3D Prints Stringing?

So you returned to your printer, excited to see your finished print, only to find wispy strands of filament stuck to your print.

Stringing is a relatively common defect in 3D printing. While it’s often minor, it can be tedious to remove and can ruin the appearance of your print, sometimes forcing you to start over.

In this blog we’ll discuss what stringing is, why it happens, and how you can prevent it. Plus, we’ll go over how QuinlyVision, our multi-failure detection system that is able to detect and respond to 14 different 3D print failures and defects, is able to identify stringing.

What Does Stringing Look Like & Why Does It Happen?

Chances are you know what stringing looks like and are here to figure out how to fix it, but in case you’re just reading this for fun: strings are wispy strands of filament scattered across the build plate. They are no thicker than a couple of strands of hair, and they can be very difficult to remove from your print because they’re so thin.

Okay, now that we’re all on the same page about what stringing is, why does it happen? Stringing occurs when material oozes out of the nozzle while it travels from one place to another. It can come as a result of poor settings or from other failures that are occurring, such as over extrusion and under extrusion.

Some reasons you may be experiencing it are that you have the wrong retraction settings, incorrect nozzle or bed temperatures, or material that is retaining moisture. Each of these causes has a relatively simple fix which we will go over in the next section, along with some additional helpful settings to try.

How To Prevent Stringing

1. ‍Check that retraction is enabled in your slicer. Retraction lifts the material out of the nozzle slightly so that liquid filament is held in the hotend far enough from the tip that nothing leaks out during travel moves. There are two critical settings when it comes to retraction.
   
   Retraction Distance refers to how much the material gets retracted out of the nozzle into the hotend, and is dependent on what system you have. We recommend the following:
             Bowden: >3mm
             Direct Drive: 0.5mm-1mm
   
   ‍Retraction Speed on the other hand is how fast the material gets retracted. Ideal retraction speed is a bit harder to figure out, so you will likely have to experiment a bit with different speeds to see which works best for you.
   A general rule of thumb to follow is:
             Larger nozzle: use a slower retraction speed
             Smaller nozzle:  use a faster retraction speed
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2. Make sure you’re printing at a reasonable temperature. Stringing can happen if you print too hot, but if you use a slower print speed, you can usually get away with using a lower temperature. If you think incorrect temperature might be causing your stringing, our suggestion is to drop your temperatures by about 10°C and slow your print down slightly.
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3. Dry your filament. If you notice a crackling or popping sound during your print, it means your filament has moisture inside that’s essentially getting boiled in the nozzle. This can happen with PLA, but it’s much more common with materials that absorb a lot of water such as nylon. You can purchase a filament dryer or just use your oven (WARNING POTENTIAL FIRE HAZARD: If you are going to DIY filament drying be sure to look up a tutorial to avoid starting ruining your filament, your oven, or worse!).
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4. Try additional settings. Some slicers have extra settings that can help prevent stringing during travel moves, so if you haven’t looked much into preventative settings, here’s where you can start.
   
   Combing forces the nozzle to avoid crossing open gaps and redirects travel moves to take a different path so it only travels through infill. This way if there is any stringing, it is hidden within the part. Combing is usually only good for short distances. If your nozzle has to travel a long distance, then it is still a good idea to use retractions instead. Cura has a setting for this called Max Comb Distance With No Retract. Setting this to 10 mm is a good starting point but you can go as high as 50 mm.
   
   ‍Nozzle wipe adds a small travel move right before a retraction, which can clean the tip of the nozzle slightly so that the retraction happens cleaner.
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5. Settings to avoid:
   
   ‍Z Hop can actually cause stringing if it is enabled. This setting lifts the nozzle in the Z direction before it moves horizontally, sometimes pulling plastic along with it, causing stringing. Unless you really need Z hop for other reasons, this is best left disabled.
   
   Coasting should also be avoided. It replaces the last section of an extrusion path with a travel move, so that some ooze will be used as part of the print. This setting is hard to calibrate and is often used as a bandaid fix.
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6. Inspect your hardware. Tighten screws on the extruder, bowden tube, and hotend, and check that nothing is loose or rattling. Make sure that the bowden tube is pushed into your hotend as far as it can go and that the retaining clip on the bowden coupler (these are usually blue plastic) is keeping it firmly in place.
   

How Does QuinlyVision Identify Stringing?

As we mentioned earlier, stringing may be a minor defect in some cases, but in others it can ruin your print and there’s currently no system that detects it. QuinlyVision, however, can! So, how does it do this?

QuinlyVision goes through a similar process to you when identifying what happened to a failed print. First, it notices there is material where there shouldn’t be, then it assesses the appearance of that material. In the case of stringing, it can tell it’s not another failure (such as spaghetti) by the thickness of the strands, which are only about 1-2px wide.

Okay, this machine vision stuff is cool and all, but how does this help you? Well, there are two ways: QuinlyVision can determine the root cause of your stringing, making it easier for you to fix the problem, and in some cases it can prevent stringing entirely.

Let’s look at two scenarios:

Scenario 1: Your stringing occurs alongside under extrusion. This is because under extrusion happens when there’s not enough material in the print itself, which can be a result of material extruding where it shouldn't (e.g., during travel moves) rather than onto the print itself. You aren’t sure where to start when it comes to fixing this issue but QuinlyVision’s built-in Correction Wizard™ provides suggestions for how to fix your under extrusion (the underlying cause) rather than just fixing the stringing (what you notice first).‍

Scenario 2: Your stringing happens as a result of over extrusion because the excess material oozes out of the nozzle while it travels. If you have instructed QuinlyVision to pause your print when it identifies over extrusion, the minute that failure is detected, your print is paused, and no more stringing occurs. You can easily clean up a few wisps of filament and resume the print once you have fixed the problem, avoiding an outright failure.

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Hopefully you found this blog helpful and have some new settings to try to fix your stringing! If you're interested in QuinlyVision, try our interactive demo during our livestream this Wednesday, June 22 from 4:30-6:30pm PST.