Not every problem in 3D printing will cause a catastrophic failure of your project. In some cases, the error manifests as minor blemishes and imperfections. 3D print zits are a typical example. You might still end up with a relatively solid 3D print, but it’s not going to look as good as you likely would have envisioned.
Undoubtedly 3d print zits and blobs are the cases. These are surface imperfections created by unwanted variations in filament extrusion. The good news is that you can likely avoid these defects by changing a few slicer settings.
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What Are Zits On 3D Prints?
Blobs or zits typically take the form of small bumps on the outer surface of 3d print. Upon closer inspection, you may notice that a single chunk or zit is exclusive to just a single layer. This should already clue you in the root cause of blobs and zits.
Another feature is that the blobs and zits are distributed almost uniformly across the entire outer surface. It implies that the surface defect is not just a one-off problem. There is likely a systemic problem in your 3d printer or slicer that is causing a reasonably consistent error.
There can be several possible causes for blobs or zits in your 3D print. However, all of them will result in inconsistent extrusion. Regardless, print quality will undoubtedly suffer when 3D printing blobs and zits are left uncontrolled.
What Causes Zits On My 3D Print?
As with most 3d printing issues, there can be several different but related causes for 3d print blobs.
Too much filament
In a way, blobs and zits are the opposite of layer gaps in 3d print. They represent spots where too much filament are extruded. If zits and blobs have become a common problem, you can try to keep a close on your 3D printer while it runs and identify when and where they occur.
Do zits and blobs appear at the point where a layer starts or stops? This means that there are short bursts of extra filament when the extruder starts or stops a layer. If this is the case, you likely need to refine your retraction settings.
Pressure is too high on the extruder
Too much pressure on the extruder will make it more likely to end up with excess filament in unwanted spots. This extra pressure can cause by several factors, including improper printing temperature, speed, and retraction setting.
Printing speed is too high
Printing at very high speed or extrusion multiplier settings can be a significant cause of blobs and zits. Higher print speed means that filament is delivered faster to the extruder and hot end. This causes undue pressure on the extruder and makes it harder to control the flow of molten filament.
The optimal printing speed will vary based on the 3d filament type you are working with and other settings such as the printing temperature. We suggest setting a default printing speed according to manufacturer recommendations and adjusting if necessary.
Retraction, coasting, and wiping settings
Retraction plays a massive role in potentially avoiding blobs and zits. However, unnecessary retraction can also cause them. The key here is to strike the perfect balance and to take advantage of coasting and wiping features.
The prevailing good practice to avoid zits and blobs is to retract only when necessary. Having no retraction is ideal because it ensures that there is constant and continuous extrusion of filament. However, your model may have significant gaps that the extruder needs to cross. In this case, enabling non-stationary extrusion will help avoid blobs at points where extrusion stops.
Avoiding retraction is even more critical if your 3d printer has a Bowden extruder. In a Bowden setup, retraction is made more complex by the extra distance between the extruder and nozzle. This makes retraction more disruptive if you aim to make extrusion as smooth and consistent as possible. Direct extruders are less problematic but still may not retract perfectly.
If retraction is necessary, make sure to dial in the optimal settings. The retraction distance defines how far the filament will pull back. Anywhere between 1 to 5 millimeters can work. The optimal location can vary based on your filament type and 3d printer settings. We recommend starting at the minimum set and increasing by 0.5-millimeter increments.
Retraction speed refers to how quickly the filament will be pulled back by the extruder. Too slow, and there may still be enough pressure in the extruder nozzle to cause blobs, zits, or string. Too fast, and there may be a delay when the printer needs to start to extrude again. The minimum retraction speed should be around 20 millimeters per second but can be increased up to 100 millimeters per second. It’s a good practice to start at the minimum value and increase by 20 mm/s increments.
Coasting is another feature worth exploring. When coasting is enabled, extrusion stops just before a layer is finished. This means that any built-up pressure in the extruder will cause the filament to ooze out so that you do not end up with zits where the layer terminates.
Wiping is only a slight variation to coasting that has the same goal. Instead of releasing built-up pressure on an empty spot, wiping adds to the filament that has already extruded.
Wiping is worth considering if you’re worried about seeing under-extrusion at the endpoints of a layer. Coasting and wiping settings can be refined to control the volume of filament that will be extruded solely by the built-up pressure in the nozzle.
Printing temperature is too high
An excessive printing temperature makes your filament behave more like a fluid. The melted plastic can more easily ooze out of the nozzle and cause 3D print zits or blobs.
You can consider reducing your printing temperature by increments of 5 C. This will make the melted filament less fluid and less prone to oozing out. However, shallow printing temperatures can also cause problems related to layer adhesion. You will likely also have to adjust the printing speed to account for the lower nozzle temperature.
Extruder pathing
Extruder pathing refers to controlling where the nozzle travels when doing an empty run. It helps to eliminate unnecessary retraction. If you can not stop it, you can reduce the number of times that the filament needs to retract. Improper extruder pathing will result in heavy retraction and a higher likelihood of zits and blobs.
Some slicers offer an option to “Retract only when crossing open spaces,” although the exact wording may vary from one slicer software to another. When this feature is enabled, retraction is no longer done when the print head movement crosses through internal spaces. This is less problematic as any zits, blobs, or strings will not be visible from the outside.
Simplify3D offers an alternative with the “Avoid outlines for travel movement” feature. When this feature is enabled, the travel path of the nozzle will be automatically altered so that it will never cross the outline perimeter of the print. If this is possible with your model, this means that you can finish the entire 3D print without having to use filament retraction. This powerful feature can help avoid zits and blobs among other extrusion-related issues.
How To Prevents Zits On 3D Prints?
The reasons listed above should already give you an idea of the measures you can take to avoid 3D print zits and blobs. Aside from changing a few 3D slicer settings, hardware tweaks can also influence print quality.
Clean your nozzle
Any dirt or residual filament on your nozzle can cause extrusion issues. This may not be apparent initially but will most certainly cause quality issues down the road.
In the case of 3d printing zits, any solid residue left inside the nozzle contributes to increasing the pressure of the extruder nozzle. It will more likely for the melted plastic to ooze out of the nozzle and create zits and blobs.
The best practice is to set regular schedules for cleaning your extruder nozzle. The easiest way to do this is to brush the interior of the nozzle with a metal-bristled brush. In case of heavy fouling, you may have to soak the nozzle in acetone for a couple of hours. It’s necessary if the filament residues in the nozzle have been burnt and solidified.
Keep your filament dry
Printing with filament saturated with moisture is probably one of the worst things you can do. Not only are you going to end up with lots of quality issues, but you can cause damage to the internal components of your extruder.
Detecting wet filament is easy. As wet filament enters the heating block, the moisture in the filament will start to boil and evaporate. This will create prominent popping and hissing sounds. You can expect many of your layers to have gaps or a pock-marked surface in terms of print quality because of the space that the moisture leaves as it evaporates.
Within the heating block, the evaporation of the moisture is more likely to cause your filament to form residues. As the residual filament builds up, it can cause clogs to increase the pressure in the extruder nozzle. A clogged nozzle will be very hard to achieve uniform extrusion and make 3d print zits and blobs more likely to form.
Printing with wet filament is so problematic that you’re better off stopping the print and starting over again.
To ensure that you’re printing with dry filament, always keep your filament in an airtight container with some desiccant. If necessary, you may dry your filament in a special filament desiccator. Drying the filament in an oven is also an option, but only if your range has reliable temperature controls.
Do a test print
Even with the best-laid plans, there are still many things that can go wrong with your 3d print. If you’re working on a massive project, it can lead to lots of wasted filament. If you’re unsure about your settings, the prudent thing to do would be to do a test print.
The ideal test print is a model that is small but has lots of different types of details. Some in the community refer to these test models as “torture tests.” Think of it as a calibration print before you go and spend an entire day printing your actual model.
The most popular torture test by far is the classic Benchy. This is a good choice for a test model if you’re dealing with zits and blobs as it has a relatively large smooth, and curved surface.
A test print should consume less than 20 grams’ worth of filament and print within an hour or less. Consider it an investment in your time and filament material that will keep you from wasting more of them down the road.
How To Remove Zits On 3D Prints?
Ideally, it would help tweak your 3d printer settings to avoid 3D print zits and blobs altogether. However, minor defects after printing can still be salvaged. Post-processing is a natural part of the 3D printing process.
The best and most straightforward method to deal with zits and blobs is to sand them smooth. Sanding removes any of the excess plastic on the 3d print, leaving a more unblemished surface. You can use different types of sandpaper with progressively increasing grit numbers. You can also set the Z-seam so that the seam position is at a less visible area.
Aside from eliminating zits and blobs, sanding will also remove visible traces of layer lines. This will leave you with an overall improved aesthetic. Polishing and painting generally result in vastly enhanced 3d print surfaces.
Summary
In the context of 3D printing defects, blobs and zits are pretty low in the hierarchy. They generally do not cause a 3d print to fail and can be remedied with some post-processing. However, they can still be a headache if you’re aiming to make your 3D print look as perfect as possible.
Zits and blobs can usually be traced to improper 3d printer settings that cause issues in extrusion. Fortunately, this also means that you should fix the problem with some changes in your slicer software settings. Dealing with zits and blobs is relatively easy after some experience with printing.
