Hybrid Supports for UltiMaker Cura

WORK IN PROGRESS: MANY FEATURES MAY BE BROKEN (proof of concept, 0.6.6-wip)

Sliced inside Cura 5.13.0 (Linux AppImage) with the Elegoo Neptune 4 profile. Not yet test-printed. Windows and macOS untested. Coming from 0.1.x? See What changed.

Licence: PolyForm Noncommercial 1.0.0. Source-available, free for personal and other non-commercial use; commercial use needs permission. Provided as-is, with no warranty and no liability. This is not legal advice.

A Cura tool plugin that supports tall overhangs with one hollow pillar per overhang instead of a forest of solid columns. Each pillar stands on a clear spot (the plate or the model), has base gussets that are kept clear of the model, and ends in a hollow star of lobes: a pseudo-cone whose arms flare out at 45° towards the corners of the overhang. Every layer is one closed outline, and the gaps between the lobes are short enough to bridge; extra lobes are added only where a bridge would be too long. A plain hollow cone with spokes inside is still there as an option.

Cura 5.13.0 screenshots of a synthetic test part shaped like an "EN4 Rugged Box" (70 × 40 × 120 mm, standing on end, open on one side, with ribs, hinge knuckles and a latch lug), taken on a headless test machine with software rendering.

What a real slice looks like

Five layers from the gcode Cura 5.13 produced for that box (Elegoo Neptune 4 profile, 0.2 mm, Generate Support off, Support Wall Line Count 0):

Low down every support is a hollow ring. Higher up, hollow lobes grow out of the centre ring, and just under the ceiling they reach the four corners, with a fifth, shorter lobe towards the open front edge (the only edge not resting on a wall). Each lobe prints as a closed loop, even with Cura's default of 0 support walls. An automated check confirmed that every pillar prints on 100 % of its layers (the 0.1.x "tube in mid-air" problem).

How it compares (the box above, Cura 5.13 estimates, Neptune 4 profile)

These numbers are from 0.3, when the towers were Cura support meshes. Since 0.6.1 Lobes, Cone and Branch print as hollow walls (see below); they have not been re-measured on the box.

On this part the Lobes head uses about 78 % less support filament than Cura's normal support and saves about 40 minutes. Against Cura's tree support it is about 25 % less support filament and about the same time. Against the cone it saves about 10 % of the support filament and a minute. 1 support wall costs about 18 minutes and isn't needed for the lobes. These are Cura's own estimates for one synthetic part; nothing here has been printed, and tree support may well do better on other shapes.

📄 The research paper: Putting Plastic on a Pedestal: experimental methods of plastic waste reduction for 3D printing (a defensive publication describing these supports; physically untested; its own repository is putting-plastic-on-a-pedestal).

New in 0.6.4: big parts, measured

Sliced on 200 x 200 mm parts with long stems (Cura 5.13, Neptune 4; not yet printed): Hybrid lobes use 84 % less support plastic than Cura's normal support on a 150 mm-tall part, and 24 to 26 % less than Cura's tree support (but 29 % more than tree on a 50 mm-tall part, so the saving is a tall-part effect). Full table in docs/RESEARCH.md section 16. Also fixes cone shells that flared past the edge of big overhangs.

New in 0.6.3: an interface cap on every support

From the review of 0.6.2: the towers had no support interface, so the part's underside would have printed straight onto a few walls and drooped between them. Every Lobes, Cone, Branch, Solid and Conform support (and Tethers that fall back to lobes) now gets the same 4-layer cap stack as the tethers, 0.8 mm under the overhang:

1. a lattice (3 mm spacing) bridging between the tower's walls, printed at Bridge speed (20 mm/s) with the fan at 100 %,
2. a second lattice the other way,
3. a full layer of concentric rings at 50 %,
4. a solid (100 %) layer, then the usual contact gap (0.2 mm) and the part.

The towers now stop at the cap's underside, so the first lattice bonds straight onto them. The cap is its own small mesh (HybridCap), printed as solid skin in Cura's preview; the lattice / rings / solid layers are written into the G-code when you Save to Disk or send to the printer, as for the tethers (untick Cap stack to keep plain solid layers). Nothing in your Cura profile is changed for it. A sloped or curved underside gets a staircase of flat caps, one per 0.8 mm of height; where a cap can't fit (an overhang less than about 1.4 mm above what's under it, a steep curved underside, or no room clear of the model) there is none, and the tower reaches the underside as before. On the six-part plate Cura's estimate went from 2 h 14 min to 2 h 21 min, about 0.2 m more plastic per part.

New in 0.6.2: wide rounded lobes with filleted joins

From the review of the 0.6.1 top view: the thin walls met at the centre in sharp notches (stress raisers), and each was a 2-line slab whose two lines sit 0.4 mm apart, so it bends easily sideways when the nozzle drags across it. The Lobes support built to size is now one star of a few wide rounded lobes (8 mm wide by default, lobe_width), printed hollow with 2 walls (Tube walls). The two walls of each lobe are about 8 mm apart, so it is far stiffer sideways, and the lobes blend into each other with rounded inner corners (at least 3 mm, lobe_fillet) instead of notches. Being wider, fewer are needed: 4 lobes on the 40 mm channel and corner, where 0.6.1 had 6 walls. Each lobe still stands on the bed as far out as it must and flares at 45° to the overhang's edges.

Branch and the Cone's ribs stay thin straight webs (that's what those heads are), but their centre now has a rounded hub, so they no longer meet in a sharp notch either.

On the six-part plate (Cura 5.13, Neptune 4, measured as in 0.6.1): channel lobes 0.73 m (0.6.1: 0.65 m), corner lobes 0.65 m (0.57 m), so about 0.08 m more plastic each for the stiffer shape. The curved outlines take more, shorter moves (about 15,000 against 3,600 per part). Cura's estimate for the whole plate went from 2 h 6 min to 2 h 14 min, partly from Branch, which now prints its 3-line webs solid (2 walls) instead of as a loop with a gap.

New in 0.6.1: hollow walls, and one tower where 0.6.0 made four

From the first look at 0.6.0 in Cura on the Neptune 4:

• The towers print as hollow walls, not zig-zag. Cura fills a support mesh with the support pattern, and with the Neptune 4's Support Wall Line Count of 0 that is one zig-zag line with no outline (Cura won't let a plugin change support walls or pattern for one mesh). 0.6.0 made the walls about 3 mm thick to stop them going missing, and they printed as a zig-zag inside a 3 mm strip. Now every Lobes, Cone and Branch support (and the standing webs) is added as a normal printed mesh with its own settings: one wall round every outline, no infill, no top or bottom skin, printed at your support speed and flow. A 2-line wall prints as one closed loop, the tube as two rings, the lobes as closed loops. Tethers and the Solid/Conform heads stay Cura support meshes (they need the roof and the concentric pattern). In Cura's preview the towers show in the wall colour, not the support colour.
• One tower instead of 4, 8, 16 or 32. When the overhang needed one support built to size, 0.6.0 asked for a clear round foot as wide as the reach (it hit the legs of a channel), and any support standing on a surface instead of the bare bed (a base plate under the part, a brim block, a floor of the model) saw that surface as "model above the wall", built nothing and split the overhang again and again. Now each wall of the criss-cross stands on the floor along its own line as far out as it must, and only a small foot round the centre has to be clear. On a channel or corner 8 to 25 mm high, 30 to 60 mm wide and 40 to 80 mm long, standing on a base plate, every head now makes 1 support (0.6.0: 1 to 32).
• On the six-part plate (Cura 5.13, Neptune 4): channel lobes 0.65 m of filament and 3,600 moves (0.6.0: 0.78 m, 8,500), channel branch 0.64 m and 3,000 (0.77 m, 8,500), corner lobes 0.57 m and 2,700 (0.66 m, 7,900); the cones are about the same (1.30 m, 21,700 moves). Measured from the G-code between the legs, so these include a little of the parts' own first layers.

One criss-cross built to size (Lobes and Branch)

When one normal-sized tower can't reach the whole overhang within the 45° flare (a 40 x 40 mm roof only 15 mm up, say), Lobes and Branch build one support to fit instead of several towers: thin walls (2 lines thick for Lobes, branch lines for Branch) from one centre point with no hub, each standing on the floor along its own line as far out as it must and then flaring out at 45° to the edge of the overhang. The first go to the corners (a criss-cross); more are added only where a bridge would be longer than Max bridge span, counting edges that rest on a wall of the model as supported. On the 40 mm test channel that is 6 walls (four to the corners, two to the open ends) and 0.58 m of support, against 1.21 m for four lobes towers. Bigger overhangs still split. (lobes_one_tower in the settings turns it off.) Cone does the same with one thin cone (a 2-line wall from a circle on the bed, flaring to the overhang's edges) round an X of ribs to the corners: on the channel 0.92 m of support against 0.58 m for the criss-cross, and about 2.5 times the moves, so it may be dropped after the test print.

Experimental: Tethers

Instead of a pillar from the floor, Tethers strings strips of support between two walls of the model a short way under the overhang (10 mm by default), and puts a 4-layer cap on top (see below). The idea comes from failed supports: the loose "fuzz" catches on nearby walls and builds up into something solid.

• Tethers: straight strips from wall to wall. The first and last sit at the two ends of the overhang (0.2 mm in from the edge), the rest evenly between, covering about 20 % of the space. Each prints as a pair of straight lines, so its first layer is a proper bridge. Every other layer is shifted half a line width, so the layers only half overlap and snap apart easily. Cura can't do that shift from the shape (see docs/RESEARCH.md section 10), so the plugin shifts those lines in the G-code when you Save to Disk or send to the printer. Cura's preview shows the strips without the shift.
• Dropped after the first sliced test plate (0.6.0): stepped tethers (no advantage over straight ones), the spiderweb (left large regions unsupported) and radial tethers (the fan plus a lobes tower for the far corner was the worst of both; one lobes tower built to size does the job). Their notes stay in docs/RESEARCH.md.
• Slow first layers: the first three tether layers (0.6.5; was two, in case the first are weak or slack) are treated as bridges in mid-air, and Cura prints support at the profile's support speed (165 mm/s on the Neptune 4). On save, the plugin slows those layers to Bridge speed (20 mm/s by default; 0 turns this off) with the part fan at 100 %, then puts speed and fan back. This adds about a minute that Cura's time estimate doesn't show.
• The cap is kept clear of the walls by your normal X/Y distance. Only the strips touch the walls.
• The cap stack (0.8 mm, 4 layers, written into the G-code when you save, so Cura's preview shows ordinary roof lines instead): a lattice across the tethers (3 mm spacing, first layer at Cap flow, 85 % by default, so the hot bead fuses with the thin tether instead of squashing it), a lattice along them, one full layer of concentric rings at 50 % fill, then a solid (100 %) diagonal layer, so the part's underside comes off a smooth, flat surface. Untick Cap stack in the panel to go back to Cura's plain roof.
• Test prints first: test-prints/ has one Neptune 4 G-code with every head on a 40 mm channel and corner, with what to look for (test-prints/README.md).

• It only works where an overhang has walls on two opposite sides, no more than 110 mm apart (warning over 90 mm, falls back to lobes past 110). Anything else, such as the box's outside ribs, falls back to lobes automatically, and the status line says so.
• It changes some of Cura's own settings, because Cura only lets you set them for the whole print, not per support:
  • Support X/Y Distance goes to 0. Cura keeps every support that far from the walls, so otherwise the strips stop short. The plugin's other supports and the cap keep their own clearance in their shape.
  • Support Roof is turned on, 0.8 mm thick (the cap stack's four layers; 2 mm with the stack off).
  • Support Pattern goes to concentric, so every strip prints as an outline of its own shape, and Support Infill Line Directions is set along the strips.
  • Remove puts them all back. (Undoing a Remove brings the meshes back but not the settings; press Generate again.)
• The strips touch the walls, so expect small marks where they break off.
• Not printed successfully yet. The first test (stepped tethers on the old test box) showed the strips were too sparse and the roof touched the walls; both were fixed in 0.5.0, and the cap stack and slow-bridge step are new in 0.6.0. Whether the first mid-air layer holds at your printer's support speed is still the big unknown.

What changed since 0.1

From the 0.1.x feedback on the EN4 Rugged Box:

How it works (short)

1. Select a model and press H (or click the Hybrid Supports tool on the left toolbar).
2. Press Generate. For every overhang the plugin:
   • finds one spot where a pillar can stand with a clear column down to the plate or the model,
   • builds a hollow tube with gussets at its foot, trimmed to stay clear of the model,
   • builds a hollow star of lobes that flare (at most 45°) from the tube out to the corners of the overhang, adding lobes until no bridge is longer than Max bridge span (edges that rest on a wall of the model count as support),
   • gives low overhangs (6 mm or less) thin standing webs instead,
   • adds a thin support blocker over the overhang so Cura's own automatic support doesn't fill the same area again.
3. Slice as usual. Lobes, Cone and Branch supports are added as normal printed meshes set to print as hollow walls (one wall, no infill, no top or bottom, at your support speed and flow); Tethers and the solid heads are Cura support meshes. Either way they print even when Generate Support is off.

The full explanation is in HOW_IT_WORKS.md; the research behind it is in docs/RESEARCH.md.

Use

• Remove deletes the generated meshes for the selected model (or for all models if nothing is selected).
• Pressing Generate again replaces that model's previous supports.
• The generated meshes are children of the model, so they move with it. Re-generate after rotating or scaling.
• The status line tells you how many supports were made, which ones the model only lets the head reach partly, and when gussets were shortened.
• Since 0.6.1 the towers print as walls, so Cura's Support Wall Line Count and Support Pattern no longer matter for them (they still do for Tethers and the solid heads). To go back to support meshes, set print_walls = False in hybrid_core.py.
• Cura's Support X/Y Distance is respected: the plugin builds its meshes that far (plus 0.1 mm) from the model. (Printed as walls, Cura doesn't add that gap itself, so the clearance is in the shape.)

Gusset height trades stiffness for plastic and time. On a 50 mm test tower (0.1 geometry), going from no gussets to 24 mm added about 8 % to the support mesh volume.

What exists and what doesn't

Source code: The-Dorkknight/cura-hybrid-supports on GitHub