How to Configure Retraction Settings for Printing TPU?

While it’s no secret that configuring retraction is a tricky process with a lot of trial and error required for the task in general, configuring retraction for TPU, in particular, is even more of a challenge due to the flexible nature of the filament bringing some additional limitations.

In this guide, we will take you through the process of configuring retraction settings optimally for printing TPU filament with both Bowden and Direct Drive extruders and discuss the effects of printing TPU with too much or too little retraction to make it easier for you to find out whether your retraction settings are configured correctly.

How to Configure Retraction Settings for Printing TPU with a Direct Drive Extruder?

In regards to configuring retraction for printing TPU with a Direct Drive extruder, we will be discussing the retraction speed, retraction distance, retraction extra prime amount, retraction minimum travel, and retraction minimum extrusion distance window (together with maximum retraction count) parameters of Cura individually, which we can consider to be the primary parameters that make up the retraction settings that you will need to adjust for a successful print.

Retraction Distance

Retraction distance, which determines the distance that the filament will travel away from the nozzle whenever a retraction occurs, is perhaps the most critical retraction-related parameter to correctly adjust when printing with TPU, as the flexible nature of TPU practically makes it impossible to use high retraction distance values.

cura retraction-distance


When printing TPU with a Direct Drive extruder, we recommend setting the retraction distance to a value between 0.5 mm to 1.5 mm as a starting point for your first test print, which should ensure that you don’t face severe issues related to the retraction distance being neither too high nor too low.

In a scenario where the retraction distance value you’re using is higher than optimal when printing with TPU filament, the primary issue you can come across is extruder clogging, as constantly retracting (and priming) an extended length of filament will increase the likelihood of it bending at some point due to its flexible nature, at which point the extruder won’t be able to move it anymore.

Our recommendation to resolve this problem would be to reduce the retraction distance by 0.1-0.5 mm at a time and to keep testing until you find a retraction distance value where the clogging problem does not occur anymore.

Similarly, in a case where your retraction distance value isn’t high enough, the very first problem you will notice is filament oozing, whether it’s in the form of blobs appearing on the surface or stringing, as the shorter you pull the filament back, the less time it will require to ooze back out of the nozzle again.

To reduce the oozing, you will need to go the opposite way instead and increase the retraction distance by 0.1-0.5 mm at a time across tests, and once again, keep testing until you find the optimal retraction distance value where no blobs or stringing is present on your prints.

Considering that the issues you will experience as a result of the retraction distance being too high are more severe, our recommendation would be to start from the lower end of the range we have mentioned if you have never tried printing with TPU before, and to increase it slowly to the highest value where the filament doesn’t end up clogging the extruder, as this will minimize oozing.

Additionally, if you want to take your testing & optimization a step further to find the optimal retraction distance value without the need for multiple test prints (but at the expense of spending some time setting things up initially), we highly recommend printing a retraction tower, which is a 3D model that’s split into different sections for the purposes of testing different retraction distance (and speed) values in a single print.

tpu retraction tower preview


While there are a few different ways to do this, our recommendation to get things rolling in the most convenient way possible would be to use the Calibration Shapes plugin for Cura, which includes both the 3D model and the script to make it possible to print a retraction tower directly in Cura without requiring any external files.

tpu retract tower script distance example


For more information on how to use the Calibration Shapes plugin, you can refer to the plugin’s GitHub page and the section about the retraction tower component in specific, which will take you through setting the tower up and correctly configuring it to test the retraction distance values of your choice.

Retraction Speed

Another parameter that plays a crucial role in deciding whether your 3D printer can retract TPU without issues that can stem from its flexible properties is retraction speed, which determines how quickly your 3D printer will pull the filament back whenever it triggers a retraction.

cura retraction-speed


When it comes to configuring the retraction speed, our recommendation would be to opt for a value that falls between 20 mm/s to 40 mm/s as a starting point for the test print, which we can consider to be the middle ground that’s not too slow, but not too fast either.

If you end up using a retraction speed value that’s way too high for printing TPU optimally, it’s likely that you will come across the extruder clogging problem, similar to when you use a retraction distance value that’s too high, as pulling and pushing the filament too quickly will increase the chance that it eventually compresses and creates a clog.

In such a scenario, our recommendation is to decrease the retraction speed by 5 mm/s at a time and to keep running the tests until the clogging problem doesn’t occur anymore, which will allow you to arrive at the highest retraction speed value (or at least close to it) where your prints won’t fail anymore.

On the other hand, if you end up using a retraction speed value that isn’t high enough, you will see an increase in the size of the blobs, particularly at the locations where retraction takes place, as the nozzle will stay in the same place for an extended amount of time while your 3D printer is performing the retraction slowly, which effectively means that more material will ooze out of it until the filament is fully retracted.

In this case, we recommend increasing the retraction speed by 5 mm/s at a time across tests with the aim of getting it to the highest point possible where the extruder doesn’t end up getting clogged as a result of using a too-high retraction speed value, which will allow you to both minimize blobs and reduce print times.

With that said, our recommendation when we put all the outcomes into consideration would be to start with a value that’s toward the lower end of this range to rule out the risk of extruder clogging and to work your way up to the highest value possible where extruder clogging isn’t a problem, which will be the safest way of calibrating the retraction speed.

Similar to the process of optimizing the retraction distance, printing a retraction tower will also be your best friend to quickly test different retraction speed values within a single print and pick out the one that’s performing the best results, with the only difference being the retraction distance value staying stable this time and the retraction speed value changing across the segments.

tpu retract tower script speed example


Retraction Extra Prime Amount

The retraction extra prime amount value determines the amount of extra filament your 3D printer will prime after each retraction, which makes it a situational parameter that you will only need to configure in cases where you need to compensate for material that’s lost to oozing during the travel moves that take place after retractions.

retraction extra prime amount


So, provided that you haven’t experienced any under-extrusion problems or haven’t even printed with TPU filament so far, the correct value for the retraction extra prime amount parameter will be 0 mm^3, which effectively means that your 3D printer won’t apply any compensation to the amount of filament it primes after a retraction.

On the other hand, if the occurrence of under-extrusion, specifically after retractions, is a problem that you’re observing on your prints frequently; our recommendation would be to increase this value in small increments, such as 0.05 m^3 at a time, which should get your 3D printer to make up for the filament that’s lost to oozing, and stop under-extruding after retractions.

While the actual solution to the problem you’re facing would be to entirely eliminate oozing instead of getting your 3D printer to prime more filament to compensate, this may not always be possible due to the amount of retraction you can use becoming limited when printing with TPU, which makes the usage of the retraction extra prime amount feature a quick fix that you can apply to resolve the under-extrusion problem you’re experiencing.

Retraction Minimum Travel

The retraction minimum travel value determines the minimum distance the printhead needs to move for a retraction to be triggered before the travel move occurs, and even though this isn’t a parameter that you will need to tune explicitly for TPU, it’s still one that we want to mention for optimal retraction configuration.

retraction minimum travel


While it may sound unintuitive to limit the frequency of retractions based on the distance that the printhead will travel, this limit actually prevents the nozzle from dropping an excessive number of blobs as a result of stopping and starting all the time in cases where your 3D printer needs to move short distances frequently, which can otherwise suddenly turn into a field of blobs.

Combining this with the fact that stringing doesn’t really occur over short distances due to there not being enough time for the plastic to ooze before the printhead reaches the extrusion path and starts extruding again, retracting the filament over such short distances doesn’t really bring a benefit on the front of stringing reduction anyway, which makes this limit highly beneficial for the quality of your prints when configured correctly.

For the most part, we can consider the Cura default of 1.5 mm to be a good starting point for the retraction minimum travel value when printing with practically any filament, and TPU is no exception here.

Once you have the test print at hand, if you come across a high number of blobs, especially in the areas where the printhead had to move short distances during printing, our recommendation would be to increase this value by 0.5 mm, test again, and repeat this process until you find the point where the blobs stop appearing.

On the other hand, in the scenario where you observe stringing across short distances, you will need to decrease this value by 0.5 mm instead to get your 3D printer to retract the filament across such short distances and keep testing until you arrive at a point where stringing isn’t a problem anymore.

Minimum Extrusion Distance Window & Maximum Retraction Count

The minimum extrusion distance window and maximum retraction count values determine the maximum number of retractions that can take place within a particular length of the filament.

minimum extrusion distance window cura


As an example, if you have a maximum retraction count of 20 and a minimum extrusion distance window of 4 mm, your 3D printer would only be able to retract the same 4 mm of filament 20 times and then stop until the retraction that took place 20 times ago was farther than 4 mm back.

maximum retraction count cura


While the purpose of this limit, similar to the retraction minimum travel limit, may not be too apparent at first, it actually plays the critical role of preventing filament grinding, which is an issue where the filament gear ends up wearing a particular portion of the filament down by constantly pulling and pushing it to the point where it becomes impossible for the extruder to move the filament due to the gear not being able to grip it anymore.

When configuring the minimum extrusion distance window, the rule to follow is pretty straightforward, which is to set it to a value that’s equal or at least close to the retraction distance value, as this will allow you to control the frequency of the retractions with the maximum retraction count value alone while keeping minimum extrusion distance window stable.

While it’s hard to say something about maximum retraction count without seeing results, our recommendation as a starting point would be to multiply the minimum extrusion distance window with 5, such as a value of 30 for a minimum extrusion distance value of 6 mm, which should allow enough retractions (5 per 1 mm of filament) to take place to minimize stringing while not grinding the filament too much.

If you come across the filament grinding problem, where the print would essentially fail due to the filament not moving, which would point toward a too-high maximum retraction count value, our recommendation would be to decrease the value by 5 at a time and to test again until issues don’t occur anymore, which should allow you to find the optimal value.

On the other hand, in the case where you experience stringing due to retractions stopping altogether at particular points of the print, which would signify that your maximum retraction count value is too low, you should instead increase it by 5 and keep running tests until you find the value where the stringing problem doesn’t occur anymore.

How to Configure Retraction Settings for Printing TPU with a Bowden Extruder?

If you have a 3D printer with a Bowden extruder, our recommendation would be to deactivate retraction entirely when printing with TPU filament, as the presence of the PTFE tube makes it extra likely for the flexibility of TPU to lead to the clogging of the extruder as a result of the constant retracting and priming movements, with the filament eventually bending / compressing within the tube.

cura disable retraction


Since the extruder getting clogged effectively means that your print will fail, as your 3D printer won’t be able to move the filament around anymore, finding ways that don’t involve retraction to reduce oozing is the best way to print TPU successfully with a Bowden extruder, especially considering that oozing alone, especially when it’s not too severe, won’t cause your print to fail on its own.

When it comes to the actions you can take regarding reducing stringing without retraction active, the first very first thing we recommend doing is to enable the Combing feature with the option Within Infill, as this will prompt Cura to create the travel paths in a way that prevents the nozzle from moving over the parts of the print that will be visible from the outside, even if it causes the travel path to become longer.

This way, the nozzle will avoid crossing the inner walls, the outer walls, and the skin whenever possible by making detours, effectively creating a scenario where any oozing, whether it’s stringing or blobs, takes place within the infill that won’t be visible from the outside once the printing process is over.

cura combing


Another adjustment you can make to reduce stringing without retraction when printing TPU is to enable the Coasting feature, which practically tells your 3D printer to cut off some of the extrusion (amount determined by Coasting Volume) toward the end of the extrusion path and use the oozed material to finish up the line instead.

As the extrusion is cut short and any oozed material ends up being used for the last bits of the extrusion path, there won’t be anything left to ooze once the nozzle finishes up the extrusion and prepares to move to the next location, which will naturally reduce blobs and stringing.

That being said, as incorrectly configuring this feature can lead to under-extrusion by cutting off the extrusion too early, benefitting from this feature may not be as straightforward as it is with the Combing feature, which is why we recommend running some tests to dial the value in before moving forward with your actual prints.

cura coasting


Finally, one last relatively quick fix you can apply to reduce stringing without retraction is to decrease the printing temperature toward the lower end of the temperature range that the manufacturer recommends.

As the printing temperature you’re using directly affects the flow of the material, with the usage of too-high temperatures even causing over-extrusion, taking the heat down a notch will slow down the filament flow and make it less likely for it to ooze out as the nozzle travels from one spot to the other.

Conclusion

As incorrectly configuring the retraction parameters can easily lead to a disaster scenario when printing with TPU where the filament clogs the extruder and causes the print to fail completely, ensuring that you have retraction dialed in is one of the vital steps of printing TPU and obtaining high-quality results.

With this in mind, thoroughly testing your retraction settings before moving forward with a print is something that we specifically recommend, even more so than when you configure retraction for another type of filament, as this is the only way to ensure that everything goes smoothly right from the start.