🌉 Bridging (Bridge Print) Improvement Guide
📋 TL;DR (Summary)
A bridge (köprü) is a print made in the air between two support points. For a successful bridge, settings of fan speed 100%, temperature 5-15°C lower than normal, speed 15-25 mm/s, and flow rate 90-95% are ideal. PLA shows the best bridge performance, while PETG and Nylon are more difficult. The maximum bridge distance is around ~80mm for PLA and ~50mm for PETG.
🔧 What is a Bridge (Köprü)?
A bridge (köprü) is a horizontal print made in the gap between two support points in 3D printing, without any support underneath. Spaces above windows, doorways, or between any two walls are examples of this situation.
In FDM printing, filament normally takes shape by adhering to the layer beneath it. However, in a bridge situation, there is no bottom layer, and the molten filament must be stretched in the air between two points. This situation is one of the most challenging stages of printing.
⚠️ Causes of Poor Bridge Quality
1. High Temperature
Filament that is too hot sags in the air because it cannot solidify fast enough. During bridging, filament should cool and harden as quickly as possible.
2. Insufficient Cooling
When fan speed is low, filament solidifies late and sags downwards due to gravity. Aggressive cooling is essential for bridging.
3. High Print Speed
In fast printing, filament is released before it can stretch sufficiently. Slow and controlled extrusion keeps the filament taut between two points.
4. Excessive Flow Rate
When too much material is extruded, the weight increases, and sagging becomes inevitable. The flow rate should be slightly reduced for bridging.
5. Long Bridge Distance
Each material has a maximum distance it can span without support. When this distance is exceeded, sagging is inevitable.
💨 Fan Speed Optimization
Fan speed is the most critical factor for bridge quality.
Recommended Fan Speeds:
| Material | Normal Print | During Bridging |
|---|---|---|
| PLA | 50-100% | 100% |
| PETG | 30-60% | 80-100% |
| ABS | 0-20% | 40-60% |
| TPU | 30-60% | 80-100% |
| Nylon | 0-30% | 50-70% |
Fan Speed Tips:
- Increase fan to 100% 1-2 layers before the bridge
- Be careful with ABS: excessive fan can cause warping
- It is ideal for the part cooling fan direction to be parallel to the bridge direction
- You will get better results with dual fan systems (4020 fans)
🌡️ Bridge Temperature
Using a lower temperature than the normal printing temperature allows the filament to solidify faster.
Recommended Bridge Temperatures:
| Material | Normal Temperature | Bridge Temperature |
|---|---|---|
| PLA | 200-215°C | 190-200°C (-10 to -15°C) |
| PETG | 230-245°C | 220-235°C (-10 to -15°C) |
| ABS | 240-260°C | 230-245°C (-10 to -15°C) |
| TPU | 220-240°C | 210-230°C (-10°C) |
| Nylon | 250-270°C | 240-260°C (-10°C) |
Temperature Tips:
- Too low a temperature will cause adhesion problems
- Start by lowering 5°C, increase to 10-15°C if necessary
- Use bridge-specific temperature settings in your slicer if available
- Temperature changes have a delayed effect (1-2 layers)
🐌 Bridge Speed
Slow print speed allows the filament to stretch and form a proper bridge.
Recommended Bridge Speeds:
| Quality Level | Speed Range | Description |
|---|---|---|
| Excellent | 10-15 mm/s | Best quality, slow |
| Good | 15-25 mm/s | Recommended starting point |
| Acceptable | 25-35 mm/s | For faster prints |
| Risky | 35+ mm/s | Usually bad results |
Speed Tips:
- Start with 20 mm/s and adjust based on results
- The first bridge layer is the most critical, subsequent ones are easier
- Very slow speeds can also cause problems (excessive heat buildup)
- Speed in the bridge direction is important, not travel speed
💧 Bridge Flow Rate
Reducing flow rate instead of the normal flow rate during bridging reduces sagging.
Recommended Flow Rate Values:
| Material | Bridge Flow Rate |
|---|---|
| PLA | 90% - 95% |
| PETG | 85% - 95% |
| ABS | 90% - 95% |
| TPU | 85% - 90% |
Flow Rate Tips:
- Start with 95%, reduce to 90% if necessary
- Going below 85% will cause gaps in the bridge
- You can set a separate flow rate for the first bridge layer
- Calibrate normal flow rate first, then adjust bridge flow
📏 Bridge Distance Limits
The maximum bridge distance that each material can span without support varies.
Maximum Bridge Distances:
| Material | Easy (<) | Medium | Difficult (>) | Maximum |
|---|---|---|---|---|
| PLA | 30 mm | 50 mm | 70 mm | ~80 mm |
| PETG | 20 mm | 35 mm | 45 mm | ~55 mm |
| ABS | 25 mm | 40 mm | 55 mm | ~65 mm |
| TPU | 15 mm | 25 mm | 35 mm | ~40 mm |
| Nylon | 20 mm | 30 mm | 40 mm | ~50 mm |
⚠️ These values are approximate values obtained with optimized settings. Actual results may vary depending on the printer and environmental conditions.
📊 Slicer Bridge Settings
Cura Settings
- Experimental > Enable Bridge Settings: Enable
- Bridge Wall Speed: 15-20 mm/s
- Bridge Skin Speed: 15-20 mm/s
- Bridge Fan Speed: 100%
- Bridge Skin Density: 100%
- Bridge Wall Flow: 95%
- Bridge Skin Flow: 90-95%
PrusaSlicer Settings
- Print Settings > Speed > Bridges: 15-25 mm/s
- Filament Settings > Fan speed > Bridges fan speed: 100%
- Print Settings > Advanced > Bridge flow ratio: 0.90-0.95
- Filament Settings > Cooling > Enable auto cooling: Enable
- Over bridges speed: 20 mm/s
OrcaSlicer Settings
- Quality > Bridge speed: 20-25 mm/s
- Quality > Bridge flow: 0.90-0.95
- Cooling > Bridge fan speed: 100%
- Quality > Internal bridge speed: 25-30 mm/s
- Quality > Internal bridge flow: 1.0
- Quality > Top surface bridge flow: 0.95-1.0
🧪 Bridge Test Model
You can use custom test models to test bridge quality.
Creating a Test Model:
- Search for "bridge test" on Thingiverse or Printables.
- Download a model that includes bridges at different distances.
- Recommended model sizes: 20mm, 40mm, 60mm, 80mm bridges.
- Change only one parameter per test.
Evaluation Criteria:
- ✅ No sagging, flat surface
- ✅ No stringing
- ✅ Good layer adhesion
- ⚠️ Slight sagging (acceptable)
- ❌ Significant sagging (adjustment needed)
- ❌ Bridge failure (serious issue)
🔄 Alternative Solutions
1. Support Structures
Use supports if the bridge distance is beyond the limit:
- Tree support: Fewer contact points, easy to remove.
- Normal support: More reliable but difficult to remove.
- Support interface: Flat surface between support and model.
2. Model Orientation
You can reduce bridging by rotating the model in a different direction:
- Rotating by 90° can eliminate the bridge.
- Align the bridge direction parallel to the fan direction.
- A short bridge is always better than a long bridge.
3. Splitting and Joining
You can split models that require long bridges in half and glue them together:
- Cut the model with Mesoslicer or 3D Builder.
- Print separately and join with super glue or epoxy.
🧵 Material-Based Bridge Performance
PLA - Best Bridging Material ⭐⭐⭐⭐⭐
- Fast solidification
- Low thermal expansion
- High bridge distance (80mm+)
- Responds very well to fan cooling
PETG - Moderate Performance ⭐⭐⭐
- Sticky texture can cause stringing during bridging
- Fan speed of 80-100% required
- Bridge distance lower than PLA (~55mm)
- High temperature sensitivity
ABS - Challenging but Possible ⭐⭐⭐
- Limited fan usage (risk of warping)
- Enclosed chamber provides an advantage
- Moderate bridge distance (~65mm)
- Can be corrected with post-processing
TPU - Most Challenging ⭐⭐
- Flexible nature increases sagging
- Requires very slow speed (10-15 mm/s)
- Short bridge distance (~40mm)
- Support usage is generally necessary
🖨️ Printer-Specific Notes
Bambu Lab (X1C, P1S, A1)
- Bridge settings are automatically optimized in Bambu Studio.
- X1C: Enclosed chamber is advantageous for ABS bridging.
- P1S: Aux fan improves bridge quality.
- A1: Single fan, pay attention to fan direction.
Creality (Ender 3, K1)
- Ender 3: Stock fan is usually insufficient, fan upgrade recommended.
- K1: Good bridge performance even at high speeds.
- Part cooling fan direction is critical.
Prusa (MK3S+, MK4, Mini)
- MK4: Excellent bridge performance, automatic settings are good.
- MK3S+: Fan duct upgrade improves bridging.
- PrusaSlicer bridge settings are generally optimized out of the box.
💡 Prevention Tips
- Optimize the fan first - It makes the biggest impact.
- Perform bridge tests - For every filament roll you have.
- Lower the temperature - By 5-15°C.
- Slow down the speed - In the range of 15-25 mm/s.
- Reduce the flow - By 5-10% (to 90-95%).
- Pay attention to fan direction - Should be parallel to the bridge direction.
- Prefer short bridges - With model rotation.
- Calibrate - Flow rate and e-steps.
❓ FAQ (Frequently Asked Questions)
What is the most important setting for bridging?
Fan speed is the most critical factor. Increasing fan speed to 100% often makes a big difference on its own. Temperature, speed, and flow rate follow in that order.
Why is PETG worse than PLA for bridging?
PETG's sticky texture and higher operating temperature slow down its cooling. Additionally, PETG's tendency to string can increase during bridging.
Is it always better to use supports instead of bridging?
No. For short bridges (under 30mm), using supports is a waste of material and time. Also, support removal can degrade surface quality. Optimizing bridging should always be the first choice.
How much does a fan upgrade improve bridging?
A quality part cooling fan (e.g., 5015 blower) can improve bridge quality by 30-50%, especially on printers with weak stock fans like the Ender 3.
Is retraction necessary during bridging?
Retraction usually doesn't occur during bridging because extrusion is continuous. However, retraction is important during travel moves before the bridge.