Ultimate Bridge Calibration Test Suite

Ultimate Bridge Calibration Test Suite

A multi-plate bridge calibration suite for dialing in cleaner, stronger, and more consistent unsupported bridges in FDM printing.

This is not just a generic bridge torture test. The included .3mf is set up as a slicer calibration project with per-object settings already applied, so each object tests a specific bridge variable. Open the .3mf directly in OrcaSlicer or a compatible slicer, slice, print, and compare the results. 

There are notes with settings to change near each plate, don’t forget to check and adjust those!

What this helps tune

Use this suite to calibrate:

• Bridge speed

• Internal bridge speed

• Bridge flow ratio

• External bridge density

• Bridge angle/direction

• Thick bridge behavior

• Cooling and fan behavior

• Sagging, drooping, stringing, and weak bridge strands

Bridging depends heavily on filament, temperature, cooling, nozzle size, and slicer behavior, so the best settings may be different for PLA, PETG, ABS, ASA, nylon, PPS, PC, and filled materials.

Important: use the .3mf

The .3mf contains per-object calibration settings.

For best results:

• Open the .3mf as a project

• Do not import it as plain geometry only

• Do not merge or reset object settings

• Check that per-object settings are still applied before slicing

• Use the STL files only if you want to set the calibration values manually

The project was made for OrcaSlicer / Bambu Studio-style workflows. Other slicers may not preserve all embedded settings.

Before printing

The .3mf may also carry printer, filament, bed, and temperature settings from the saved project.

Before printing, verify:

• Printer profile

• Build plate size

• Nozzle size

• Nozzle temperature

• Bed temperature

• Filament type

• Cooling settings

• Flow and pressure advance for your filament

Do not blindly print with the saved machine or filament profile unless it matches your setup.

Plate 1 — Bridge Speed Calibration, Low Range

Plate 1 tests lower bridge speeds:

Included bridge speeds right to left diagonally per object

• 5 mm/s 

• 7.5 mm/s 

• 10 mm/s 

• 15 mm/s 

• 20 mm/s 

• 25 mm/s 

Each object has the bridge speed applied per object. Use this plate first if you are tuning a difficult filament, a hot chamber material, or a material that needs slower bridge movement. Objects are arranged diagonally to mitigate potential cooling influence from the previous towers.

Plate 2 — Bridge Speed Calibration, Higher Range

Plate 2 continues the bridge speed test:

Included bridge speeds right to left diagonally per object

• 30 mm/s 

• 35 mm/s 

• 40 mm/s 

• 45 mm/s 

• 50 mm/s 

• 55 mm/s 

Use this plate after Plate 1 if your filament bridges well and you want to find the fastest clean bridge speed.

Do not simply choose the fastest bridge that survives. Choose the fastest bridge that still looks clean, anchors properly, and gives good top-layer recovery.

Plate 3 — Bridge Flow / Density Matrix

Plate 3 tests bridge flow ratio against external bridge density.

Included flow ratios left to right per column & object:

• 1.1

• 1.2

• 1.3

• 1.4

• 1.5

• 1.6

Included external bridge densities top to bottom per row & object:

• 100%

• 105%

• 110%

• 115%

This plate is useful after you have already selected a good bridge speed from Plates 1 and 2.

The goal is to find the combination that gives the cleanest underside while still producing a strong, closed bridge surface.

Plate 4 — Fan / Cooling Behavior Check

Plate 4 is used to check cooling behavior and fan ramp behavior.

Slice the plate and inspect the preview. Make sure the fan behavior matches what you expect as the tower gets taller.

Useful cooling settings to check:

• Auto cooling

• Minimum fan speed

• Bridge fan speed

• Overhang/bridge fan speed

• Internal bridge fan speed

• Full fan speed layer

• Forced cooling for overhangs and bridges

This plate is especially useful when tuning materials where too much cooling causes warping, but too little cooling causes bridge sag.

Suggested tuning order

For best results, tune in this order:

1. Print Plate 1 and/or Plate 2 to find the best bridge speed.

1. Set your global bridge speed to the best result.

1. Print Plate 3 to tune bridge flow ratio and external bridge density. Each object is labeled with flow ratio & speed.

1. Use Plate 4 to verify cooling behavior.

1. Save the final values into your filament or process profile.

Only change one major variable at a time. Changing speed, flow, density, cooling, and temperature all at once makes the results harder to read. Each plate has instructions with settings & where they should be located. 

How to judge the results

Look at the underside and top recovery of each bridge.

A good bridge should have:

• Straight bridge lines

• Minimal sag

• Good anchoring at both ends

• No broken strands

• Minimal stringing

• A top surface that recovers cleanly after the bridge

Signs the bridge is too slow, too hot, or over-extruded:

• Heavy sagging

• Droopy thick strands

• Blobs at the bridge ends

• Rough underside

• Poor top-layer recovery

Signs the bridge is too fast or under-extruded:

• Broken strands

• Gaps between bridge lines

• Weak anchoring

• Torn-looking bridge paths

• Incomplete coverage

Recommended make/remix info

When posting a make, please include:

• Printer

• Slicer

• Filament

• Nozzle size

• Layer height

• Nozzle temperature

• Bed temperature

• Bridge speed

• Bridge flow ratio

• Bridge density

• Fan percentage

• Whether thick bridges were enabled

This makes the results much more useful for other users.