Retraction in Action! Eliminate Stringing & Improve the QUALITY of Your 3D Printed Models

No one likes to have to clean up a bunch of stringy mess on a 3D model that they just finished printing! But what is the cause of that stringy mess and what can you do to eliminate, or at least greatly reduce the amount of stringing on your models? Here we delve into RETRACTION and how it is one of the most important factors in determining the quality of your 3D print jobs.

By enabling & tweaking your RETRACTION settings in your slicing software you can instruct your 3D printer to momentarily pull back some of the un-melted filament from the melt zone while the printer nozzle is traveling over a non-print area. This will help reduce the pressure in the nozzle on the molten plastic – which leads to the oozing and leaking that directly causes stringing.

We will also cover other settings such as temperature of the melted filament and the travel speed of the printer nozzle and how those factors can also contribute to stringing. Finally, we will explain various terms associated with retraction and some additional setting parameters for you to try to eliminate any stringing you my be experiencing when printing your 3D models.

Oh, and yes, of course we had to learn a LOT of this the HARD way…..

What Causes “Stringing” When Printing a 3D Model?

Definition of Stringing with Regards to 3D Printing:

Simply said, stringing is thin wispy threads of melted plastic filament that continues to move out of the hot end of your 3D printer while the printer head is moving during non-print times from one print location to another. Even though the extruder is no longer pushing un-melted filament into the melt zone during these non-printing movements – the built up pressure in the nozzle remains high enough to cause some of the already melted filament to leak out of the printer head. It is in essence OVERFLOW seeping out where no melted filament was intended to be deposited between print areas or off to the sides of print areas of the model.

What are the causes of stringing when 3D printing? – There are three (3) main causes of stringing:

Too much pressure in the nozzle during non-printing time as the nozzle travels over a non-print area,
Printing at higher temperatures – the higher the temperature the more liquid the filament will be, and therefore more likely it will leak out of the nozzle when traveling over non-print areas, and
The speed that the print head moves from one print area, over a non-print area to the next print area. The faster the print head moves from a print area over to a non-print area, the more likely it is to result in stringing.

Poor retraction settings led to this messy print – and a LOT of work to clean it up!

Another example of poor extrusion settings. Gracie printed this Rubik’s Cube holder after she was first able to solve the Rubik’s Cube on May 10th 2020. Her name and the date are on the other sides. As you can see – there is a massive amount of stringing between the printer areas on all sides!

Retraction Defined (For 3D Printing)

Retraction: Retraction refers to the distance the un-melted filament is retracted -or pulled back – towards the extruder motor (feeder) to reduce the pressure on the melted filament inside the nozzle. If the pressure is reduced on the melted filament in the nozzle – it is less likely that there will be leaking or oozing of melted filament from the print head as it is traveling from one print area to another. Leaking and oozing over these travel areas that are NOT print areas are what lead to stinging and nodules. Increasing the retraction levels can be one of the most effective means of reducing stringing associated with 3D printing.

Note – that it is the still solid and un-melted filament that is retracted from the melt zone in the printing head to reduce the pressure in the nozzle so that no additional melted filament is extruded through the print nozzle during non-printing moves. No melted filament is actually pulled, or sucked, back into the hot end (nozzle) of the printing head!

Primary Steps to Reduce Stringing

Adjust your RETRACTION settings! That is what we are focusing on in the this post.

Make sure RETRACTION is enabled. In CURA 4.7.1 you can find this under the “Travel” tab in the settings. (If you are unable to see it there you will need to go into the “Settings” menu in the upper left hand corner, select “Configure Setting Visibility” and then “Settings”. There you will be able to check mark the settings that you want to be visible in your settings menu.)
Increase the Retraction Distance. – This is the distance, in mm, that the un-melted filament is pulled back away from the melt zone (and through the Bowden tube) towards the extruder motor. I would suggest that you try something like 5 mm for retraction distance first – and then go from there in increments of +/- 1 mm, generally staying within the range of 3 to 10 mm.
Increase the Retraction Speed – Increase the speed at which the un-melted filament in the Bowden tube is pulled away from the melt zone and back towards the extruder motor. I would recommend that you try 30 mm/s first – and then go from there in increments of +/- 5 mm/s.
Limit Support Retractions. As indicated above – too much of a good thing can be bad. So with regards to retraction – consider only using retraction when printing parts of the actual model as opposed to the supports that you may need to print the model. After all, it doesn’t really matter if there is a little stringing around the supports!
Maximum Retraction Count. By default – this is set to 100 in Cura – which is probably way too high! This is the amount of times retraction can occur over any specific area of filament. If it is too high – the un-melted filament may be damaged – which may lead to areas of the print suffering from under- extrusion problems. Better to set this to something in the 10 – 35 range.
Enable Coasting (Coast at End). You can find this under the “Experimental” settings tab in CURA 4.7.1. Even with retraction enabled – it still takes a small amount of time for the oozing of melted plastic at the hot end of the printer to stop. So that is why there is a setting for coasting. Coasting instructs the 3D printer to actually stop extruding melted filament just a fraction of a second before the end of the area to be printed. It relieves some of the pressure at the nozzle just before it travels over a non-print area and reduces the need to use retraction. That way any material that oozes out of the nozzle will be deposited in the print area rather than the travel area – thereby reducing stringing.

Other Settings to Adjust to Reduce Stringing for 3D Printing

So now that we understand what retraction is, how it relates to preventing stringing on our 3D models, and the primary settings we should adjust – what are some other settings we might need to become familiar with to further reduce stringing and improve the quality of our 3d printed models?

Tinker with your print speed. You can try both increasing print speed and reducing it.
1. If you are using a lower temperature to print at you may find that at higher print speeds (say 200 mm/s) you are experiencing under-extrusion. (Where areas of the print have too little melted plastic deposited) If that is the case – try lowering the print speed, maybe even as low as 20mm/s.
2. On the flip side, If you need to leave the temperature on the higher end, increasing the print speed may actually reduce stringing – as there is less time available for oozing and leaking from the nozzle during travel times.
See if you can lower the temperature of the nozzle for printing. Just lowering the temperature about 10 – 20 degrees (C) may be enough to prevent stringing. As I indicated earlier – the higher the temperature, the more liquid the filament will be, and therefore more likely it will leak out of the nozzle when traveling over non-print areas. When printing with PLA (like we usually do) we sometimes reduce the printing temperature to 180 °C from 200 °C which we usually use if we are having trouble with stringing.
Enable Wiping (Outer Wall Wipe Distance / Wipe at End). Wiping moves the extruder back over the print area just completed to deposit any oozing before moving on to the next print area.
Enable Combing (Avoid Crossing Outlines). Combing is a combination of wiping, coasting, and redirecting the travel path of the print head – so it is staying within the perimeter of the print for longer or eliminating it from crossing some open space to reach it’s next print location. This minimizes travel over open areas, thereby minimizes opportunities for stringing. Although it does result in more travel distance of the extruder head – it reduces the need for material retraction and can reduce the number of print defects on the outer surfaces of your 3d print model. This setting can be found under the “Travel” settings in CURA.

Image courtesy of Ultimaker. On left the purple shows the path of the print head travel over open areas. This is WITHOUT combing enabled. On the right (with **COMBING ENABLED**) – you can see that the print head has been re-directed over previously printed parts to essentially wipe any oozing material over a print area – to reduce stringing.

6. Please Note, it is possible to have too much of a good thing! Too much retraction (both speed & distance) can result in pock marks due to under-extrusion in those areas which is too little melted filament being deposited in the print area. It can also result in the un-melted filament getting a little chewed up from the additional travel through the extruder gears – which could eventually cause it to slip and manifest itself with under-extrusion in areas of your print. If you are starting to see dust around the extruder assembly – that might be a good indication that your retraction settings are causing some grinding of the un-melted filament.

7. Z-Hop: With Z-Hop enabled the print head moves up relative to the print model when retraction is performed – allowing the nozzle to travel over the printed parts of the 3D model without touching them.

8. Minimum Extrusion Distance Window. This determines the length of filament that the Maximum Retraction Count is implemented on. Any retraction commands in excess of the Maximum Retraction Count will be ignored for the given Minimum Extrusion Distance Window. So if the Maximum Retraction Count is set to 10 over a 5mm segment, any Retraction commands in excess of 10 will be ignored over any given 5mm segment.

9. Retraction Minimum Travel. This helps eliminate all retraction for very small areas of travel. If travel is not equal or greater than the length set here, then retraction will be prevented from occurring at all. Leave at the default of 1.5 mm.

10. Nozzle Switch Retraction Distance, Nozzle Switch Retraction Speed, Nozzle Switch Retract Speed, Nozzle Switch Prime Speed and Nozzle Switch Extra Prime Amount are all only relevant for 3D Printers with more than one printing nozzle. Since this does not apply to single nozzle printers – just leave it at the default settings. My understanding is that CURA does not like you reducing any of these settings to 0.

Definition: Priming. After the printer performs a retraction – the push back into the Bowden tube towards the melt zone is what is called “priming”.

Summary of Recommended Settings & Action Plan to Reduce/Eliminate Stringing for Your 3D Printed Model

Here are the settings I have been having success with lately. Remember – it is BEST to make as few changes to the settings to achieve the desired result of a clean print with minimal or no stringing!

Our printer & retraction settings in CURA 4.7.1 for our Creality Ender 3 Pro.

First Line of Defense Against Stringing

Enable Retraction in your slicing software
Set you Retraction Distance to 5 mm first – and then go from there in increments of +/- 1 mm, generally staying within the range of 3 to 7 mm.
Set Your Retraction Speed to 30 mm/s first – and then go from there in increments of +/- 5 mm/s staying with the range of 10 to 70 mm/s.
Enable Limit Support Retractions.
Change Maximum Retraction Count to something between 10 -35
Enable Coasting.
Leave all other retraction settings at default values.

Second Line of Defense Against Stringing

Consider reducing the speed of the print. Start @ 50 mm/s.
Consider lowering the temperature of your print. For PLA although 200°C might be where you try first – don’t be afraid to consider using something as low as 180°C.

Third Line of Defense Against Stringing

Enable Combing Within Infill
Enable Z-Hop

Basic Retraction Test Model

Here is a link on Thingiverse to the model I used to calibrate our 3D Printer. Thank you Southwester Applied Physics. Basic Retraction Test

Conclusion

Your retraction settings will most likely be one of the biggest factors determining the quality of your 3D printing jobs. Here we explained and reviewed many of the settings that you will need to be familiar with to properly adjust your retraction settings and eliminate stringing when printing your 3D models.

Although you may find the setting parameters that I provide here to be helpful as a baseline for your settings – you will likely have to refine them further for your specific printer and situation. Dealing with stringing, retraction settings, and 3D printing in general, can be frustrating at times! Just remember you will have a LOT less frustration if you are methodical in your approach and document the variables you change when trouble shooting. As an added benefit, it will also be much easier to replicate your successes in the future!

Keep things simple and don’t fix something that is not broken. The goal is to get the best print possible with the minimum amount of adjustments – including retraction.

Sincerely,