Top/Bottom Layers
Top and bottom layers define the external surfaces of 3D-printed parts, influencing aesthetics, structural integrity, and functionality. These fully dense layers bridge over infill and provide a foundation for subsequent layers. Proper configuration minimizes defects like pillowing, ensures dimensional accuracy, and enhances surface finish.
Top/Bottom Thickness Fundamentals
Thickness Calculation
Layer Height Dependency: Thickness is a multiple of layer height. For example, a 0.2mm layer height requires 5 layers to achieve 1mm thickness.
Minimum Recommendations:
Top Layers: 1mm minimum (e.g., 5 layers at 0.2mm) to prevent pillowing (dimpled surfaces caused by sagging over sparse infill).
Bottom Layers: 0.6mm minimum (e.g., 3 layers at 0.2mm) for adhesion and stability.
Adjustments for Infill Density
Low Infill (≤15%): Increase top layers (e.g., 6–8 layers) to compensate for reduced support depending on part geometry.
High Infill (≥30%): Fewer top layers (e.g., 4–5 layers) suffice due to dense underlying structure.
Note: Round thickness to the nearest layer height increment (e.g., 0.9mm for 0.3mm layers instead of 0.8mm).
Advanced Top/Bottom Layer Settings
Monotonic Order
Function: Forces lines to print in a single direction (e.g., left-to-right) for uniform overlap, eliminating inconsistent surface textures.
Benefits: Reduces bulges and improves flat surface quality.
Drawbacks: Slightly increases print time
The image below shows a print on the left without checking Monotonic Top/Bottom Order, and the right is with it checked on.
Ironing
Process: The nozzle reheats and smooths the top layer without extruding filament.
Applications: Ideal for flat surfaces (e.g., tabletops, enclosures) requiring a polished finish.
Limitations: Ineffective on curved surfaces; requires precise calibration of ironing speed, flow rate, and temperature.
Line Directions
Impact: Aligning top/bottom lines with part geometry (e.g., 45°/-45° crosshatch) reduces visible seams and improves strength.
Optimization: Adjust angles to minimize bridging gaps or align with load-bearing axes.
Troubleshooting Common Issues
Pillowing (Dimpled Top Surfaces)
Causes: Insufficient top layers, low infill density, or excessive cooling.
Solutions:
Increase top layers to 1.2–1.5mm.
Raise infill density to 20–30% for better bridging support.
Reduce part-cooling fan speed for slower solidification.
Warped Bottom Layers
Causes: Poor bed adhesion, uneven heating, or insufficient bottom layers.
Solutions:
Increase bottom layers to 0.8–1.0mm.
Use adhesives (e.g., glue stick, Magigoo, PEI sheets) and ensure bed leveling.
Ironing Artifacts
Over-Melting: Lower ironing temperature or reduce flow rate.
Incomplete Smoothing: Increase ironing passes or slow movement speed.
Practical Workflow for Configuration
Assess Model Requirements:
Flat Surfaces: Prioritize monotonic order and ironing.
Curved Surfaces: Disable ironing; focus on layer thickness.
Calibrate Settings:
Top Layers: Start at 1mm (5 layers at 0.2mm); adjust based on infill density.
Bottom Layers: Use 0.6–0.8mm (3–4 layers at 0.2mm) for adhesion.
Validate with Test Prints:
Print calibration squares to check for pillowing or warping.
Test ironing on flat benchmarks (e.g., XYZ cubes).
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