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.

Monotonic Top Layers on Right

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.

Left is a standard print, right is with ironing on

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

1. Assess Model Requirements:

   • Flat Surfaces: Prioritize monotonic order and ironing.

   • Curved Surfaces: Disable ironing; focus on layer thickness.

2. 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.

3. Validate with Test Prints:

   • Print calibration squares to check for pillowing or warping.

   • Test ironing on flat benchmarks (e.g., XYZ cubes).