Polylactic acid (PLA) is one of the most popular 3D printing materials. It is a common choice for beginners who want a filament that is easy to work with. Printing defects can sometimes happen, though.
PLA stringing is typically the result of an incorrectly calibrated printer. Adjusting the settings in your slicing software should solve the issue. Printing with poor quality or wet filament could also cause stringing and blobbing at the nozzle. A fluctuating room temperature is another possible cause.
6 Common Causes Of PLA Stringing
PLA stringing often happens for the same reasons PETG stringing occurs.
An incorrect nozzle temperature or retraction are the most common culprits, closely followed by poor filament quality.
1. Wrong Hot End Temperature
One of the main reasons PLA filament oozes and strings is a too hot nozzle. When the extrusion temperature is too high, the material becomes too liquid and tends to flow out of the nozzle during non-extrusion movements.
With the distance between the nozzle and build plate or the already printed part being about the same as the layer height, it is easy for the blobbing material to adhere to the layers below.
As the arm continues moving without extruding, the filament stretches and forms thin hairs.
For the first layers, stringing could also occur due to a too high build plate temperature. However, this is rare.
2. Wrong Retraction Settings
The second most common reason for PLA stringing is too little retraction. When the retraction distance is too short, the material can ooze and stick to the already-printed surface.
A too slow retraction speed can lead to the same result. Thus, it is important to consider both parameters when setting retraction in your slicing software.
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3. Too Long Minimum Travel Distance
The minimum travel distance is a function found in certain slicers, such as Cura. It determines how far the hot end should travel before enabling retraction.
While a few millimeters of travel distance can prevent problems like warping or curling at the corners, a too long minimum travel distance can lead to the same issues generated by wrong retraction settings.
Ideally, this value shouldn’t be higher than 1mm to 2mm. If you must set a longer minimum travel distance, the filament might be of poor quality or wet.
4. Clogged Nozzle
Surprisingly, a clogged nozzle can also cause PLA stringing problems.
When extrusion is blocked, some filament may remain trapped inside the nozzle. As the hot end heats the filament and the extruder pushes new material through the nozzle, the filament may form blobs that can start oozing during non-retraction movements.
A clog can also interfere with retraction, preventing the proper pull of the filament back into the hot end during non-extrusion movements. Most of these issues are known as inconsistent extrusion.
The material passes from a brittle solid into a viscous liquid (a state between solid and liquid, actually) at a lower temperature, a factor that increases the probability of oozing and stringing.
For this same reason, printing with wet filament can trigger a wide range of defects in the print. While PLA is not as hygroscopic as PETG, you should still dry it before use.
6. Poor Quality Filament
Lastly, stringing can happen due to poor quality filament (or deteriorated filament, if the spool was of good quality originally).
Poor quality filament can retain more moisture than quality one. It may also contain plasticizers that lower the glass transition point.
14 Strategies To Prevent PLA From Stringing
Now that you know what can cause PLA stringing, it’s time to find out how to solve the issue.
Follow the steps below and run a PLA stringing test after each adjustment until your print comes out perfect.
1. Keep Nozzle Clean
A dirty nozzle can cause stringing and a variety of other print defects. To keep it clean, wipe it with a damp cloth after each use and scrub off any excess material with a wire brush.
If poor-quality filament accumulated inside the nozzle, use a needle or chemical remover to dislodge it. You could also clean the nozzle in an ultrasonic jewelry cleaner.
Something to keep in mind if the material clogging your nozzle is PLA is that acetone might not remove it (this solvent works for other materials).
The reason you might want to avoid acetone is that the solvent can degrade PLA, but it makes it rubbery and sticky rather than removing it. Hence, using acetone can actually make matters worse.
If you can’t clean the nozzle properly, replace it with a new one.
2. Adjust Retraction Settings
Once you make sure the nozzle is clean, start tweaking retraction. This isn’t an exact science, since each printer is different, and each PLA spool might be different from the others.
As a rule of thumb, the right PLA retraction settings are about 7mm to 9mm retraction distance at a retraction speed between 40mm/s to 50mm/s, for printers with a Bowden extruder.
If your printer has a direct drive extruder, you may use the same speed interval but reduce the retraction distance to about 0.5mm to 1mm.
3. Adjust Hot End Temperature
PLA has a relatively low glass transition temperature and melting point of around 170°C to 180°C. The ideal extrusion temperature is a bit higher than that, from 190°C to 220°C.
A hotter nozzle can cause stringing and blobbing. A colder one can lead to under-extrusion problems.
Since you’re trying to fix stringing and blobbing issues, you should lower the temp by 5°C at a time until the problem stops.
However, don’t go below the lower threshold. If you’ve lowered the temp all the way to 190°C and stringing still occurs, the problem could be elsewhere.
4. Keep Filament Dry
As explained, wet filament is one of the reasons for stringing – in all filaments, PLA included.
Keeping filament dry isn’t difficult. You can store the spool in a specific filament box or in a sealed bag together with a few packets of silica gel.
You should also dry the filament before use in a filament dryer, kitchen oven, or food dehydrator.
5. Increase Travel Speed
The travel speed in 3D printing indicates how fast the arm is moving when not extruding.
A too low speed – especially when associated with other issues like incorrect temperature or retraction – can increase stringing chances.
Like all other adjustments, you’ll have to try and see what travel speed works best for your filament and equipment. Generally, though, you should keep this value between 50mm/s to 60mm/s to ensure good print quality.
6. Enable Coasting
Coasting is a function found in popular slicing software like Cura. When enabled, it tells the extruder to stop the motor a few seconds before extrusion is stopped.
In this way, the printer won’t end up with excess filament in the nozzle. When retraction is enabled, the material will be pulled back sufficiently to prevent stringing and oozing.
Because coasting can lead to under-extrusion, it is best to enable this function first and adjust retraction speed and distance after. Alternatively, save this method for instances when stringing is truly severe.
7. Enable Wiping
Wiping is another special Cura setting that, when enabled, wipes the nozzle onto the last extruded layer when extrusion is stopped.
This spreads excess material in a uniform layer on top of the existing print, eliminating both oozing and stringing.
The downside of wiping is that it could smear the outside of your print, resulting in visual defects. These smears could also compromise the functional role of your part.
8. Calibrate Print Speed
Sometimes, the reason for stringing is too fast or too slow printing. PLA’s ideal print speed is around 60mm/s.
You can adjust by 1mm/s at a time in either direction until the printing speed is just right.
9. Enable Combing
Together with coasting and wiping, combing is a special Cura setting.
When enabled, it alters the arm’s route during non-extrusion movements, limiting the movements over large empty spaces. These jumps are a common reason for stringing, so avoiding them is preferable.
However, keep in mind that combing can increase the overall print time.
10. Adjust Z Hop Height
The Z hop is a function that increases the distance between the nozzle and the bed or printed part when extrusion is stopped.
Its role is to prevent material oozing from the hot end from touching the print until retraction is enabled.
In most slicers, the Z hop default is the same as the layer thickness. You can double this distance from the slicer’s settings or directly from the G-code.
11. Calibrate Fan Speed
If you’re used to printing with other filaments, including PETG, you may be accustomed to leaving the fan off or using a low cooling setting.
However, PLA actually benefits from 100% cooling. If you’re concerned about layer adhesion, you could slow down the fan speed, but shouldn’t go below 50%.
To figure out which speed is right for you, lower it slowly until you find the sweet spot for your filament brand.
12. Use Quality Filament
We can’t stress it enough: buying high-quality filament is crucial, even if you’re a beginner. Poor quality filament can trigger a variety of issues, resulting in spoilt prints.
This means wasted time and resources, as well as high levels of frustration if you’re still learning to use the specific material.
The market is full of cheap options, but keep in mind that SUNLU PLA stringing is more common than Hatchbox PLA stringing.
Filaments of higher quality than Hatchbox also exist and, if possible, you should buy filament manufactured by your printer’s brand. For instance, Prusament PLA is ideal for Prusa printers.
13. Adjust Room Temperature
Beyond everything above, you should also consider the room temperature and the way it affects filament.
If the temperature is too high, it could contribute to blobbing and oozing from the nozzle, increasing stringing. That’s why you should keep the printer in a room with a temperature between 77°C and 86°C.
14. Remove PLA Stringing with a Heat Gun
If stringing occurred before you managed to adjust the settings or find the cause, you might have a chance to save the part by removing stringing with a heat gun.
The principle is very simple: you should direct the heat onto the hair strings to melt and remove them.
Before starting, keep in mind that you must be very careful. Heat guns generate high heat that could damage your entire print. The risk of burning yourself is also real.
Once the filament strings are melted, remove them with sandpaper. You can then use a smoothing method to increase the part’s visual appeal.
If you’re not sure about using a heat gun safely, or if the part is too small, you can use a hair dryer instead.
PLA Stringing And Blobbing In Ender 3 & Prusa
PLA stringing and blobbing could happen in some printers more than others. The Ender 3 and Prusa are two of the most common printers that generate these issues.
On the Ender 3, the Bowden tube’s rigidity is often the culprit. You could try printing and using a tube clip to help it get loose during retraction.
On Prusa, the most common reason is a too slow retraction speed.
As mentioned above, the retraction speed typical for PLA is around 40mm/s to 50mm/s. However, Prusa might require a much faster retraction speed, that can go as high as 80mm/s.
Another issue could be the Z lift (or hop). Increasing it by 0.2mm at a time until you get it just right might help solve the issue.
FAQs
What is a good retraction distance for PLA?
A good retraction distance for PLA is about 7mm to 9mm for Bowden extruders and 0.5mm to 1mm for direct drive extruders.
How do I know if my PLA has too much moisture?
The most common sign of too much moisture in filament is a cracking or popping sound during extrusion. The sound is the result of water vapor escaping the filament as it’s melted.
Uneven extrusion lines, uncharacteristic stringing, blobbing, oozing, poor layer adhesion, and part strength issues are other signs.
Final Thoughts
PLA is a popular 3D printing material that gives minimal trouble. However, stringing can occur when the printing parameters are incorrect. The quality of the filament and its moisture content could also result in stringing.
To solve the issue, calibrate the printer correctly, dry the filament before using it, and perform printer maintenance after each use.
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