Messy bridges are endlessly frustrating for beginner and veteran 3D print makers alike. These easy fixes can help you get perfect bridges for every print.
What is bridging?
Owing to the nature of 3D printing, pieces of printed models that are much higher than the base of the print and overhangs require additional support. Bridging refers to the extrusion of material that horizontally supports two raised points. Bridging problems are extremely common and relatively easy to address by adjusting basic print settings.
Test your bridging capacity
Before tweaking your printer settings, you have to identify exactly how well your printer makes bridges. We recommend the Bridging Test, which is a simple, customizable test print that allows you to easily identify consistency and evenness issues in your bridges. It will also how you which lengths cause problems for your printer. Most people can effectively and reliably print 50–100 mm bridges. With optimal settings, you can get 150+ mm bridges, which is a huge plus for makers who routinely print larger objects.
Check the cooling settings
The first setting to adjust when attempting to fix poor bridging performance is print cooling or print fan speed. Because bridges need to quickly connect two points of the print, a longer setting time will lead to drooping or breakage. Set your fan speed to 100% and run the test print again. If your fan speed is already at 100%, adjust it in 5% increments until you get clean and solid bridges.
Take care not to over-adjust your fan speed. If your print cools too quickly, your layer adhesion may suffer, or you may experience lamination in larger prints as portions of the print cool much more quickly than others. If this begins to happen before your bridges are fixed, adjust the fan speed to the point at which you get good adhesion and drying and move on to the next fix.
Decrease the flow rate
Flow rate is another crucial factor affecting bridge quality; like fan speed, flow rate affects how quickly bridges set. If too much molten filament is deposited at once, it will not be able to set fully before the next layer is printed, which can also lead to sagging.
Decrease your flow rate or extrusion multiplier in your slicer by a small increment. Run the test print to identify whether this has improved the setting of your bridges.
Decrease the nozzle temperature
The nozzle temperature can impact how filament flows in a manner that is very similar to your flow rate setting. An overly hot nozzle can lead to too much filament being extruded at once, which can produce messy edges and bridges.
To determine which nozzle temperature is best for the filament you are working with and the bridges you are trying to use, we recommend the modified customizable temperature tower test. This version of the well-known temperature tower includes a point mounted on an overhang at each level, which can ensure that the proper temperature settings are used for both bridging and print details.
To test various temperatures, you need to adjust the g-code to ensure that the temperature changes at each tested height. The process outlined below is for Cura:
Select ‘Extensions’ > ‘Post processing’ > ‘Modify g-code.’ Then, add the ‘Vary Temp With Height’ plugin.
Here, you can input the height increment to determine how often the printer should increase the temperature and the temperature increment. The linked Thingiverse model includes the necessary code for both Cura and Slic3r in the Thing Details.
Decrease the print speed
Overly high print speeds can also affect bridge quality. If the nozzle moves too fast, the filament will be unable to adhere to the previous layer or bridge points, leading to stringy and unstable bridges.
Decrease your print speed by 10 mm/sec increments. Like mentioned above, it is important to use small increments to ensure that you do not overcorrect your print settings. Take care not to reduce the print speed too much. If the print speed is too slow, the filament will be suspended in the air for too long, causing drooping or poor setting.
Adjust your model orientation
Some models may not require all this fine-tuning; instead, play around with the model orientation and try to eliminate bridges. Even if you cannot eliminate all the bridges in the model, you may be able to adjust the model orientation to reduce the longer bridges and stay within the good-quality bridge range you identified in your initial bridging test.
💡 Do not forget the 45° rule: If an overhang on your model exceeds 45°, you will need supports.
Add supports to reduce or eliminate bridges
Supports add post-processing time but can mitigate or completely remove the stress of fine-tuning your bridging settings. The number and type of supports you can use will be heavily impacted by your model design.
Note that some models, such as highly complex figures, may not allow for supports to be easily removed. Have needle-nose pliers and a sharp hobby knife ready to cut away smaller supports as close to the print surface as possible. Some 3D print marketplaces sell 3D printing–specific cutting tools for easy removal. Be ready to sand down the remnants of the supports to yield a perfectly smooth final print.