Tag Archives: Overhang Printing

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

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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:

  • 2 segments: z-planar, conic (outside-cone)
  • starting z-planar
  • 2nd segment conic on top
  • conic segment going overhang
  • extending both sides
  • extending both sides
  • finished piece
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:

  • 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)

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)
  • 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:

  • 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: Multi-Axis Printing & Overhangs

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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

  • 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

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

  • 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

References

That’s it.

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

by · published Technology , , ,

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

  • 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:

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

  • 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
    • 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 . . .

  • 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 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.