Design rules for print-ready parts (FDM)
A model that looks fine on screen can fail on the bed. These are the rules SpeakCAD applies by default, and the reasoning behind them, so you know what to ask for when you need something different.Wall thickness
An FDM nozzle lays lines about 0.4 to 0.45 mm wide. Walls should be a multiple of that: 0.8 mm (two lines) is fragile, 1.2 mm is the practical minimum, 1.6 to 2.4 mm is right for anything structural. SpeakCAD defaults to 1.2 mm on decorative parts and 1.6 mm or more on brackets and enclosures.
Overhangs and bridges
Material needs something under it. Angles up to 45° from vertical print cleanly; beyond that the surface degrades and supports are needed. A 45° chamfer under a ledge replaces a support. Bridges (flat spans between two walls) work up to about 40 mm.
Holes and pegs
Horizontal holes print undersized by 0.2 to 0.4 mm because the extruded line bulges inward. Vertical holes are truer. Pegs print slightly oversized. Design the clearance in: 0.2 mm for a press fit, 0.4 to 0.6 mm for a free fit. Say "press fit" or "sliding fit" in SpeakCAD and the right allowance is applied.
First layer and elephant's foot
The first layer is squished for adhesion, so the bottom edge bulges outward by 0.1 to 0.3 mm. A 0.5 mm chamfer at the base hides it and keeps lids and stacking parts fitting.
Orientation and strength
Layers are the weak direction. Orient the part so the load runs along the layers, not across them, and add fillets at inside corners where cracks start. Hooks and clips should be printed lying down so the flex runs along the layer lines.
Small features
Text and details under 0.8 mm wide disappear. Raised text 1 to 1.5 mm high and at least 1 mm stroke width prints well; engraved text should be at least 0.6 mm deep.
Floating and thin geometry
Every piece must connect to the base; an island prints as a blob of spaghetti. SpeakCAD wraps the part in a single solid and rests it on the bed so that never happens.
- 1Give the part a flat basePick the face that sits on the bed and keep it flat; it prints without supports and sticks well.
- 2Respect minimum walls1.2 mm walls (three 0.4 mm lines) for light parts, 1.6 to 2.4 mm for parts that take load.
- 3Control overhangsKeep overhangs under 45°, or turn them into chamfers; bridges under 40 mm print fine, longer ones sag.
- 4Size holes with tolerancePrinted holes come out small: add 0.2 to 0.4 mm to the diameter, or ask for the fit type.
- 5Chamfer the bottom edgeA 0.5 mm chamfer at the bed contact avoids the elephant's-foot bulge and lets parts fit.