How to Improve PETG Bridging? (And Print Perfect Bridges)

When taking up 3D printing as a hobby, one of the best things you can do is accept that facing and resolving issues is half the fun, as the pursuit to achieving the perfect is a never-ending one with many obstacles in the way.

Among all the issues, issues related to bridging have always been some of the trickiest in 3D printing, as even a single parameter that you haven’t configured as optimally as possible can contribute to bridging-related issues, with bridges drooping the most common one.

As the optimization process you should perform depends on the filament you use, today’s topic will be improving bridging while printing with PETG filament in particular, where we have noticed that many members of the community have trouble.

So, how to improve PETG bridging and print perfect bridges every time?

Here is a list of things we recommend doing to improve bridges while printing with PETG filament:

  • Decrease the print temperature
  • Adjust the print speed
  • Increase the cooling speed
  • Decrease the flow rate
  • Rotate your model to reduce the number of bridges if possible
  • Use supports for printing bridges

In the upcoming section, we will go into more detail about each of these items, where we will discuss their effects on printing bridges, point out the signs you should be looking out for, and share our recommendations for the values you should use.

How to Improve PETG Bridging?

As poor bridging can occur due to many factors, we believe that taking a deep look separately at each is the best course of action to improve bridging with PETG.

Decrease the Print Temperature

A print temperature that is too high can cause PETG to take way too long to cool down, which will eventually cause it to droop as the plastic does not have any support beneath it in the case of bridges.

While the exact temperature you should use is dependant on the brand of PETG you’re using, we recommend going for a bridge print temperature that is 10 to 20 degrees Celsius lower than the actual print temperature.

For instance, if you’re printing PETG with a nozzle temperature of 230 degrees Celsius, using a nozzle temperature of 210 degrees Celsius for bridges will yield better results.

As an excessive print temperature is perhaps the factor that is most likely to cause bridges to droop, it should be the first thing that comes to mind.

Adjust the Print Speed

A print speed value that is too high will cause adhesion issues in your bridge due to layers not having enough time to cool down.

On the other hand, a print speed value that is too low can cause your bridge to droop due to the filament not being extruded quickly enough.

In most cases, a low print speed rather than a high print speed is the problem, as a print speed that is too high would also cause adhesion issues in other parts of the model.

As a result, the solution is to increase the print speed for bridges with a value in the range of 10 to 15 mm/s by using the parameter that modifies the print speed for bridges but not the other parts of the model.

For instance, you can use the Bridge Skin Speed and Bridge Wall Speed parameters in Cura to adjust the print speed for bridges and input a value that is 10-15 mm/s higher than the standard print speed you use for PETG.

Increase the Cooling Speed

A low cooling speed value will cause the PETG to stay molten for too long, and due to the molten plastic not having any support, it will start weighing down and drooping.

Even though you will hear many sources telling you to disable fans while printing PETG, they often forget to mention that you should turn them back on for bridges.

We recommend setting the fan speed to 100% for bridges and reducing it in 5% increments if you notice issues related to layer adhesion due to excessive cooling.

As a rule of thumb, try to keep the cooling speed as high as possible at the point where you don’t face issues with layer adhesion or clogging of the nozzle for the best surface resolution with PETG.

Decrease the Extrusion Multiplier (Flow Rate)

A wrongly set extrusion multiplier value can easily cause over-extrusion, which will quickly destroy a bridge due to the amount of plastic being way too much.

As the flow rate is a sensitive setting, we recommend reducing it in increments of 1% for bridges until over-extrusion isn’t a problem anymore.

For instance, you will find that the flow rate is set to 100% by default in Cura, and you can reduce the flow rate for bridges and experiment until you find the optimal values with the Bridge Wall Flow and Bridge Skin Flow parameters.

Rotate the Model

As bridges (and overhangs) are always problematic to print to some extent, avoiding them is the best course of action if you have the chance.

While a solution that is often overlooked, rotating the model can allow you to reduce, or in some cases, completely get rid of the bridges, making the printing process a whole lot easier.

If you cannot reduce the number of bridges, reducing the distance is also quite helpful. As long bridges are much harder to print than short ones, you will make the process smoother with bridges that aren’t too long.

Even though this isn’t always a solution, as it’s impossible to eliminate, reduce, or shorten bridges in some models no matter how you rotate them, it’s a practical trick to remember.

Use Supports

The primary issue that causes bridges to be hard-to-print is that they don’t have any foundation between them as opposed to regular parts that have contact with the build plate.

Adding supports to the bridges in your model allows you to print bridges more stably as they connect the bridges to the build plate, allowing the bridges to have a foundation, similar to other parts of the print.

While supports create a small amount of extra work as you will need to remove them after the printing process is over, there is no denying that they make the process of printing bridges much smoother.

Is PETG Good at Bridging?

With each type of filament having different properties, it’s no secret that one can perform better than the other while printing bridges, which again reminds us of the importance of filament selection for a project.

As PETG is able to maintain its shape at higher temperatures compared to another popular filament type, such as PLA, we can indeed consider PETG to be good at bridging to an extent.

While you can indeed print perfect bridges with any filament if you get the configuration correct, there is nothing wrong with getting help from the filament’s own qualities to make the process smoother.

Wrapping Up

While improving your PETG bridges will take some time and effort due to the existence of many factors that can contribute to poor bridging, it’s definitely a solvable issue as long as you follow the correct steps.

To quickly recap, here are the things we recommend doing to improve PETG bridging:

  • Decreasing the extruder temperature
  • Adjusting the printing speed
  • Increasing the cooling speed
  • Decreasing the extrusion multiplier
  • Rotating the model to avoid bridges whenever possible
  • Using supports

As experimentation is vital to print the best bridges possible, being patient while optimizing the settings will be your best asset in this journey, so remember not to give up!