Bridging in 3D printing refers to building up a solid layer between two points, without any support from below. Since the material extruded in FDM printing is melted thermoplastic, it’s easy to understand that building perfect bridges can be challenging.
The easiest way to obtain perfect 3D printing bridging is by calibrating the settings with the help of a bridging test. In Cura, you can select from calibration shapes, customizable or automatic bridging tests, and even bridging torture tests, such as printing a double helix figure.
While calibration objects allow you to set the right parameters, you can further optimize bridging by adjusting the printing speed, printing temperature, and fan speed.
What Is Bridging In 3D Printing?
Bridging in 3D printing refers to creating a connection between two points vertically through a horizontal bridge. The width and thickness of the bridge may vary from model to model, but this function allows you to print a variety of hollow or decorative objects.
The trickiest part is figuring out the right extrusion temperature and cooling speed so that the filament can cool down fast enough to prevent sagging and oozing.
While bridging refers to building unsupported areas that remain suspended in the air, you must keep in mind that larger bridges typically require you to print some sort of supporting structure. This structure must then be removed through post-processing.
A way to prevent the use of supports is to change the orientation of the print – a model that requires long bridges when positioned horizontally will have significantly shorter bridges when printed vertically.
How To Setup Bridging
Knowing what bridging is in 3D printing is the first step to proper printer calibration. The method below refers to setting up bridging in Cura.
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1. Enable Bridge Settings in Cura
How challenging or easy it is to build bridges largely depends on the slicer program you’re using.
Ultimaker Cura is one of the most popular slicers – an open-source program that comes with a bunch of interesting features, including automatic bridge detection based on the model you’re slicing.
To detect bridges automatically, Cura asks users to enable bridge settings.
You can do this from the Experimental section. Go to the Custom mode and tick the box next to the Enable Bridge Settings.
If you can’t find this option, it may be hidden. You can modify the visibility from the Experimental section or via the menu bar. In the menu bar, open Settings and go to Visibility. Find the Enable Bridge Settings and set the option as visible.
2. Adjust Printing Parameters
When enabling the bridge settings in Cura, the slicer can detect bridges automatically and develop instructions for the printer to change certain parameters, such as the print speed, nozzle temperature, and fan speed, to prevent bridging problems.
However, anyone who has used a printer before, knows that automatic settings rarely match real-life conditions.
Things including the room temperature, the printer you’re using, the type of filament, filament brand and color, and other environmental factors can affect printing performance.
Defects are a lot more visible when printing bridges, because they are suspended in the air rather than on top of other solid layers.
The first parameter to adjust is the print speed. Perhaps the most challenging part is finding the right balance – you can’t print too fast, as the bridge may not stick well to pillars. At the same time, you can’t print too slowly because the printed material might sag.
Temperature is another essential factor. Lower temperatures are typically better for bridging, allowing the material to cool down faster. However, a too low temperature can increase the risk of poor adhesion to the pillars.
Experimentation is generally required to figure out the right print speed and temperature.
While the print speed can be adjusted in either direction (by increasing or diminishing it compared to the Cura suggestion), lowering the temperature by 5°C to 10°C is generally enough to improve the quality of bridges.
Another parameter to consider is cooling. Regardless of the material you’re using, the easiest way to prevent printing defects while printing bridges is by enabling the fan and setting its speed to 100%.
3. Test the Settings
When printing miniatures, you can test the settings by printing your final object and adjusting accordingly. However, if you’re working on larger parts, you might want to test the settings by running a test print.
Bridging print tests use various types of structures with shorter and longer bridges. These objects can help you evaluate the accuracy and quality of bridging at various lengths, and tweak the settings as needed until the results are satisfactory for the desired length.
There are various test structures that you can print, but if you don’t want to wrap your mind around finding the perfect test, you can download the Calibration Shapes plugin from Ultimaker.
This plugin can be found in the marketplace accessible from your Cura software and allows you to select the most appropriate structure to test the settings.
If you’re sure the print speed and cooling are just right, you can also test the temperature settings by printing a temperature tower instead of a bridging test structure.
These towers consist of identical bridges that are printed with the nozzle heated at various temperatures. This is the easiest way to figure out the right extrusion temperature for the material you’re using, as most tower files calibrate the nozzle temperature automatically.
After micro-adjusting the settings, you can check the results by printing a double helix structure. If you’re happy with the print, you can load your file and print the desired item.
Bridge Settings By Filament Type
Knowing how to set up bridging is key to perfect prints, but things are easier if you know where to start.
The table below shows the standard bridging settings for various FDM materials.
|PLA||180°C to 200°C||140 to 150mm/s||100%|
|ABS||210°C to 230°C||60 to 70mm/s||100%|
|PETG||225°C to 245°C||70 to 110mm/s||50% to 100%|
|TPU||200°C to 230°C||15 to 25mm/s||50% to 100%|
7 Tips To Fix Poor Bridges
Sometimes, your bridges may fail to achieve the desired quality, no matter how much you adjust the settings. These tips might help you out.
1. Decrease Build Plate Temperature
A common mistake when adjusting bridging settings is forgetting about the build plate temperature.
While this temperature shouldn’t affect bridging – heating the plate as required for the material you’re using is crucial to ensure bed adhesion – the truth is that it does.
A too hot build plate can improve adhesion, but it can also radiate heat onto the upper layers, contributing to oozing, sagging, stringing, and other bridging defects.
Similar to the nozzle temperature, the build plate temperature should be lowered by 5°C to 10°C.
2. Experiment with Different Settings
When enabling bridging, Cura adjusts the settings automatically – similar features are also available in other slicers. You can further adjust the parameters using the table above, but this might not guarantee good results from the start.
You should experiment with the settings and print test models to check how the material performs in your specific conditions.
If you’re concerned about wasting filament and energy, remember that test prints generally require few resources, but they could save you time and money in the long run.
If you have experimented with the settings already and found the ones that work, but your current print doesn’t have the desired quality, think about what changed.
A different filament – another color or a different brand – a change in the environmental conditions, and even a new model may require re-tweaking everything again.
3. Consider Object Orientation
As explained, the longer your bridges, the poorer the result. But improving print quality could be a matter of object positioning.
Things are simple – when designing an item, we tend to slice and print it in its natural position. This is the first instinct, as our brain needs to see the object as it is to figure out whether it’s what we need.
However, thinking out of the box and printing a horizontal object vertically, for instance, can reduce the size of the bridges your printer has to make.
In this case, the printer would extrude the bridges as vertical pillars, whereas the object’s true pillars would be printed as bridges.
Once the project is complete, all you have to do is smooth out the side and flip it in the right position.
While flipping a horizontal item to a vertical printing position is the most straightforward orientation adjustment, there are many other ways to reposition an object.
You can do this after loading the design in the slicer software, before hitting the slice button.
4. Decrease Extrusion Multiplier
Extrusion multiplier in 3D printing is a setting that determines the rate at which filament is extruded. A too high extrusion multiplier can increase the risk of oozing, even more so if you’re printing bridges.
As the excess filament pushes down on the bridge, it could lead to sagging, breaking, and other types of bridge failures.
Lowering this number by a small amount – usually no more than 10% from the default number set by your slicer – might solve the issue.
5. Buy Quality Filament
It goes without saying that one of the main factors that can affect print quality is the quality of the filament you’re using.
Choosing renowned brands might cost you more upfront, but it can increase bridging quality. This means less wasted material and optimized energy consumption, which could actually save you money in the long run.
6. Dry Filament Before Printing
Another factor to consider before correcting other bridging parameters is the quantity of moisture in your filament.
With very few exceptions, all FDM filaments are hygroscopic. They absorb moisture from the environment and, if they are not dried before printing, they could lead to a variety of printing defects.
All filament types can be dried in a filament drier or in the kitchen oven. If you decide to dry filament in an oven, check the temperature specifics and average drying times for your specific filament type.
7. Add Supports
When all fails, a way to prevent bridging defects is by adding supports.
It might feel like cheating – and may result in more laborious post-processing – but you may find that all your bridges turn out just right.
Building high-quality bridges in 3D printing can be challenging, but the results are usually satisfactory once you figure out the right settings. Changing the object position on the build plate and using supports might help in the case of long bridges. Using quality filament and drying it before printing can improve the overall quality of your print.