❌ Layer lines are clearly visible in FDM printing, so the surface is not perfectly smooth.
❌ Not all parts can be printed with very fine geometries as is possible with SLA or SLS.
❌ Additional post-processing (sanding, chemical smoothing, or painting) may be required to achieve an aesthetically pleasing finish.

❌ Interlayer adhesion – printed parts can be weaker at the layer interfaces, especially under loads oriented unfavorably to the print direction.
❌ Anisotropy of plastics – parts are not equally strong in all directions; loads perpendicular to the layer stacking are particularly critical.
❌ Incorrect print settings can cause voids/gaps between layers, reducing mechanical properties.

❌ FDM is not the fastest 3D printing method, especially when very high resolution and small layer heights are required.
❌ SLA and SLS can be more efficient for producing many small parts at once because they don’t rely on a single moving extruder.
❌ Large or complex prints can take hours or even days, depending on chosen layer height and speed.

❌ Some geometries cannot be printed without supports, especially with many overhangs or suspended features.
❌ Supports can leave unwanted surface marks, even after removal.
❌ Non-soluble supports must be removed mechanically, which can be challenging for fine details.

❌ Incorrect extruder temperatures can cause defects, for example:
    • Over-extrusion – too much plastic, rough surfaces.
    • Under-extrusion – too little plastic, brittle layers.
❌ ABS and some other plastics require an enclosed chamber to avoid layer separation (warping).
❌ Thermal expansion can cause dimensional changes, making parts less accurate.

❌ FDM is not the most precise technology – dimensional tolerance can be ±0.1 mm or higher.
❌ Larger parts may warp if not properly anchored to the build plate.
❌ Not all geometries print accurately, especially very thin walls or ultra-small features.