Why Is Infill Not Sticking While Printing with PETG? (How to Fix?)

Until the 3D printing technology evolves to a point where we will have access to 3D printers that can configure themselves automatically depending on the model we are printing and the filament we are using, we need to accept that the process of troubleshooting is essential to 3D printing.

On the other hand, the good news is that troubleshooting most 3D printing problems happen at the software level, where slight improvements to the print settings can resolve critical issues that cause the 3D printing process to fail entirely.

Today, our topic will be the specific issue where the infill of the model does not stick to the rest of the object while printing with PETG filament, a problem that requires fixing as soon as possible for the 3D printing process to be successful.

So, what can cause infill not to stick while printing with PETG?

Below, we have listed the factors that can prevent the infill from correctly sticking to the walls while printing with PETG:

  • Too high printing/infill speed
  • Too low printing temperature
  • Too low line width/infill line width
  • Too much cooling
  • Incorrect filament diameter
  • Extruder problems

Next up, we will go into the reasons that can cause infill not to stick while printing with PETG in more detail, find out what we can do to fix this problem as efficiently as possible, and take a look at the signs that will help us identify the issue of infill not sticking.

Why Is Infill Not Sticking While Printing with PETG? 

Finding the culprit behind the issue of infill not sticking is a tricky one no matter the filament you’re printing with, as even getting one of the print settings slightly wrong can cause this problem and make your prints fail.

Too High Printing/Infill Speed

The printing (or infill) speed parameter controls how quickly the 3D printer extrudes the infill, playing a vital role in the formation of the infill.

When the printing speed is way too high, the extruder may have difficulties keeping up with the amount of PETG required to proceed with the printing process optimally (especially if the printing temperature is low), which causes under-extrusion.

Under-extrusion during the printing of the infill then leads to the infill not sticking to the walls correctly, as the actual amount of plastic that goes into the infill ends up being way less than the intended amount, creating gaps.

Too Low Printing Temperature

The printing temperature determines how hot the plastic gets during the printing process, which also applies to the infill.

When the printing temperature is way too low, PETG may not reach a point where it flows freely out of the nozzle, causing under-extrusion due to the actual amount of PETG coming out being much less than calculated.

As a result of this issue happening during the infill’s printing, the infill’s chance of not sticking to the walls becomes pretty high since the lack of PETG will cause gaps to appear between the infill and the walls.

Too Low Line Width/Infill Line Width

The line width (or the infill line width) determines the horizontal thickness of each infill line the 3D printer extrudes.

When the line width (or the infill line width) is lower than it should be, the print lines that come out of the nozzle become way too thin, to the point where the infill doesn’t get enough PETG to form a strong structure.

This weakness in the infill prevents the infill and the walls from connecting to each other, causing the issue of the infill not sticking.

Too Much Cooling

The cooling fan speed determines how quickly the cooling fans spin, which directly reduces the time required for the infill to solidify from its melted state.

Too much cooling will cause PETG to solidify way earlier than it should, and in the case of the infill, this can happen before the infill starts forming strong bonds with the walls of the model.

As a result of these bonds not being formed, the walls and the infill will separate.

Incorrect Filament Diameter

The filament diameter parameter allows the 3D printer to know the diameter of the filament you’re using, which it uses to calculate how much filament needs to go through at any given point.

When the filament diameter in the slicer doesn’t match the actual diameter of the filament, under-extrusion will occur (in the case where the slicer value is higher than the real value) due to the printer miscalculating the amount of PETG going through the extruder.

As a result, the infill doesn’t receive enough plastic, creating gaps between the walls and the infill.

Extruder Problems

The extruder assembly is responsible for pushing the filament out of the nozzle in a consistent manner that matches the calculations of the slicer software.

An issue with any part of the extruder, from a clogged nozzle to faulty gears, can instantly cause under-extrusion and cause the infill to have less PETG than it requires.

Once again, the lack of material in the infill will prevent it from correctly connecting to the walls.

How to Fix Infill Not Sticking While Printing with PETG?

Resolving the infill not sticking issue can be a slightly complicated process due to the number of potential factors that can cause the problem, meaning that you will most likely need to spend some time and effort on this.

Below, we have listed the solutions we recommend applying to fix the issue of infill not sticking while printing with PETG:

  • Decrease the printing or infill speed. This way, the 3D printer will be able to extrude the calculated amount of plastic consistently, ensuring that the infill has enough material to connect to the walls. A range of 40 to 60 mm/s is acceptable for printing PETG.
  • Increase the printing temperature. Setting the printing temperature to the filament manufacturer’s specifications will always yield the best results, but if you aren’t following these instructions, experimenting with slight (5 degrees at a time) increases can be helpful.
  • Increase the line width or the infill line width value. The line width value should be no less than 60% of the nozzle size, but we recommend using a number between 100% and 120% of the nozzle size for best results.
  • Decrease the cooling fan speed. It’s possible to print PETG with minimal to no cooling, and going for a lower cooling fan speed value will ensure that the infill has enough time to bond with the walls.
  • Ensure that the filament diameter value is correct. The filament diameter value in the slicer settings needs to match the diameter of the filament you’re using. For best results, we recommend measuring the filament with calipers.
  • Ensure that the extruder is operating correctly. As the extruder contains many parts that can cause the whole thing to fall apart, a thorough inspection (checking for a clogged nozzle, faulty motor, worn-out gears, etc.) is best.
  • Increase the infill overlap or infill overlap percentage value. The infill overlap parameter instructs the 3D printer to print the infill and the walls in a way where they overlap, which can quickly fix the issue by ensuring that the walls and the infill connect. The value you specify for this parameter will determine how deep into the walls the infill will be.
  • Increase the flow rate value. While this is more of a quick and dirty fix with the potential to cause other problems, increasing the flow rate value in small increments can be helpful to close out minor gaps in the infill and get it to stick to the walls.

How to Identify the Issue of Infill Not Sticking While Printing with PETG?

Having an idea of the signs to look out for to identify the issue of infill not sticking is a step in the right direction to resolve the problem, as the first step to applying the correct solution is to pinpoint the issue.

The easiest way to identify the issue of infill not sticking while printing with PETG is to observe the printing process as the 3D printer extrudes the infill of the model since you will be able to spot the gaps between the walls of the model and the infill quickly.

In a scenario with no issues, the walls and the infill should seamlessly integrate without any gaps, forming a uniform structure where you shouldn’t be able to tell where the walls end and where the infill starts.

As the issue of infill not sticking to the walls is a serious threat to the model’s structural integrity, fixing the problem will be necessary for a successful print in this case.

Wrapping Up

As the issue of infill refusing to stick to the rest of the model while printing with PETG can entirely ruin the printing process and require you to start over, it’s vital to identify the issue as early as possible and take the appropriate action for fixing it quickly.

To quickly recap, most of the factors that can prevent infill from sticking with PETG are under-extrusion related, such as too high printing speed, too low printing temperature, too low line width, incorrect filament diameter, and issues with the extruder assembly, with too much cooling being one factor that isn’t directly related to under-extrusion.

While going through the factors we have listed above and applying the necessary corrections is the best way forward, a quick fix is also possible by modifying the infill overlap and flow rate parameters in Cura, especially in minor cases where you don’t want to tinker with the rest of the parameters too much.

Happy printing!