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Stringing and oozing

Last updated 4 months ago
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Stringing or oozing, also known as "hairy prints", is the name given for when small strings of filament are left on a printed model. This usually happens when the filament keeps flowing from the nozzle while the extruder is moving to another object. You can see this as a marginal line of filament left between the objects.

This issue is caused by very high printing temperatures and/or using incorrect retraction settings. This can be solved by changing a couple of settings in PrusaSlicer and checking your hardware.

Stringing from material left on the nozzle

If you print for a long time from a single type of filament, such as PET-G, the filament can create a thin layer in the nozzle. This can cause stringing as the strands of the filament stick to the surface of the print. Therefore, thoroughly clean the nozzle before printing and make sure that any dirt or remnants of previous filaments are removed from the nozzle.

We highly recommend using our official (factory default) preset settings in PrusaSlicer. However, if you are printing with your own settings, make sure that you have the retraction settings configured correctly. 

Retraction-settings

You should start by checking a parameter known as Retraction. What does retraction do? When the extruder has finished printing one section/object of your g-code, the filament is pulled back into the nozzle. Once the extruder moves to the next location the printing process continues – the filament is pushed back out and it starts extruding from the nozzle again.

stringing

Flexible filaments usually need longer retractions, because the material stretches while being pulled back to the nozzle. Flexible materials are a special case and can need a lot of tweaking and tuning.

stringing second image

Preventing strings from happening

Use the correct value for retraction. Users often increase retraction to meaningless values, so check the PrusaSlicer settings and make sure retraction not set too high. On the MK2.5/S and MK3/S/+, retraction length should be maximum 2 mm. Retraction settings can be found in PrusaSlicer in Printer Settings -> Extruder 1.

Due to the Bowden extruder, the retraction length of the Original Prusa MINI presets are much longer (default 3.2 mm).

Make sure you have "Wipe while retracting enabled"

Try to lower the nozzle temperature – Lowering the temperature decreases the occurrence of strings. Try decreasing the nozzle temperature by 5 – 10°C and check whether there’s less stringing.

Enough settings, pass me my heat-gun!

If you don’t feel like tweaking any of the settings, well, then there is an alternative. You can get rid of the strings with a heat gun (or often with a lighter – but be very careful). Set your heat-gun to around 200°C and aim at the strings for one or two seconds. This will melt the strings, and the printed object should remain undamaged.

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