The Battle Against Spots: A Practical Guide to Perfect 3D Printing
There’s nothing more frustrating than carefully setting up a 3D print, only to find unsightly, unexpected chunks of plastic appearing on an otherwise perfect surface. These undesirable flaws are often called "spot" or "acne," A promising prototype or stunning model can be turned into an amateurish mess. But don’t be afraid! Spotting is a common and often solvable problem plaguing the field of FDM (fused deposition modeling) 3D printing. This guide takes an in-depth look at what causes these pesky spots and provides actionable steps to eliminate them, helping you achieve consistently smooth, professional-looking prints at home or in the lab.
What exactly are spots and why do they appear?
Spots (sometimes called pimples) are small bumps of excess material that usually appear at the beginning or end of the perimeter of the layer, or appear randomly on the surface. This occurs when molten plastic inadvertently seeps out of the nozzle and settles where it shouldn’t. Unlike stringiness (called filaments), spots are physically prominent localized deposits. They will destroy the appearance, affect dimensional accuracy, and even cause printing failure in severe cases.
Root cause – usually related to flow control:
- Bad retraction settings: This is culprit. During non-extrusion movements (such as movement between parts or layer changes), retraction pulls the filament slightly back into the nozzle. If the retraction distance is too short, or the speed is too slow, pressure will build up in the molten plastic, causing it to ooze ("Dribbling") exits prematurely when printing resumes, forming spots at the starting point.
- Printing temperature is too high: Filament that is extruded too hot will become too liquid. This makes control more difficult by retraction alone, increases the chance of leakage during travel movements and results in spots at the restart point.
- slide: While gliding (stop extrusion slightly before the end of the perimeter line) able Reduces leakage, which can result in under-starting if set too aggressively Next lines, creating pressure that creates spots when extrusion is restarted.
- High travel speed: Moving quickly between dots can pull the print head violently, causing the molten filaments attached to the nozzle to be flung randomly onto the model surface.
- Hygroscopic filament: Filaments such as PLA, nylon or PETG readily absorb moisture from the air. This water will boil violently when extruded, creating a large amount of residual steam that will blow small water droplets onto the printing surface. This often manifests itself as
