021/02/26: separate blog-post going into the details of Conic Slicing
- dedicate slicer for conic slicing, e.g. adapt Mandoline Py

Considerations

Pros

conic layers: printing 90° overhangs without support, given some conditions are met:
- overhangs must be horizontally or vertically rotational symmetric and aligned with the cone axis to switch from outside to inside cone printing or vice-versa (to do: more use cases explored and documented)
conic layers: stronger pieces as layers cross X, Y and Z in non-planar manner, mechanical forces distribute further than just planar layers
planar layers / rotating nozzle: perhaps close to 90° overhangs (speculative) requires new overhang algorithms in slicer

Cons

additional mechanical complexity
- fine-tuning nozzle center calibration
additional slicing software complexity
- new slicer software supporting different printing modes (conic layers, planar layers w/ rotating nozzle)
- conic layers: more things to consider (preferably recognized by the slicing software):
  - overhangs must be horizontally or vertically rotational symmetric and align with cone axis to take advantage of it (complex compartmentalizing of different cone-direction per overhang and newly introduced seams between those)

Ashtar K with Rotating Tilted Nozzle (RTN)

The additional Y offset is about 20mm, and losing apprx. 50 mm in Z build volume in its current form:

Ashtar K RTN printing conic sliced overhang model (animated)

Fallback Print Horizontal Slices

Some parts may not require conic slices, e.g. introducing new unprintable overhangs which in horizontal slices would not exist, so a simple way to print traditional sliced models is by adding a proper rotation angle (e.g. G-code A..) so the nozzle extrudes nicely, something like:

Horizontally sliced 20mm cube printing with enhanced G-code with `rtnenhancer`

I wrote a small script called rtnenhancer which converts existing G-code to enhanced G-code.

References

Novel 4-Axis 3D Printing Process to Print Overhangs Without Support Material (english) by ZHAW
Multi-Axis 3D Printing Technique Improves FDM Strength Over 2X (see also paper)

Introduction

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

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

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

Overhang In/Out: 2 Segments: 2x Conic

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

Overhang Out No 5: 3 Segments: 2x Z-planar & Conic

Conclusion

References

See Also

Introduction

Non-Planar Conic Slices

Theory

Conic Space Mapping

Pseudo-Code

Examples

20mm Cube Conic Sliced

Overhang Conic Sliced

Gallery of Conic Sliced Models

Issues to Resolve

Close-Ups

Outside- vs Inside-Cone Printing

Slicer4RTN

Test Prints

References

See Also

RotBot by ZHAW School of Engineering Zurich

Rotating Tilted Nozzle (RTN) Option

Single Revolution with Rotation Shadow

E3D Volcano

Micro Swiss / CR 10 Hotend

Comparison Volcano vs Micro Swiss

Slicing for Rotating Tilted Nozzle: Conic Slicing

Different Print Modes

Issues to Resolve

Considerations

Ashtar K with Rotating Tilted Nozzle (RTN)

Fallback Print Horizontal Slices

References

See Also