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STL export and slicer setup

Summary

After completing all part bodies in FreeCAD, each body is exported as an STL file and imported into PrusaSlicer. Correct part orientation in the slicer is as important as the print profile settings — the arm shaft printed in the wrong orientation produces a structurally deficient part regardless of all other settings. This article covers export settings, the complete export list, and correct orientation for each part.

Concept

Why orientation is a separate decision from modelling orientation

FreeCAD models parts in a design coordinate system — the arm shaft might be modelled horizontally for convenience. PrusaSlicer prints in a physical coordinate system — the build plate is Z=0 and gravity is down. The correct print orientation for the arm shaft (vertical, motor head up) is a printing decision, not a modelling decision. The two orientations are often different. Every part must be explicitly oriented in the slicer before slicing.

Reference

FreeCAD STL export settings

Setting Value
Format STL
Units mm (verify — not inches)
Quality / Deviation 0.01 mm

Export list

Filename Body Qty to print Notes
Arm_Shaft.stl Arm 4 + 2 spares Same file for all copies
Arm_Tab.stl Arm Tab 8 Same file for all copies
Arm_Cover_Active.stl Arm Cover Active 4
Arm_Cover_Passive.stl Arm Cover Passive 4 PETG-CF — respirator
X_Body_PCCF_Base.stl X Body PCCF Base 3 Layers 2, 3, 4 — identical
X_Body_PETG_Bottom.stl X Body PETG Bottom 1 Layer 1 — impact face
X_Body_PETG_Top.stl X Body PETG Top 1 Layer 5 — features surface
Platform.stl Platform 1 Longest single print
Backplane.stl Backplane 1 Lattice — no supports
GPS_Camera_Bracket.stl GPS Camera Bracket 1
Camera_Tilt_Plate.stl Camera Tilt Plate 1
ASA_Bumper.stl ASA Bumper 4 + 4 spares
Sensor_Mast.stl Sensor Mast 1 (if fitting payload)

Correct orientation per part in PrusaSlicer

Part Print orientation Reason
Arm shaft Vertical — motor head up or down Layers perpendicular to bending load
Arm tab Flat / horizontal Large flat base, no strength orientation requirement
Arm cover active Flat Large flat part
Arm cover passive Flat Large flat part
X body PCCF layers Flat on build plate Maximum dimensional accuracy
X body PETG bottom Flat on build plate
X body PETG top Flat, face-up GX12 chimneys point downward into support
Platform Flat, face-up All features accessible; chimneys supported downward
Backplane Flat, face-up Lattice prints cleanly flat — no supports required
GPS camera bracket Flat
Camera tilt plate Flat
ASA bumpers Flat

PrusaSlicer import procedure

  1. Open PrusaSlicer.
  2. Select printer profile: PRUSA COREONE+.
  3. Select filament profile matching the part material.
  4. Drag and drop the STL file onto the build plate.
  5. Right-click part on build plate → Orient → Place on Face → select correct face.
  6. Verify orientation matches the table above.
  7. Apply print profile settings from print-profiles article.
  8. Slice and verify layer preview — check supports, infill, perimeter count.
  9. Export G-code.

Linux Flatpak specific notes

  • Macro path: ~/.var/app/org.freecad.FreeCAD/data/FreeCAD/Macro/
  • Sandbox file access (run once): flatpak override org.freecad.FreeCAD --filesystem=home
  • Sketcher visibility on dark themes: Preferences → Display → Colors → Sketcher → adjust

Procedure

Exporting a body from FreeCAD

  1. In the Model Tree, click the Body you want to export.
  2. Right-click → Export Mesh. (Alternative: File → Export with body selected.)
  3. In the dialog:
  4. Format: STL Mesh
  5. Units: mm (verify this is not showing inches)
  6. Deviation: 0.01 mm
  7. Save to your /stl/ output folder.
  8. Repeat for every body.
  9. Verify file sizes are non-zero and roughly proportional to part complexity.

Rationale

Why 0.01 mm deviation for STL export

STL format approximates curved surfaces with triangles. The deviation setting controls how closely the triangulation follows the true surface. At 0.01 mm deviation, the largest gap between a flat triangle and the true curved surface is 0.01 mm — well below the resolution of any FDM printer. Coarser settings (0.1 mm default) produce visible faceting on the arm shaft motor head curves and O-ring counterbores.

Why verify units at export

FreeCAD models in mm. Some FreeCAD installations default STL export to inches. An arm shaft exported in inches and imported into PrusaSlicer (which assumes mm) will appear 25.4× too large. Always verify the units field in the export dialog.

Connections

requires: - freecad-workbenches - print-profiles related: - coupon-validation - production-run-order leads_to: - production-run-order - airframe-integration