Why is my petg stringing?
Quick Answer
PETG stringing primarily occurs due to incorrect retraction settings, excessive printing temperature, or moisture in the filament. Adjusting retraction distance to 6-8 mm at 40-60 mm/s for Bowden setups, lowering nozzle temperature by 5-10°C increments, and drying filament at 60°C for 4-6 hours are immediate steps to reduce stringing.
Understanding PETG Stringing
PETG filament is inherently more prone to stringing compared to other materials like PLA due to its unique material properties. It has a higher viscosity when molten and a natural tendency to stick to itself and the nozzle, which means it easily oozes out during non-printing moves. This oozing creates fine plastic strands, or 'strings,' between printed parts as the print head travels from one point to another.
This phenomenon is exacerbated by several factors. High printing temperatures keep the PETG in a more fluid state for longer, increasing its ability to flow and string. Inadequate retraction settings fail to pull enough molten plastic back into the nozzle to relieve pressure, allowing it to drip. Furthermore, PETG is hygroscopic, meaning it readily absorbs moisture from the air, and wet filament boils internally during printing, causing micro-explosions that push molten plastic out of the nozzle, leading to severe stringing and poor print quality.
How to Fix PETG Stringing Specifically
First, calibrate your retraction settings precisely. For Bowden extruders like those on a Creality Ender 3 or Anycubic Mega S, begin with a retraction distance of 6-8 mm and a retraction speed of 40-60 mm/s. For direct drive extruders such as a Prusa MK3S, start with a much shorter distance, typically 0.8-1.5 mm, at the same 40-60 mm/s speed. Print a retraction tower test model, typically found on Thingiverse, to fine-tune these values in 0.5 mm distance increments or 5 mm/s speed increments to find the optimal balance.
Then, optimize your printing temperature. While PETG typically prints between 220-250°C, starting at the lower end of this range, around 230°C, often reduces stringing. Print a temperature tower calibration model, decreasing the nozzle temperature by 5°C for each section, starting from 250°C down to 220°C. Observe which temperature section exhibits the least stringing and best layer adhesion. Adjust your slicer's nozzle temperature setting to this optimized value.
Next, ensure your PETG filament is dry. PETG absorbs moisture quickly, even if stored in a sealed bag. Place your filament roll in a dedicated filament dryer at 60-65°C for 4-6 hours, or use a convection oven set to 60°C for 4 hours (ensure the oven maintains a stable temperature and doesn't overshoot, as higher temperatures can melt the spool). Printing with dry filament significantly reduces stringing, bubbling, and improves overall print strength.
Finally, adjust your travel and print speeds. Increase your non-print travel speed to 120-150 mm/s. Faster travel minimizes the time the nozzle spends moving between features, giving less opportunity for molten PETG to ooze. Simultaneously, consider slightly reducing your overall print speed to 40-50 mm/s for better control and adhesion, especially for perimeters. Also, experiment with enabling Z-hop or Z-lift in your slicer, setting it to 0.2-0.4 mm. This lifts the nozzle slightly during travel moves, preventing it from dragging across the print and potentially pulling strings.
Common Mistakes to Avoid
One frequent error is assuming new PETG filament is dry. Many users open a fresh spool and immediately start printing, only to encounter stringing. This happens because PETG is highly hygroscopic and can absorb significant moisture during manufacturing, shipping, or storage before it even reaches you. To avoid this, always dry new PETG filament for at least 4 hours at 60°C using a filament dryer or a convection oven before its first use.
Another common mistake is setting excessive retraction distances or speeds, particularly with Bowden setups, in an attempt to completely eliminate stringing. Pushing retraction distance too high (e.g., beyond 8 mm for Bowden) or speed too fast (e.g., above 70 mm/s) can lead to filament grinding by the extruder gear, heat creep causing clogs in the hotend, or even wear on the filament itself. To prevent this, stick within the recommended ranges of 6-8 mm distance and 40-60 mm/s speed for Bowden systems, and 0.8-1.5 mm distance for direct drive systems, and fine-tune gradually with test prints.
A third mistake involves neglecting proper temperature calibration. Many users print PETG at the higher end of the recommended temperature range (e.g., 245°C) without performing a temperature tower calibration. While some PETG brands may require higher temperatures, printing too hot keeps the material excessively fluid, making stringing much worse. Always print a temperature tower to identify the lowest possible printing temperature (typically 225-235°C for most PETG) that still provides good layer adhesion and part strength, as this significantly reduces oozing.
Expert Tips for Best Results
Employ a silicone sock on your hotend block to maintain stable temperature and prevent molten PETG from adhering to the heater block. This small silicone cover, costing around $5, insulates the hotend, reducing temperature fluctuations that can contribute to inconsistent oozing, and keeps the block clean, preventing plastic buildup that could drag across the print and cause strings.
Increase your non-print travel speed significantly, aiming for 120-150 mm/s in your slicer settings. The benefit of faster travel is that it minimizes the duration the nozzle spends moving between different parts of your print, thereby reducing the window of opportunity for molten PETG to ooze out and create strings. This is especially effective when combined with optimized retraction settings.
Enable the 'Wipe' setting in your slicer, typically set to 1-2 mm. This feature causes the nozzle to slightly wipe over the last printed perimeter before retracting and traveling to the next print area. This action helps to clean any small glob of plastic from the nozzle tip, preventing it from being carried over and deposited as a string on another part of your print. It's a subtle but effective way to minimize residual oozing.
Consider printing PETG within an enclosure, even a simple DIY one made from a cardboard box. While PETG is less sensitive to drafts than ABS, a stable ambient temperature within an enclosure (around 30-40°C) reduces thermal fluctuations at the print area. This helps the molten plastic maintain a more consistent viscosity, making retraction more effective and reducing the likelihood of uncontrolled oozing and stringing.
Frequently Asked Questions
What retraction settings are best for PETG on an Ender 3?
For an Ender 3 with its Bowden extruder, start with a retraction distance of 6-8 mm and a retraction speed of 40-60 mm/s. Print a retraction tower test and adjust in 0.5 mm distance increments or 5 mm/s speed increments to fine-tune for your specific filament and setup.
How do I know if my PETG filament is wet?
Wet PETG filament will often produce popping or sizzling sounds during printing, caused by trapped moisture rapidly expanding into steam. You'll also observe inconsistent extrusion, excessive stringing, poor layer adhesion, and a rough, bubbly surface finish on your prints. Dry your filament at 60°C for 4-6 hours to confirm.
Can a worn nozzle cause PETG stringing?
Yes, a worn or damaged nozzle can contribute to PETG stringing. An oval or enlarged nozzle opening, or internal rough spots, can prevent clean filament cutoff after retraction, leading to increased oozing. Replace your brass nozzle after 100-200 hours of printing PETG, or consider a hardened steel nozzle for longer life.
Should I use Z-hop for PETG to prevent stringing?
Enabling Z-hop (0.2-0.4 mm) in your slicer can help reduce PETG stringing by lifting the nozzle slightly off the print surface during travel moves. This prevents the nozzle from dragging through already printed plastic, which can pull up strings or knock over delicate features. Test it with your specific print to ensure it doesn't introduce other issues like visible Z-seams.
What is the ideal bed temperature for PETG to reduce stringing?
The bed temperature for PETG typically ranges from 70-90°C. While bed temperature primarily affects adhesion, a slightly lower bed temperature (e.g., 70°C) can sometimes indirectly reduce stringing by promoting faster cooling of the initial layers, but the nozzle temperature and retraction settings are far more critical for addressing stringing directly.