Consistent extrusion is one of the essentials of successful 3D printing, as the consistency of the extrusion practically determines whether the 3D model you’re seeing on your screen will be the same as the object that you are getting out of the 3D printing process, whether it’s the details of the model or the dimension.
On the other hand, achieving consistent extrusion is more complicated than it sounds, as extrusion consistency relies on many factors ranging from the smoothness of the printhead movement to the stability of the hotend temperature, meaning that every single part of the 3D printer needs to be functioning correctly for the extrusion to be optimal.
Today, we will be talking about one of the issues that can introduce inconsistencies to the extrusion, known as under-extrusion after retraction, in specific, which we can quickly explain as the filament coming out of the nozzle being less than it actually should be whenever the 3D printer retracts the filament back to prevent the filament from oozing.
So, what can cause your 3D printer to under-extrude after a retraction?
The primary culprit behind the occurrence of under-extrusion after a retraction is the usage of a Retraction Distance value that is way too high, which contributes to under-extrusion taking place by creating problems such as filament grinding and filament jamming.
Next up, we will examine the factors that can cause under-extrusion after retraction in greater detail, find out how to fix the under-extrusion after retraction problem, and finally, quickly troubleshoot the two similar issues of under-extrusion at the start of a layer, and under-extrusion halfway through a print.
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What Can Cause Underextrusion After Retraction?
While the under-extrusion after retraction problem is one that can easily ruin your prints, especially when the under-extrusion is severe, the culprit behind it is, fortunately, pretty straightforward, unlike most issues where there are multiple potential culprits.
Over-retraction, which is a term that refers to the filament being retracted way more than optimal, is the factor behind the occurrence of the under-extrusion after retraction issue, primarily stemming from the usage of a Retraction Distance value that is too high.
With a Retraction Distance too great, the filament gets pulled far too back with each retraction, which eventually causes the same exact portion of the filament to come into contact with the extruder gears multiple times.
The repeated contact between the extruder gears and the filament eventually causes the filament to become worn down, with the extruder gears stripping bits off the filament as they grip it, which creates the issue known as filament grinding, where parts of the filament end up becoming thinner due than normal.
When the 3D printer attempts to extrude these thinner portions of the filament, under-extrusion naturally occurs due to the lack of material available, as the 3D printer cannot distinguish the difference between an intact portion of the filament and a thinned-out one.
While rarer, it’s also worth mentioning that a Retraction Speed value that is too high can also contribute to under-extrusion after retraction in some cases, as moving the filament at speeds that are way too high will also increase the likelihood of the extruder gears grinding the filament, even in cases where the particular portion of the filament does not come into contact with the extruder gears multiple times.
How to Fix the Issue of Underextrusion After Retraction?
Now that we know the culprit behind the issue, fixing the problem of under-extrusion after retraction is relatively straightforward, as all that is required is the modification of a few parameters and some testing to ensure that the problem doesn’t occur again.
Below are the solutions we recommend applying to fix the issue of under extrusion after retraction:
- Decrease the Retraction Distance value. For the process of correcting the Retraction Distance, our recommendation would be to reduce the value by 1 millimeter in each iteration and to run a test print after each modification until the issue is resolved.
- Reduce the Retraction Speed value. When reducing the Retraction Speed, we recommend decrementing the value by 5 mm/s in each step and testing, which will ensure that the value doesn’t get way too low and counteract the benefits gained by retraction as a result.
- Increase the Retraction Extra Prime Amount value. To set the Retraction Extra Prime Amount parameter to the optimal figure, we would recommend increasing the value by 1 mm^3 at a time and running tests to ensure that over-extrusion does not occur after a retraction as a result of increasing the amount of primed filament.
Underextrusion Halfway Through the Print – What to Do?
In some cases, it’s possible for under-extrusion to take place at a particular point of the 3D printing process, such as when the print reaches the halfway mark, and while the issue remains the same, the culprit behind it becomes entirely different in this case.
The issue that is most likely to cause your 3D printer to under-extrude halfway through the print is heat creep, which is a problem where heat generated by the heater block ends up traveling further up the hotend, prematurely melting the filament before it reaches the suitable area (known as the hot zone) for it to melt.
As the problem is purely temperature related, decreasing the print temperature, lowering the distance of retractions (as a retraction can pull hot filament into the cold zone), increasing the print speed, and increasing the hotend fan speed can all be viable solutions to the issue of under-extrusion halfway through the print.
Underextrusion At the Start of a Layer – What to Do?
A similar but different issue is the occurrence of under-extrusion at the start of each layer, which will also have adverse effects on your 3D printed models, just as any other form of under-extrusion.
Below, you can find our recommendations to fix the issue of under-extrusion at the start of a layer:
- Reduce the Retraction Distance value.
- Increase the Retraction Extra Prime Amount value.
- Disable the Retract at Layer Change option in Cura.
- Correctly calibrate the E-step value.
- Lower the Print Speed value.
While the list above is not an exhaustive one by any means, it covers the fixes for the most common culprits that can create the issue of under-extrusion that occurs whenever the 3D printer starts printing a layer for the first time.
Even though under-extrusion after retraction can be a critical issue that requires solving as soon as possible, depending on the severity of the under-extrusion, finding the culprit behind it not being complex makes the solution relatively straightforward and effortless to apply.
To quickly recap, over-retraction, which is caused by a Retraction Distance value that is too high, is the primary culprit behind under-extrusion taking place after a retraction, as pulling a large portion of the filament back after each retraction eventually causes the extruder gears to strip off bits of filament that is overly exposed to retraction, creating the issue known as filament grinding.
While the best way to fix the issue at hand, in this case, is to correct the Retraction Distance value, reducing the Retraction Speed value to prevent the extruder from grinding the filament, or increasing the Retraction Extra Prime Amount value, which prompts the 3D printer to prime an extra length of filament to compensate for any potential losses during retraction, can also be helpful.
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.