FDM 3D printing design check
FDM (also called FFF) melts filament and lays it down layer by layer. Most problems come from overhangs, long bridges, walls thinner than the nozzle can follow and the weak bond between layers. These are the limits a check looks at.
The limits that matter
| What | Typical limit used here | Why it matters |
|---|---|---|
| Overhang | steeper than 45° from vertical needs support | filament has nothing to rest on and droops |
| Bridge | up to 10 mm without support | longer spans sag in the middle |
| Wall | at least 2 nozzle diameters (0.8 mm with a 0.4 mm nozzle) | a thinner wall cannot hold two perimeters and is weak or missing |
| Clearance between moving parts | about 0.3 mm (working assumption) | less than that fuses the parts together |
| Strength across layers | about 85 % of in-layer strength for PLA, 70 % for PETG (working assumptions) | a part loaded across layers breaks at the layer line |
How to fix the common problems
- Choose the orientation first. It sets support, surface quality and which direction is weakest. Compare at least three positions.
- Chamfer instead of overhang: a 45° chamfer prints without support where a 90° ledge would not.
- Split large parts that exceed the first-layer size or warp on the bed.
- Keep loads along the layers, not across them, or use a tougher material or continuous fiber where stiffness matters.
What Dokimion checks for FDM
The check slices the mesh as a slicer would, compares each layer with the one below and reports support and bridges, thin walls and features thinner than the nozzle or layer, first-layer area and cross-section jumps for PLA, PETG, ASA, ABS and PA6-CF. It ends with a score from A to E (see the Kolesar Score), three suggested positions and a cost estimate per part.
Limits depend on the printer, nozzle and material. Treat them as a starting point and let the report show the source of every number.
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