PETG (Polyethylene terephthalate glycol-modified) is a versatile thermoplastic material that is widely used in 3D printing. PETG offers excellent strength, durability, and flexibility, making it an ideal material for producing functional and aesthetic parts. However, one common issue that arises during PETG 3D printing is stringing.
This article aims to offer a complete guide on the topic of PETG stringing, covering its causes, effects, and strategies to prevent it.
What is PETG Stringing?
PETG stringing occurs when melted PETG material forms thin, filamentous strands during 3D printing. These strands often appear between two or more distinct parts of a printed object, resulting in a web-like structure that can be visually unappealing and negatively impact the part’s performance.
Why does PETG Stringing Occur?
Several factors contribute to stringing, including temperature, retraction settings, and nozzle size. Firstly, if the extruder’s temperature is too high, the PETG material becomes more fluid, making it easier for the melted material to travel and form strings between parts.
Secondly, the retraction settings play a crucial role in preventing the stringing of PETG. Retraction involves removing the filament from the nozzle while moving between different print sections.
If the retraction settings are too low, the melted material will continue to flow out of the nozzle, causing stringing. Lastly, the nozzle size can also affect stringing. Smaller nozzle sizes produce thinner strings that are more difficult to remove and can accumulate over time.
How to Identify Stringing
Detecting stringing is typically straightforward. When features are spaced too far apart, thin plastic strands similar to cobwebs or hairs will be visible on the printed object.
One can determine the severity of the stringing issue by printing a stringing test print or stringing tower. This simple STL model (such as this) is purposely designed to showcase stringing. Printing this model can help determine whether adjustments to certain print settings can alleviate the problem.
How To Prevent PETG?
Thankfully, there are numerous practical approaches for mitigating PETG stringing. Below are some of the most commonly used solutions: stringing?
Adjust Retraction Settings
Retraction is a crucial feature of FDM 3D printers that involves the nozzle pulling back a small amount of filament before moving to a new location. Its primary purpose is to prevent oozing and stringing, making it essential to set the appropriate retraction parameters for successful PETG printing, mainly when using a Bowden extruder instead of a direct-drive extruder.
There are four primary parameters to focus on when adjusting retraction settings to reduce stringing:
Retraction distance: Increasing the retraction distance is one way to minimize PETG stringing. This involves retracting a more extended section of filament before the printhead moves. You can try increasing the distance in increments of 1 mm and observe the effect using a stringing tower.
Retraction speed: Another way to minimize the stringing of PETG is by increasing the retraction speed, i.e., quickly retracting the small portion of the filament. You can try increasing the retraction speed in increments of 5 mm/s.
Minimum travel distance: Stringing in PETG is more likely to occur over long travel distances, such as when the printhead jumps along the X or Y axes. Your default settings may not allow for retraction over smaller distances. Consider reducing the minimum travel distance so that retraction occurs even for small jumps.
Vertical lift: Disabling the Z-Hop feature of the Cura slicer application, which instructs the printhead to move vertically (along the Z axis) during travel to avoid dragging on the part’s surface, can reduce PETG stringing.
Decrease the Nozzle Temperature
If adjusting retraction settings fails to reduce PETG stringing, the next step is to decrease the temperature of the printer’s nozzle. Excessive heat can cause filaments to ooze uncontrollably, even with proper retraction and travel settings.
Consider printing a temperature calibration block or a temperature tower to fine-tune the temperature. These models provide instructions for finding the optimal nozzle temperature in a single test. However, avoid prioritizing eliminating stringing over achieving a smooth surface finish.
Keep the PETG Filament Dry
Moisture can trigger stringing in any plastic material. This is because humidity generates tiny air pockets in the filament, which burst when heated. When the nozzle is in motion, this bursting can cause the molten filament to leak out, resulting in stringing.
Since PETG is particularly susceptible to stringing, keeping PETG filament spools dry is critical. This can be achieved by storing them in an airtight container with a desiccant, using a filament dryer, or gently warming them in an oven before printing.
Adjust Nozzle Temperature
PETG extrusion typically requires a high-temperature nozzle to ensure good material flow and layer adhesion. According to our research, the recommended extrusion temperature for PETG is around 245 °C. However, excessive temperatures and highly fluid material can lead to stringing.
To address stringing when printing with PETG, try gradually reducing the printing temperature in increments of 5 °C. This can help to minimize stringing without negatively impacting the quality or durability of the print or causing clogs or adhesion issues (such as poor adhesion of the first layer). Increasing the cooling fan speed can also help to cool the PETG as it leaves the nozzle.
Slow the Printing Speed
The print speed of a 3D printer refers to the rate at which the print head moves during printing. Slower print speeds typically improve print quality because the printer has more time to extrude the material accurately. Conversely, faster print speeds can make it difficult for the printer to extrude and place the melted filament precisely.
However, if you’re experiencing PETG stringing or blobbing issues, increasing the print speed may help. Slow print speeds can leave the extruder in the exact location for an extended period, leading to unintentional filament leakage. PETG filament usually produces the best results at speeds between 40-60 mm/s. While it’s essential to experiment with your settings to find superior print speed, it shouldn’t be your primary concern for stringing issues.
While faster print speeds can help reduce stringing, they can cause other issues. Generally, it’s best not to exceed a print speed of 60 mm/s when printing PETG. First, adjust your temperature and retraction settings, as these usually provide the most significant improvements.
Adjust Travel Speed
Your printer’s travel speed refers to how fast the nozzle moves when it’s not printing. During these movements, called “travel moves,” your printer won’t actively extrude material. The excess filament may ooze out and cause stringing if your travel speed is too slow.
To prevent stringing, it’s recommended to increase your travel speed. PETG filaments work well with any travel speed, and faster speeds reduce the amount of time the extruder is hanging over open air.
If you have a rigid 3D printer with little moving mass, you can print at 200 mm/s or higher travel speeds. However, open-frame budget 3D printers are often limited to travel speeds of 100 mm/s or less, and higher speeds may result in visual artifacts.
Fortunately, you can set your travel speed faster than your print speed without sacrificing print quality. This is because it only affects the areas between print sections. Once the nozzle reaches the next part of your print, it will return to moving at your print speed.
PETG filament is a popular material for 3D printing due to its durability and strength. However, PETG stringing can be a frustrating problem to deal with. By adjusting settings such as temperature, retraction, print speed, and travel speed, and you can minimize stringing and achieve high-quality prints.
Experimenting with different settings is essential to find the optimal balance between stringing reduction and print quality. With these tips and patience, you can overcome stringing and create successful 3D prints with this versatile filament.