You’ve chosen PETG for your 3D printing project, drawn in by its strength, impact resistance, and flexibility. It’s the go-to material for mechanical parts, plus it’s affordable and boasts impressive chemical and moisture resistance.
But there’s a catch: PETG stringing. Those pesky hair-width strands that trail from your print head can turn a promising project into a sticky mess. If you’re tired of dealing with the frustration of filament oozing and stringing, you’re not alone. Let’s dive into the world of PETG and unravel the mystery of stringing once and for all.
What is PETG Stringing?
PETG stringing occurs when your printer head extrudes filament over open spaces during travel movements. Imagine it like a hot glue gun that drips even after you’ve stopped squeezing the trigger. The result is thin strands of plastic—similar to cobwebs—that can ruin the aesthetics and precision of your prints.
There are multiple causes of PETG stringing, including high print temperature, fast print speeds, and incorrect retraction settings.
How to Prevent PETG Stringing
PETG stringing can detract from the quality of your 3D-printed objects. Here are some tried and true methods to prevent PETG stringing.
1. Enable Retraction Settings
Retraction is the process of the printer’s extruder pulling the filament back away from the nozzle when the nozzle is moving over an air gap.
When a 3D printer moves the print head between different areas of the print, the melted filament can ooze out of the nozzle, leading to unwanted strings and blobs. Retraction works by slightly pulling the filament when the print head moves but not actively printing to prevent unwanted extrusion.
If you’re struggling with stringing, enabling retraction should be your first step.
In Curas slicing software, the retraction section has two main settings: Retraction Speed and Retraction Distance.
The retraction speed refers to how quickly the extruder motor pulls the filament away from the nozzle when the nozzle is moving over an air gap.
You can reduce stringing by increasing the retraction speed. A faster speed quickly reduces pressure in the print head and prevents unwanted filament extraction.
Here are the ideal PETG retraction settings based on my experience working with over 30 3D printers :
- For Bowden tube 3D Printers
- Retraction Distance: 6 mm
- Retraction Speed: 40 mm/s
- For Direct Drive 3D Printers
- Retraction Distance: 1.5 mm
- Retraction Speed: 35 mm/s
It’s essential to find the right balance. Too little retraction won’t prevent stringing, while too much leads to other issues like under-extrusion or even filament grinding. PETG filament is more sensitive to over-retraction than PLA. Be very careful not to increase the retraction distance too much.
If you find retraction isn’t enabled over small gaps, you can adjust the minimum distance required to enable retraction by changing the “minimum travel distance.”
2. Decrease Print Temperature
One of the best ways to fix PETG stringing is to decrease your printer’s nozzle temperature.
A relatively high temperature produces a more liquid (or viscous) filament. When the filament is overheated, it becomes more fluid and thus more prone to oozing and stringing as the print head moves around.
The key to finding the optimal temperature is to start with the lower end of the recommended temperature range for your specific PETG filament. The manufacturer’s recommended print temperature is on the filament packaging or spool.
If you can’t find the manufacturer’s recommendation, we get the best results with PETG using a nozzle temperature between 235°C and 250°C.
Increase the temperature in 5°C increments until you find the right print temperature.
By fine-tuning the print temperature, you can achieve a balance where the PETG is hot enough to adhere properly between layers but cool enough to reduce stringing.
Editor’s Note
You can also print the temperature tower calibration test from Thingiverse to quickly find the best temperature for printing PETG. The temperature tower is our preferred calibration method because it shows stringing and surface details in 5-10°C increments.
3. Increase Travel Speed
Travel speed is the speed at which the print head moves over open spaces. Increasing the travel speed minimizes the nozzle’s time moving over non-print areas.
When the travel speed is too slow, the hot end lingers over parts of the print, giving the molten PETG more time to ooze out of the nozzle. This ooze can form strings as the print head moves to the next point. Increasing the travel speed makes the print head move more quickly between points, leaving less time for the filament to leak out and form strings.
However, it’s essential to find a balance.
If the travel speed is set too high, it might lead to other issues. For instance, the printer might not be able to accurately follow the intended path at very high speeds, especially on printers with less rigid frames. Excessive speeds lead to reduced print quality and inaccuracies in the dimensions of your printed object.
We find that the optimal travel speed is 150mm/s. Other makers have gone as high as 200mm/s without any problems.
4. Dry Your Filament
Drying your filament is essential in preventing PETG stringing during 3D printing. PETG filament is hygroscopic, meaning it absorbs moisture from the air.
Absorbed moisture wreaks havoc during printing as it turns to steam in the 3D printer’s hot end. The steam creates pressure that forces excess material from the nozzle, leading to stringing and other issues like zits and blobs.
If you suspect your filament is wet, dry your PETG filament with a filament dryer.
The key is to use a low and controlled temperature sufficient to drive out the moisture without softening or deforming the filament. I recommend drying PETG at around 45°C to 55°C (113°F to 131°F) for 6 hours. It’s crucial to avoid overheating, as this can damage the filament.
You can avoid moisture absorption by adequately storing your 3D printer filament. Keep your PETG filament in an airtight container with desiccants to absorb moisture.
It’s essential to store your filament in a moisture-free environment to prevent 3D printing filament from absorbing too much moisture.
5. Enable Coasting
Coasting works by stopping the extrusion of filament just before the end of a print move. When coasting is enabled, the print head uses the pressure, and the molten filament is already in the nozzle to finish the segment.
Enabling coasting significantly mitigates stringing, preventing excess filament from oozing during travel moves.
When the ‘coasting’ feature is used in a 3D printer, the extruder stops adding new filament before reaching the end of the current printing path. By eliminating nozzle pressure, your 3D printer prevents unwanted filament from oozing during travel movements.
To effectively use coasting, finding the right balance in the coasting distance setting is crucial.
Coasting distance is how far before the end of a print move the extruder stops extruding. If the coasting distance is too short, it won’t reduce stringing. However, if it’s too long, coasting leads to gaps or under-extrusion at the end of the segments.
Start with the coasting distance recommended by your slicing software and gradually increase it while observing the effects on your prints.
6. Clean the Nozzle
A clean nozzle is crucial for avoiding stringing. Accumulated residue creates partial blockages, leading to uneven extrusion and unwanted strings. Dust, debris, and filament residue can collect within your nozzle. After using your printer for a long time, the accumulated residues can create surface defects such as strings.
There are several ways to clean your 3D printer nozzle:
- Cold Pull: Our favorite technique for cleaning partial nozzle clogs is cold-pulling filament. It involves inserting a filament into a heated nozzle and allowing it to cool before pulling it out, removing any residual material stuck inside.
- Wipe the nozzle head: Use a small wire brush to gently scrub the nozzle’s exterior to remove external debris and burnt-on filament.
- Cleaning filament: Cleaning filament is a special kind of filament designed to clean the inside of the print head. Simply load the cleaning filament and heat the print head to the normal printing temperature, and it works to capture and remove debris and filament residue as it extrudes.
- Using a Needle or Pin: For finer clogs, a thin needle or pin can be inserted into the nozzle tip when heated to dislodge any blockage.
- Acetone: If you’re really struggling to clean the nozzle, an acetone bath can remove tricky contaminants.
- Replace the Nozzle: Filament wears the sides of the nozzle, leading to inconsistent nozzle diameters. Some printer nozzle materials like brass wear faster than stainless or hardened steel. Consider replacing or upgrading your nozzle for better performance.
7. Use a Quality PETG Filament
If you want to achieve quality 3D prints, it’s best to stick with the best PETG filaments. Upgrading to a quality PETG filament can make a big difference in the quality of your PETG prints.
Reputable manufacturers use quality materials, equipment, and production techniques to ensure a better product with better tolerances.
You should only print with PETG filaments with a tolerance of +/-0.05mm. The tolerance means that the diameter of the filament may be 0.05mm thicker or thinner when measured at different points.
Smaller tolerances generally mean a higher quality filament. Lower-quality filaments have higher tolerances, which can produce inconsistencies in your printing.
We recommend printing with Overture PETG, which has a +/- 0.03mm tolerance.
8. Enable Combing
Combing is a feature that adjusts a travel path to limit the time the extruder spends over empty spaces. Combing reduces stringing by restricting the nozzle’s time traveling over open spaces.
The primary advantage of this approach is that it minimizes the number of times the nozzle crosses empty space, where oozing and stringing are most likely to occur. By traveling over already printed areas, any oozing is less visible as it’s deposited over existing print lines rather than in open space.
Enabling combing doesn’t eliminate stringing because it doesn’t directly affect filament extrusion. Instead, combing reduces the amount of stringing in your prints.
The downside to combing is that it can add to your overall print time as travel paths become longer. Furthermore, in some cases, especially on prints with intricate details or small spaces, combing can lead to issues like over-extrusion or surface imperfections on the top layers, as the nozzle may drag oozed filament over printed areas.
If adjusting the settings above doesn’t reduce stringing in your 3D prints, you may want to try combing.
We only recommend combing when combined with retraction, coasting, and optimized travel speeds to reduce stringing without compromising the overall print quality.
How to Remove Strings From 3D Prints
Dealing with PETG stringing in your 3D prints isn’t fun.
You can remove most of the stringing by hand. But there will always be stubborn bumps and strings.
You can remove the residual strings with a heat gun or small torch for a smooth surface finish.
Ensure you don’t keep the lighter in the same spot for long because the plastic may get soft, melt, or even burn.
Editor’s Note
Only use a heat gun, torch, or lighter in a well-ventilated outdoor space. Wear personal protective equipment, flame-resistant gloves, and a P100 respirator. Heated plastic can be toxic.
