Zits and blobs appear as irregular bumps or ridges on the surface of a 3D print.
The surface defect can ruin the quality of an object, especially if they appear on items designed for their aesthetic, like cosplay items or home decor.
We’ll cover seven easy fixes to prevent 3D print zits and blobs so you can get back to printing top-quality objects.
Let’s dive in.
What Causes and Blobs and Zits?
The most common cause of blobs and zits is too much filament accumulating on the print’s surface, also known as over-extrusion. Over-extrusion during the printing process creates a buildup of filament, creating the appearance of zits.
These print imperfections may also be called warts, bumps, or bubbles.
No matter the name, they result in finished prints that are less than ideal. Zits and blobs can ruin the print quality of 3D-printed objects.
Zits and Blobs can be caused by:
- Incorrect retraction and coasting settings
- Pressure in the extruder (over extrusion)
- The printing speed is too fast
- Printing at too high a temperature
- Not enough cooling
How to Fix 3D Print Zits and Blobs
There are several ways to fix and prevent zits and blobs in your 3D prints. To fix blobs and zits, you’ll need to clean your nozzle head, print with dry filament, and adjust your slicer settings.
By taking the time to calibrate your 3D printer, you can eliminate zits and blobs from your prints.
Lower Your Printing Temperature
Printing with a nozzle temperature that’s too high can cause over-extrusion. The blobs and zits form as excess filament oozes out of the extruder nozzle.
We recommend lowering your nozzle temperature in 5°C increments until you find an optimal print temperature.
Be careful not to lower the print temperature too much. Printing at temperatures that are too low can result in problems with layer adhesion.
You can also reference the manufacturer’s print temperature recommendation for the filament. Different filament brands perform better at different temperature settings.
Lower Your Print Speed
Printing at high speed can create zits and blobs, especially when combined with a high printing temperature. A high printing speed results in faster filament delivery to the hot end.
Higher printing speeds create extra pressure in the hot end and make it more difficult for your 3D printer to control filament flow.
We recommend decreasing the printing speed in 5mm/s increments and testing the results. Like printing temperature, it’s a good idea to reference the manufacturer’s recommended print speed.
Adjust Retraction Settings
Correctly setting your retraction speed and retraction distance helps mitigate the over-extrusion that causes zits and blobs in your 3D prints. The retraction settings tell the extruder to pull back the filament from the hot end and reduce pressure during critical times of the print (between layers and when traveling over empty spaces).
Enabling retraction helps prevent blobs and zits, especially those viable on a flat surface near a corner or round section of the object.
In our experience, a retraction distance of 1-5mm is ideal, with a retraction speed of 20mm/s to 75mm/s.
If you want to dial in your retraction settings, this Retraction Test on Thingiverse is a good start for a test print.
The retraction settings are one of the most challenging settings to calibrate. Take your time, and use the test print above until you find a combination of retraction speed and retraction distance that produce excellent results.
Excellent print quality is worth the effort.
Coasting is another Cura setting worth trying. The coasting settings tell your 3D printer to stop extruding just before a layer finishes printing.
Coasting releases built-up pressure by allowing the extra filament to ooze out at the end of the layer.
If your 3D print zits and blobs are especially noticeable at the Z seam, you’ll want to look at your coasting settings.
Cooling is imperative for achieving optimal FDM prints.
If cooling settings are set too low, the molten plastic will have the tendency to move around immediately after being dispensed. Without proper cooling, the molten plastic can ooze over the edge of the previous print creating various surface defects like zits and blobs.
If you think cooling is your issue, print several test prints, increasing the fan speed by 10% each time. Compare the test prints to see which cooling setting creates the best surface finish.
What happens if your fan is set to maximum speed?
If your fan is set to maximum speed and you’re still unable to cool the filament, you can always add a second fan or upgrade the existing fan.
Ambient air temperature may also play a role in cooling your 3D prints. If you’re printing in a warmer climate, you may need to add a couple of powerful fans to your 3D printer.
Wiping works by combining retraction and print head movement to “wipe” filament between layers.
You can enable wiping settings in Cura by clicking “Wipe Nozzle Between Layers.”
Wiping minimizes the start and stops between print layers, creating a more seamless transition.
Enabling wiping is usually used to eliminate Z seams created at a layer change. But it can also help to reduce the zits and blobs that form when retraction occurs at the same spot on every layer.
If you enable wiping in Cura, we recommend looking at the “Outer Wall Wipe Distance.” We have it set to 0.4 mm on our Ender 3 V2, which works wonders.
Clean Your Nozzle
Sometimes zits and blobs result from a buildup of dirt or residual filament within the nozzle. The debris can cause a buildup of pressure in the nozzle, resulting in extrusion issues.
If the pressure in the print head rises, the nozzle will “burp” out the extra pressure, forming unwanted zits and blobs.
We recommend heating the hot end to normal printing temperatures and cleaning the nozzle with a calibrated needle. Another option is to simply replace the nozzle after several months of printing.
Keep Your Filament Dry
Printing with wet filament is one of the worst things you can do when you print.
Excess moisture might be your issue if you opened your filament spool long ago.
Plastic (especially PLA and PETG) absorbs water, causing the filament to swell. When the wet filament is heated, the excess filament evaporates into steam inside the extruder nozzle.
As the water evaporates, the vapor pressure builds in the nozzle. The excess pressure can result in over-extrusion, causing blobs and zits.
Additionally, the steam created by the water can exit the nozzle, splashing filament on your 3D print. When the filament cools, it forms raised bubbles on your print.
It’s easy to test if your filament is wet.
Listen closely as your printer begins printing the first layer to detect wet filament. You know you have a wet filament if you hear popping or hissing sounds while printing.
The sounds are the water heating up and evaporating.
If you hear these sounds, stop printing immediately. Either dry out your filament or grab a dry filament to use with your 3D printer.
It’s essential to properly store your filament to prevent it from absorbing moisture and becoming wet. We recommend storing your filament with desiccant, which helps to absorb airborne moisture before it infiltrates your printing filament.
If you notice that your filament is wet, you can dry it in a dehydrating machine or a special filament dryer.
How to Remove Zits From 3D Prints
Following the recommendations above can help eliminate zits and blobs from your 3D prints.
But how do you remove 3D print zits from your finished objects?
The best way to remove zits and blobs from finished prints is to sand them. Sanding your printed objects can remove zits and create a smooth finish on your 3D prints.