Documentation
Designing for real-world fit
Tolerances, clearances, wall thickness and the dimensions a printer can hold.
Tolerances and clearances
A filament printer is not a milling machine. A well-tuned one holds about 0.2 mm either way, so two parts that must fit need a gap designed in:
| Fit | Gap per side | Used for |
|---|---|---|
| Tight or press fit | 0.1 to 0.15 mm | Snap joints, bearing seats |
| Sliding fit | 0.2 to 0.3 mm | A lid on a box, a drawer in a slot |
| Loose or clearance fit | 0.3 to 0.5 mm | Cables through holes, screw clearance |
Expose the clearance as a parameter, so a maker tunes it for their own printer:
param clearance: float = 0.3 [0.1:0.5:0.05] "Fit clearance (mm)"Wall thickness
The thinnest wall a printer makes well depends on its nozzle:
| Nozzle | Thinnest wall | Recommended |
|---|---|---|
| 0.4 mm | 0.8 mm (two perimeters) | 1.2 to 1.6 mm |
| 0.6 mm | 1.2 mm | 1.8 mm |
Give the wall parameter a floor the printer can make:
param wall: float = 2.0 [1.2:6:0.2] "Wall thickness (mm)"Screw holes
A printed hole comes out smaller than drawn, because the plastic pulls inward as it cools. Add 0.2 to 0.3 mm to the radius:
| Screw | Nominal | Hole to draw |
|---|---|---|
| M3 | 3.0 mm | 3.4 mm |
| M4 | 4.0 mm | 4.4 mm |
| M5 | 5.0 mm | 5.4 mm |
| #6-32 | 3.5 mm | 3.9 mm |
Overhangs and support
A filament printer bridges overhangs up to about 45 degrees without support. Design with that in mind:
- Chamfer an edge at 45 degrees instead of leaving a flat overhang.
- Draw a horizontal hole as a teardrop, so its top does not sag.
- Put the largest flat face on the bed; it decides the orientation.
Layer height
A vertical dimension lands on a layer. With 0.2 mm layers, a feature drawn 5.1 mm tall prints as 5.0 or 5.2 mm. Draw heights that matter as multiples of the usual layer heights, 0.1, 0.15 or 0.2 mm.