Arachne Variable Line Width Complete Guide: Settings, Classic Comparison, and Practical Examples for OrcaSlicer and PrusaSlicer

For decades, slicers have treated 3D models like onions—concentric shells of fixed width. With a 0.4 mm nozzle you get a 0.4 mm line. But what if the wall is 0.6 mm thick? The slicer either leaves a gap or zigzags to fill it.

The Arachne engine (now integrated into Cura, PrusaSlicer, and OrcaSlicer) changed this by dynamically varying flow to fill gaps perfectly. But that’s just the beginning. This article covers Arachne’s technical workings, slicer settings, when to choose Classic mode instead, and the next-generation technologies beyond variable line widths.

What Is the Arachne Engine? Technical Mechanics of Variable Line Widths

Arachne is a perimeter generation engine developed from a 2020 research paper by Tim Kuipers et al. at TU Delft (Delft University of Technology). The name comes from the thread-spinning woman of Greek myth.

Traditional slicers use fixed line widths. A 0.4 mm nozzle always draws 0.4 mm lines. If a wall is 0.6 mm thick, one line leaves a 0.2 mm gap; two lines overshoot by 0.2 mm. This “in-between thickness” has been a perennial slicing headache.

Arachne uses a Medial Axis Transform—a geometric method—to dynamically calculate the optimal extrusion width for every part of the model. A 0.6 mm wall becomes two 0.3 mm lines. A 1.1 mm wall becomes 0.4 + 0.4 + 0.3 mm. Zero gaps, zero overlap.

This technique shines on walls 1–3× nozzle diameter in thickness: figurine fingers, text and logos, organic curved surfaces—any model with thin features sees a dramatic quality boost.

Arachne-Compatible Slicers and Adoption Timeline

• Cura 5.0 (April 2022 onward): Arachne’s birthplace. Ultimaker implemented Kuipers’ research and made it the default engine from 5.0. No toggle—Arachne is always on.
• PrusaSlicer 2.5.0 (2022 onward): Introduced Arachne as a perimeter generator option alongside Classic (legacy mode).
• OrcaSlicer: Built on PrusaSlicer, it inherits Arachne. Switch between “Arachne” and “Classic” under Wall Generator settings.
• Bambu Studio: A PrusaSlicer fork, so also Arachne-compatible.

Classic vs Arachne: Which Should You Use?

When Arachne Wins

• Text and logos: Characters that collapsed with fixed-width lines print crisp and legible.
• Organic curves: Curved walls outside of vase mode come out smoother.
• 0.6 mm nozzle fine printing: Arachne lets a 0.6 mm nozzle retain 0.4 mm-level detail while cutting print time by ~30 %.
• Figures and miniatures: Thin protrusions like fingers and ears print noticeably better.

When Classic Wins

• Seam quality matters: Arachne has a known issue of leaving gaps at seam points on thin-wall box shapes.
• Large nozzles (0.6 mm+): Tiny holes in top layers have been reported.
• Gap Fill needed: Some Gap Fill settings don’t work in Arachne mode.
• Simple shapes, speed priority: Functional box-like parts often print more reliably in Classic.

Generative Slicing: Thinking Inside the Volume

The next frontier—featured in experimental tools and upcoming AI slicer modules—is generative slicing. Instead of just tracing perimeters, algorithms analyze a part’s structural requirements:

• Stress-adaptive infill: Increase infill density only where FEA analysis indicates high stress.
• Variable extrusion width: Thicken walls at corners that need strength; thin them on straight runs for speed.

Arachne Settings Guide (OrcaSlicer / PrusaSlicer)

Basic Settings

• Wall Generator: Select “Arachne.” Found under Print Settings → Quality.
• Minimum Feature Size: Features thinner than this are skipped. Default is 25 % of nozzle diameter (0.1 mm for a 0.4 mm nozzle). Setting it too low produces garbage-like micro-lines.
• Minimum Wall Width: Specified as a fraction of nozzle diameter. Default works for most cases.

Transition Settings (Advanced)

• Wall Transition Length: The blending distance where wall count changes. Larger = smoother transitions but longer print times.
• Wall Transition Angle: Wedge-shaped areas steeper than this angle won’t add extra walls. Smaller = fewer added walls but possible gaps.
• Wall Transition Filter Margin: Prevents rapid wall-count toggling. Larger = more stable but less precise.

Important: Enabling Arachne automatically disables “Detect Thin Walls”—Arachne handles thin walls natively, so no separate setting is needed.

Known Arachne Weaknesses and Workarounds

• Seam gaps: Visible gaps at seam points on thin-wall (2-wall) box shapes. Fix: set Seam Position to “Nearest” or switch to Classic.
• Top-layer pinholes (0.6 mm nozzle): Small holes in top surfaces with large nozzles. Fix: add 1–2 extra Top Shell Layers or switch to Classic.
• Slower slicing: Arachne’s variable-width calculations are heavier than Classic. Large models take noticeably longer to slice.
• Z-axis artifacts: Rare but possible on models with frequent wall-count changes. Increase the Transition Filter Margin to mitigate.

Why “Size” Matters (Again)

Exploiting variable flow demands a hotend with massive volumetric throughput. Trying to push 0.8 mm width at 300 mm/s through a 0.4 mm nozzle will overwhelm a standard heater—volcano-style heater blocks are required. This is where “Plus”-sized large-format machines find their niche.

Recommended Beast: CoreXZ Sling Hybrid

Creality Ender-3 V3 Plus — A CoreXZ motion system (enabling fast Z-hops for non-planar slicing) paired with a huge 300 × 300 × 330 mm build volume. Its Unicorn quick-swap nozzle integrates with the heatbreak, maintaining stable flow when extruding variable widths from 0.4 to 0.8 mm. The ability to print at 600 mm/s with adaptive layer time compresses cosplay armor and architectural model projects from weeks to days.

Practical: How Print Results Change with Arachne ON vs OFF

Case 1: Printing Text

Printing “HELLO” at 10 mm height: In Classic mode, fixed line width causes uneven stroke thickness in letters like “E” and “L”—gaps in thin strokes and messy Gap Fill in thick ones make text look ragged. Arachne auto-adjusts extrusion to each stroke’s width, producing uniform, legible characters.

Case 2: High-Speed Printing with a 0.6 mm Nozzle

Printing a 3DBenchy with a 0.6 mm nozzle: Classic mode leaves gaps in the hull’s thin walls. Arachne adjusts extrusion width from 0.3 to 0.6 mm to match wall thickness, retaining near-0.4 mm nozzle detail while cutting print time by about 30 %. The “0.6 mm + Arachne” combo is one of the best productivity-quality trade-offs available.

Case 3: Organic Figures

Fingers and ears on a human figure, where thickness varies between 1–3× nozzle diameter: Classic mode may make fingers uniformly thick or skip them entirely (“too thin” by the slicer’s judgment). Arachne processes features down to Minimum Feature Size, reproducing natural thickness transitions.

FAQ

Is Arachne only available in Cura?

No. It debuted in Cura 5.0 but is now in PrusaSlicer 2.5+, OrcaSlicer, and Bambu Studio. The same principle drives all implementations.

Does Arachne stress the printer hardware?

Not really. Arachne is a slicer-side computation; only the E-values (extrusion amounts) in G-code change. That said, models with rapidly varying extrusion widths perform more consistently on direct-drive extruders than on Bowden setups.

Does Arachne work with TPU, PETG, and other flexible materials?

It does, with caveats. Flow-control-sensitive materials like TPU can suffer from abrupt width changes. Set Minimum Feature Size slightly higher (0.15 mm+) and drop print speed to 20–30 mm/s for stability.

0.4 mm or 0.6 mm nozzle—which is better with Arachne?

Depends on the job. For precision figures and text, 0.4 mm is more stable. For functional parts and large models at high speed, 0.6 mm + Arachne cuts print time by ~30 % while holding 0.4 mm-level detail. Test-print first with 0.6 mm, since seam and top-layer issues are more common.

Enabling Arachne slowed down my slicing. What can I do?

Arachne’s variable-width math is heavier than Classic, especially on models over 500 k polygons. Reduce polygon count (Blender’s Decimate modifier helps) or test-slice in Classic, then switch to Arachne for the final print.

Can Arachne and Vase Mode (Spiral Vase) be used together?

Technical issues have been reported. Vase mode prints a single spiral path, and Arachne’s variable widths can cause unintended travel moves or extrusion inconsistencies. For vase-mode wall-thickness adjustment, controlling nozzle diameter and Flow Ratio is more stable.

Conclusion: Use Arachne by Default—But It’s Not a Silver Bullet

The Arachne perimeter generator is one of the most important innovations in FDM 3D printing. Born from TU Delft research, it was adopted by every major slicer within a few years and is now the de facto industry standard.

The strategy is simple: use Arachne by default and fall back to Classic when issues arise. For text, logos, and figures, Arachne’s benefits are enormous; for simple functional parts where problems appear, just toggle back to Classic.

And as noted at the start, Arachne is only the beginning. When stress-adaptive infill and AI slicing reach production, 3D printing quality and efficiency will leap forward again. We are transitioning from “2.5D” manufacturing—flat stacked layers—to true 3D toolpaths. The slicer is no longer a mere translator; it’s an optimization engine. Trust the variable line width.

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