3D Print Troubleshooting - Stringing

Stringing can be a very frustrating print problem to troubleshoot. It can depend a lot on the geometry of your print; some models may have problems with stringing while others may not even if you slice using the same settings. In this article, we'll go over the causes of strining, and what you can do about it.

What Causes Stringing?

Before we can trpubleshoot stringing, it's critical to understand the underlying cause of this issue. The basic cause of strining is molten filament continuing to ooze out of the nozzle during a travel move. The filament gets pulled into a thin "string" by the movement of the nozzle, leading to the unwanted artifacts on the final print. This oozing can be caused by several factors, including:

• A build up of pressure in the nozzle before the travel: Excess pressure can cause filament to ooze out during travel.

• A very high printing temperature: Keeping the filament at too high of a temperature can make the filament too liquid during travel, leading to ooze.

• Water absorbtion into the filament: Waterlogged filament can bubble on contact with the nozzle, leading to stringing.

• Poor nozzle condition: Worn or clogged nozzles can lead to inconsistent extrusion.

How can you mitigate stringing?

Retracting before travel

By far, the single most important setting to handle stringing is filament retraction before travel. Retracting the filament relieves the pressure of the filament into the nozzle and prevents ooze. If you're experiencing problems with stringing, try increasing the distance the printer is retracting the filament or the speed at which the retraction happens. For bowden tube printers the retraction distance is typically higher than for direct drive printers: 3-10mm for bowden tubes and 0.5-2mm for direct drive extruders.

Increase the retraction distance a quarter millimeter at a time and see how the stringing performance is changed. Increase the retraction speed by increments of 10% of your printer's original retraction speed and check is stringing is reduced.

While you are tuning your retraction distance, be careful not to set it too high. For a direct drive extruder, retraction distances that are too high could eject the filament out of the extruder entirely!

It's important to also be aware of your minimum retraction travel distance, which sets the threshold distance above which the extruder retracts. For shorter travel moves, the extruder does not retract in order to save time. If this is set too high, the extruder may not be retracting as often as it should be.

If you're having trouble with stringing over short distances, set this minimum retraction distance to zero. Then, gradually increase it by increments of 1mm, testing performance at each increment.

Your retraction settings will not be the same across different types of filaments, or even different brands or colors of the same type of filament. Just because a set of retraction settings worked well for one kind of filament doesn't necessarily mean they will work well for even another very similar type of filament.

Print Temperature

Ooze can also form during travel moves if the print temperature is too high. By lowering the nozzle temperature, the filament remains slightly more solid and less prone to ooze.

Set your extruder temperature to be in the middle of the recommended range listed by the manufacturer (typically listed on the filament spool). Then, lower your nozzle temperature 5 degrees at a time; if your extruder gear starts skipping, the print temperature is too low.

One problem with this lower temperature approach is bed adhesion: A lower print temp may affect the part's ability to stay affixed to the bed. For this, most slicers support a "First Layer Print Temperature" where you can set your print temperature to a higher value at first, then lower it for the rest of the print.

Keep your initial layer temperature the same, and only modify the temperature for higher layers.

Additionally, increasing the part cooling fan percent can help cool any ooze quickly and prevent stringing. For filaments like PLA, set the fan speed to 100%. For filaments like ABS, be more cautious; increase the fan speeds in increments of 10% and observe the effect on strining. Too high of a fan speed can cause poor layer adhesion in ABS.

Water Absorption

It might seem counterintuitive, but your plastic filament can actually absorb water from the air. When this waterlogged filament comes into contact with the nozzle, the water evaporates and it can cause incosistent, goopy extrusion. Using a dedicated filament dryer is ideal, but filament can also be dehydrated by placing it in a box with dessicant packets or placing it in an oven at a very low temperature. Different filaments absorb water to different degrees, with nylon being one of the most absorptive.

Set your oven to a relatively low temperature like 50 decrees Celcius (120F) and place your filament spool in the oven for around an hour. In a pinch, you can also dry your filament if you have an enclosed printer: simply set the build plate temperature to 60-70 degrees celcius and place the filament spool on the build plate. The goal is to heat up the filament enough to dry it out, but not to get it anywhere near it's glass transition temperature.

Nozzle Condition

A partially blocked or worn nozzle can also lead to excessive stringing. Clearing a blockage may be performed by a "cold pull", which involves heating up the nozzle, letting it cool down, and manually pulling the filament out once the filament solidifies.

Swapping to a new nozzle prevents a lot of problems. To swap a nozzle, first heat up the printer and eject the filament. Then, unscrew the old nozzle while the printer is still hot. Finally, screw in the new nozzle. Inserting the new nozzle while the printer is hot is critical, this ensures a strong seal of the nozzle against the heat block.

Preventing Stringing on Part Exteriors

If you can't prevent stringing entirely, there are other great ways to prevent stringing from showing up on the exterior of the part.

Travel Speed

Increasing travel speed can help make stringing less severe. The increased speed helps break the strings early in the move, preventing longer, continuous strings from forming. Remember that in addition to increasing travel speed, you also need to increase the travel acceleration to be able to achieve that speed.

Start by setting the travel speed and acceleration to your printer's recommended default settings. Then, increase these settings in increments of 5% of the default values and observe the effect they have on stringing.

Combing and Coasting Modes

Some slicers have a mode called "Combing" that ensures the nozzle stays inside the model during travel moves. While this does not prevent stringing, it does make sure that the strings occur inside the model. While in Cura this is called "Combing Mode", in the Bambu Slicer this is called "Avoid Crossing Wall".

Coasting can also help. Coasting lessens the flow of filament right before travel moves, which decreases the pressure of the filament in the nozzle and prevents stringing.

Enable different combinations of combing and coasting and observe how they affect stringing. Coasting can lead to underextrusion before travel moves; if you are seeing underextrusion, decrease the coast distance in increments of 1mm until this is resolved.

Seam Alignment

The places where the nozzle starts and stops printing on the edge of the model form what most slicers call a "Seam". Most slicers default to placing the seam either in one place along the entire model or placing the seam in the place that ensures fastest printing.

Set your seam placement to "Random". This will ensure that strings cannot build up over time.

Obico

One of the best ways to diagnose stringing problems is to watch your print remotely. Obico lets you set up monitoring for your printer and integrate it into your slicer.

To set up Orca Slicer with Obico, follow the instructions in this guide: Obico Integration Guide