Blobs or Zits
What Is It?
Blobs or Zits are the tiny dots on your print's surface and directly affect its overall quality and appearance. These are often the result of incorrect retraction settings or high printing temperature and negatively affect the surface finish of your 3D printed part.
Sometimes, you can easily remove them with sanding, but big blobs can be challenging to remove and may leave an impression on your parts. For this reason, it's best to tune your printer to not create them in the first place rather than try to remove them through post-processing.
What to Check?
- Printing Temperature
- Retraction settings
- Z-Seam settings
How to Fix It?
Print at low temperatures
Printing at high temperatures will cause your filament to melt more than necessary and slightly increase its viscosity. Due to this, the filament material can ooze out of the nozzle during travel moves. A high printing temperature might cause more filament to be extruded from the nozzle at the start of a printing point, leading to blobs on the print's surface.
If your extrusion settings are neatly calibrated, you can try a lower printing temperature to reduce the chances of blobs occurring on your 3D prints. You can try reducing it in 5 °C intervals till there are no blobs on your parts.
Calibrate Retraction Settings
Incorrect retraction settings can lead to stringing and oozing filament from the nozzle. These settings are one of the significant reasons behind blobs on your print's surface. You can refer to our section on the Stringing issues to understand it in detail and fix your printer's calibration settings.
Blobs often occur at the start and the end point of layers. You can quickly identify these as z-seam blobs that will likely be in a straight line or have a pattern. You can quickly adjust your layer's start and end point using your slicer settings and effectively eliminate the blobs on your print's surface.
In Cura, you can specify the z-seam settings to inform the hot end regarding the print's start points. You can either align the z-seam with the sharpest corner or randomly distribute the starting points evenly to distribute the layer starting points. Both these values can visibly reduce the blobs on your print's surface and improve your print quality.
Calibrate Linear Advance (Experimental)
Linear advance or Pressure advance is similar to the coasting setting applied within your slicer. But, it's slightly more elaborate and is directly adjusted in your printer's firmware for more accurate and predictable results.
It's an easy but involving calibration process, and it's better to refer to Marlin and Klipper's guides on linear advance calibration. Once you set it up alright, you can expect a significant improvement in your print quality and a reduction in the bulging edges or corners in your 3D prints.