This is a small, purpose-built diagnostic test model created to reproduce a repeatable bridge-related surface artifact observed on a Prusa CORE One.

The model is intentionally simple and minimal. It is not meant as a functional or aesthetic part, but as a controlled test case to help isolate the root cause of the artifact.

What this model is for

Reproducing bridge-related surface defects. Comparing behavior across:

• Different printers

• Different filaments / colors

• Different slicer versions or profiles

Verifying whether the issue is:

• Slicer-related

• Firmware-related

• Hardware-related

• Filament-dependent

What this model is not for

• Strength testing

• Print quality benchmarking

• Mechanical use

Print context (reference setup)

The artifact was reproduced under the following conditions (included for reference only):

• Printer: Prusa CORE One

• Slicer: PrusaSlicer

• Nozzle: 0.4 mm

• Layer height: 0.20 mm

• Material: PLA (multiple colors tested)

• Cooling: Fan changes had no visible effec

• Geometry scaling / rotation: No effect observed

My best settings so far:

• Printer: Prusa CORE One

• Slicer: PrusaSlicer

• Nozzle: 0.4 mm standard brass (not HF)

• Layer height: 0.20 mm

• Material: Prusament PLA

  • multiple colors tested but does not seem to make a difference

• Cooling: 100% Fan

  • changes had no visible effect

• Temperature: 230C.

  • Tried 225-230. 230 seems a fraction better but not significant

• Thick bridges: Seems like a total failure, keep off.

• Bridge speed: 18mm/s.

  • Tried 10-50mm/s

  • 18-27 mms/s seems to be the workable range

  • no speed completely remove artefacts.

• Bridge flow ratio: 1.8.

  • The workable range seems to be 1.75-1.85

  • I tried a lot of combinations of speed and lower/higher bridge flow ratio but higher values lead to more artefacts while lower lead to under extruded bridges not bonding.

I have also tried to adjust the speed of all slicer features to align the volumetric flow rate between the bridge and the other parts of the print. The matching speed for perimeters and infill is about 30mm/s. 

I am not yet convinced this is needed or makes significant difference so consider that optional.

Observed issue

The issue appears early in the bridge section and then stabilises. It repeats across different geometries, I have tried square and rectangular shapes as well but this makes no difference. The bridge angle makes no difference, the issue appears in the early section of the print regardless of where the bridge starts printing.

The issue starts as a bulge upwards early in the first printed bridge strands to collapse in a sag with under extrusion before stabilising into a good bridge for the rest of the print.

Model details

Initially I used rectangular and square models but settled on this circular model as shape seems to make no difference and the circular model is easier to use as it does not need any arrangement on the platter. Designed to include:

• A single extrusion layer controlled bridge

• Immediate transition from solid walls into bridge extrusion

Geometry kept small to allow:

• Fast iteration

• High repeatability

• Easy comparison across setups

Future considerations

• The model is limited to 0.2mm layer height and designed for a 0.4mm nozzle, add more variants for other nozzles and layer heights.

Why this exists

This model exists to support a community debugging effort. If you see the same artifact — or don’t — that information is valuable.