🖨️ 3D Printing & CAD Basics

What you’ll learn

1. It's a Hot Glue RobotDescribe FDM printing concretely as a hot glue gun on a robot, and state the two clauses — fuse while hot, shrink while cooling — that govern everything downstream.A printer pulls plastic filament into a heated nozzle, squeezes it out of a hole typically 0.3–1.0 mm across while moving in a plane, then steps up a fraction of a millimetre and draws again on top. A printed object is therefore not plastic in a shape — it's a few thousand small welds in a shape, each one's quality decided by how hot the plastic was on arrival and how fast it cooled.
2. The Weld You Can't SeeExplain anisotropy as partial layer welding, and treat part orientation on the bed as a structural decision.Printed parts split between layers rather than tearing through plastic, because each layer is a partial weld made before the surface below cooled too far to fuse. Published Z-strength reductions vary from roughly 25% to 80% across studies, so trust the direction of the effect rather than any single number. Orienting a part so load runs along the beads buys more strength than any upgrade you can buy.
3. Everything ShrinksExplain warping as differential shrinkage, and control it through adhesion and temperature difference rather than luck.Each layer arrives hot and immediately begins contracting while welded to cooled layers that have already finished shrinking, putting the part in tension that concentrates at corners. The cures are only ever two: more adhesion (a squished first layer, a clean bed, a brim or raft, a heated bed) or a smaller temperature difference (an enclosure). PLA barely shrinks and prints in a normal room; ABS shrinks hard and wants a 60–70 °C chamber.
4. Gravity Doesn't Wait for the Plastic to CoolDerive the 45° overhang rule from layer height and extrusion width, and rank orientation and design above supports.The real question is what fraction of each bead lands on the layer below: step = layer height × tan(angle), supported fraction = 1 − step/width. At 0.2 mm and 0.4 mm that gives exactly 50% support at 45° and zero at 63.4° — so the famous rule is a ratio you own, not a law you memorise. Bridges work because a strand pulled between two anchors sets under tension, which is why teardropping a hole converts an impossible overhang into an easy one.
5. CAD Is a Recipe, Not a SculptureWork parametrically — sketch, constrain, extrude — and explain why a constrained model survives change while a mesh cannot.Mechanical CAD is closer to programming than to sculpting: you write a recipe and the software produces the shape. Constraints record intent rather than coordinates, so when the 8 mm bolt becomes a 10 mm bolt the whole model re-runs correctly. Exporting to STL discards all of it, leaving triangles with no dimensions — which is why an STL is an output, like a PDF, and the CAD source is the thing worth keeping.
6. Designing for the MachineDesign for the process: measure your own clearances, anticipate undersized holes, and keep the machine in mind while drawing.In CAD 10 = 10, but two objects can't share space, so assemblies need deliberate clearance — and since the right figure depends on your machine, one test piece with 0.1–0.5 mm steps replaces guessing forever. Holes print undersized because the bead compresses on the inside of a curve and hot plastic closes inward as it cools, while bosses shrink too, so the error stacks. Designing for printing isn't extra work; it's asking about orientation, overhangs, fits and wall thickness while you draw.
7. The Slicer Makes the Real DecisionsRead the slicer as the place every quality decision is actually made, and choose perimeters over infill for strength.The slicer turns a mesh into G-code and decides perimeters, infill, support, speed and flow before the machine moves — the printer merely obeys a text file. Strength lives in the perimeters, because bending stress concentrates at the surface exactly as it does in a scaffold pole, so extra walls beat extra infill per gram and per minute. Layer height is a real trade: it roughly scales print time, and it also moves the overhang limit, because that limit is a ratio of layer height to bead width.
8. Choosing a PlasticChoose filament by glass transition rather than melting point, and assess PLA's biodegradability honestly.Glass transition — where a polymer goes soft while still solid — decides whether a part survives: PLA's 60–65 °C is why phone mounts droop in hot cars, well below its 150–160 °C melting point. PETG is PET modified with glycol to disrupt crystallinity, buying toughness and heat tolerance; ABS reaches about 105 °C but warps hard and needs an enclosure. PLA composts meaningfully only at around 58 °C in an industrial facility, taking close to three decades in home compost or soil.
9. When It Fails — and What This Is Actually ForDiagnose print failures back to fusing or cooling, and judge honestly what the technology is and isn't for.Every common failure reduces to one of the two clauses: peeling and warping are shrinkage beating adhesion, layer splits and drooping overhangs are plastic that didn't fuse or wasn't supported while soft, and tight holes are a shrinkage bias to design around rather than a fault to fix. The technology is poor at mass production and unmatched at two things — geometry no mould can make, and iteration fast enough that being wrong became cheap.

Questions this course answers

Grounded in trusted sources

• Fused filament fabrication — nozzle diameters 0.3–1.0 mm, thermal control of deposited material, PLA at room temperature (18–25 °C) vs ABS chamber 60–70 °C: https://en.wikipedia.org/wiki/Fused_filament_fabrication
• Polylactic acid — glass transition 60–65 °C, melting point 150–160 °C, industrial composting at 58 °C (~half in 60 days), ~3 decades in home compost or soil, poor marine disintegration: https://en.wikipedia.org/wiki/Polylactic_acid
• Acrylonitrile butadiene styrene — glass transition ≈105 °C; warping due to shrinkage on cooling; enclosure, heated bed, brim/raft mitigations: https://en.wikipedia.org/wiki/Acrylonitrile_butadiene_styrene
• Polyethylene terephthalate — PET glass transition 67–81 °C, melting point >250 °C; PETG glycol-modified with CHDM to disrupt crystallinity: https://en.wikipedia.org/wiki/Polyethylene_terephthalate
• Anisotropy of FDM parts — reported Z-direction strength reductions vary widely by source (roughly 25%–80%); see e.g. Protolabs Network, 'How does part orientation affect a 3D print?': https://www.hubs.com/knowledge-base/how-does-part-orientation-affect-3d-print/
• The 45° overhang figures in this course are derived arithmetically from a 0.2 mm layer height and 0.4 mm extrusion width (supported fraction = 1 − (h·tan A)/w), not taken from a published table.

Every Wunder lesson is built from real, reputable sources — never invented.

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