3D printing pulls strings - a scenario that everyone who deals with 3D printing is confronted with. Luckily, there are a few ways to avoid or at least greatly reduce stringing. In this post, I explain how you can get the problem under control step by step.
What is stringing and how does it occur?
In short, stringing (also called oozing) is the “pulling” of the filament . This can happen with PLA, PETG ABS or any other material. The threads are created at the moment when the nozzle (= extruder or nozzle) lifts off the material to be printed in order to move to another position.
You can imagine it like this: The nozzle, which contains liquid filament, is pulled upwards. The moment it moves to a different location, a piece of the already liquefied material gets stuck in the air and solidifies. That's exactly what the stringing threads sticking out from the print object are. They look like cobwebs and spoil the printed object, which we actually want to have nice and smooth. So what to do?
How to avoid stringing?
Unfortunately, the truth is: Stringing or oozing can hardly be avoided 100% in the long term. But you can make sure to limit it as much as possible.
The most common reasons for unsightly stringing are filament that is too hot and an incorrectly set retraction. Your job is to find out what exactly is causing the problem and then fix it. I recommend going through the following solutions step by step:
If a retraction is activated on the 3D printer, the filament is pulled back a little the moment the nozzle lifts off. The idea: the moment the nozzle starts up, there should be no more liquefied material in it that could escape uncontrollably.
The retraction is activated and set in the slicer (= program in which various settings for the printer can be made, e.g. Simplify3D or Cura). In some programs it is already activated by default. If you're having trouble with stringing, you should check and, if you haven't already, activate the retraction.
Increase retreat distance
The retraction distance describes how much the filament should be retracted. You set it in millimeters. In general, the greater the retreat distance, the less likely it is that the pressure will pull strings. Caution: If the retraction path is too large, there is a risk that the filament will not be ready quickly enough when the nozzle lowers again and the print is to be continued. So do some test prints until you find the perfect mean.
Increase retreat speed
The higher the retraction speed, the faster the filament will be retracted. So, to avoid stringing, you can try adjusting the retraction speed upwards. This is also set in the slider, using millimeters per second. Again, you'll probably need to do a bit of testing to find the ideal values.
Tip for testing proper retraction settings: Retraction Test on Thingiverse.com .
Decrease print temperature
The hotter the filament, the more fluid it becomes and the faster it can flow - so the print is more likely to pull strings. As a rule, filament manufacturers provide information on the optimal printing temperature for the material, e.g. 180-200ºC. It is best to always start with the lower temperature limit and increase it in 5-degree increments if necessary (slicer settings). If you are already printing at a higher temperature, correct down by 5 degrees incrementally until the filament pulls fewer threads. Attention: If the temperature is too low, you will have the problem that there is not enough liquid filament available for printing ("under-extrusion").
Tip for testing correct print temperature : Temperature Calibration Tower on Thingiverse.com .
Increase print speed
Another reason for stringing can be a nozzle moving too slowly across the print bed. Then the liquid filament has more time to come out of the nozzle and pull threads. The print speed is also set in the slicer. Correct them up step by step until the filament stops pulling threads. Caution: Too high speed at low temperature can cause under-extrusion.
After printing the same material for a long time, material deposits can form on the nozzle. The extruded filament then likes to stick to these deposits and pull strings. To avoid stringing and other printing problems, you should ideally clean the nozzle after each printing process (there are special needles for this, but paper and brushes can also be used). Attention: Depending on the material of the nozzle, you have to be careful when cleaning it so as not to damage it. The standard brass nozzles in particular are quite vulnerable. Accidentally nicking the opening of the nozzle can lead to stringing!
Use high quality filament
High-quality filament like that from Vision 3D is less prone to 3D printing problems such as stringing and warping - partly because it is very durable and has little variation in diameter, which helps to avoid stringing. Having said that, every time you change filament you have to start over, run tests and update the settings. If you are currently using filament of inferior quality, the switch should certainly be worthwhile.
Store filament dry
Filament that is not stored properly will lose quality over time and is more likely to pull more threads. This is especially true for PLA filament. Therefore, keep your filaments at a moderate room temperature (18 to 25 °C) and low humidity. A damp basement is therefore not a suitable place - it is better to keep filament rolls airtight (e.g. in special slipbags) in a heated room.
SOS tip if the pressure does pull threads
A few threads here and there can hardly be avoided in the long term. In this case, you can remove them with a pair of pliers and ultimately get a nice, smooth print result.
George from Vision 3D
Through intensively dealing with 3D printing, Jörg has blossomed from a complete beginner to a 3D printing specialist within a few months and has turned his hobby into a career. He shares his experiences on the Vision 3D blog.