Perfecting the 3D printing process with a new type of filament that you haven’t used before is always a challenging journey, as the unique characteristics of each type of filament cause them to behave entirely differently from one another, usually in very unexpected ways.
As a result, problems, whether they only end up lowering the quality of your print, or cause the print to fail completely, are bound to happen until you supply the correct conditions for the 3D printer to be able to succeed with the new filament, which is practically a part of the process, and not something that should be discouraging.
In today’s article, our topic will be the issue of TPU filament not extruding, and as a result, jamming the extruder, which is a reasonably common problem you can face when switching to TPU filament for the first time due to TPU being quite different compared to the common filaments such as PLA and PETG, causing it to require a different set of conditions to print successfully.
So, what can cause TPU filament not to extrude correctly and jam the extruder?
The two primary factors that can cause TPU not to extrude correctly and jam the extruder are the usage of too much retraction and a too high print speed, with both cases potentially leading up to the filament bunching up and getting stuck inside the system as a result.
In the following sections, we will be discussing each of the factors that can cause TPU filament not to extrude and jam the extruder, go through the potential solutions that will be helpful to prevent this problem from reoccurring, and finally, discuss how to make the process of printing TPU a more manageable one when using a Bowden extruder.
What Causes TPU Filament to Not Extrude & Jam the Extruder?
Since a jammed extruder will not only cause your current print to fail but also render your 3D printer unable to print until you fix it, it’s a reasonably critical problem that you will need to get to the bottom of as quickly as possible.
The primary and the most common factor that can easily cause TPU filament not to extrude correctly and jam the extruder is the usage of a print speed value that is too high, as TPU requires print speed values that are on the much smaller side compared to other popular filaments such as PLA and PETG.
When TPU filament, which is a highly flexible material, moves very quickly, it can end up compressing at any point of its journey between the extruder and the hotend, which will cause it to get stuck and prevent it from moving forward.
The second factor that can lead to a jam when printing TPU is the usage of a retraction speed value that is too high, with TPU filament also requiring retraction speed values that are much lower compared to other filaments that aren’t as flexible.
The reasoning behind the requirement for the usage of a low retraction speed is not too different from the one behind the necessity of a low print speed, with filament compression once again being a problem when it moves at high speeds.
The third and final factor that will prevent TPU from printing correctly is the usage of a retraction distance value that is too high, which is the point where things get slightly tricky, as reducing the retraction distance to a value that is way too low introduces the issue of stringing and oozing.
As increasing the retraction distance value means that the filament will be traveling a more significant distance whenever a retraction takes place, the chance of it bunching up within the system and creating a jam increases considerably.
How to Prevent the Issue of TPU Filament Not Extruding & Jamming the Extruder?
Preventing the issue of TPU filament not extruding is primarily about ensuring that all the conditions for a successful TPU print are satisfied, which will involve some trial and error until you find the optimal values.
To prevent TPU from jamming the extruder, the first step to take is to reduce the print speed value by a considerable margin, with a value that falls in the range of 20 to 30 mm/s providing a good starting point that should directly eliminate the issue.
When fine-tuning the print speed, we recommend moving up or down in steps of 1 mm/s at a time and utilizing the highest value possible where jamming issues do not occur to optimize for print time.
Next up, you will also need to reduce the retraction speed value by a decent amount, similar to the print speed, with a value that falls in the range of 10 to 20 mm/s providing the necessary optimization to ensure that the filament does not jam due to the retraction speed being too high.
For the process of fine-tuning the retraction speed, our recommendation would be to move up or down in steps of 1 mm/s at a time and stay at the lowest value possible where stringing does not occur.
Finally, the retraction distance is the last value you will be reducing, where we can consider a value of 6 mm for Bowden extruders and a value of 2 mm for direct drive extruders to be a good starting point that you can utilize to fine-tune further based on your results down the road.
For fine-tuning, our recommendation would be to move the value up or down in steps of 0.1 to 0.2 mm between each test, which will allow you to see the effects of each modification clearly. The purpose is to find a value where neither stringing nor jamming occurs.
Out of the three, the retraction distance parameter will require the most trial and error to get right due to a balanced value being required for retractions to be still capable of preventing stringing from occurring, unlike the other two, where a simple reduction of the values essentially solves the issue at hand.
How to Make It Easier to Print TPU with a Bowden Extruder?
It’s no secret that TPU filament does not exactly play well with Bowden extruders, as the flexible nature of TPU gives it a hard time moving smoothly in the long PTFE tube, which it needs to go through to be able to reach the hotend.
Below, you can find some tips and tricks that will allow you to print TPU more consistently with a Bowden extruder:
- Reposition to extruder and shorten the length of the Bowden tube. Repositioning the extruder and bringing it closer to the hotend will allow you to use a shorter Bowden tube that will provide a straight path between the extruder and the hotend, reducing the chance of the filament getting stuck in the tube.
- Utilize TPU filament with a higher shore hardness value. The higher the shore hardness value of the TPU is, the less flexible it will be, which will drastically reduce the chance that it ends up getting stuck in the Bowden tube during movement.
- Use a 3D-printed direct-drive extruder mount to convert the Bowden extruder into a direct-drive one. While this solution may not exist for every 3D printer, it’s pretty straightforward to find such attachments for popular moddable printers such as the Ender 3 and the Ender 5, allowing you to turn the Bowden extruder into a makeshift direct-drive extruder and eliminate the Bowden tube.
As TPU is one of the more tricky filaments to print with successfully, the occurrence of issues, especially if it’s your first time trying TPU out, is definitely not surprising, with the problem of the filament ending up jamming the extruder being one of the more common ones.
To quickly recap, moving the filament around too much or too quickly can both contribute to the issue of TPU failing to extrude and cause the extruder to become jammed, where the former is a product of using a too high retraction distance, and the latter often stems from using a too high retraction speed, or print speed.
As a result, keeping the print speed, the retraction speed, and the retraction distance values as low as possible when printing TPU is always a good idea, as this will prevent any issues related to the movement of the filament in the extrusion assembly from occurring.
Mike started his 3D printing journey with the Anet A8 when it first came out back in 2017, and has been obsessed with 3D printers ever since. Nowadays, he primarily uses his Ender 3 to print functional parts that make his life more convenient whenever possible.