Phase 3: Make it Move

"When your print has moving parts, you're not just making objects—you're engineering machines."

What You'll Learn

Welcome to the deep end. Now you're designing things with multiple parts that move, snap together, hinge, rotate, or assemble. This is where 3D printing gets seriously cool and seriously challenging.

You'll learn to think about clearance (space between moving parts), friction (too much = stuck, too little = wobbly), orientation (how you print affects how strong joints are), and strength direction (layers can separate if stressed the wrong way). These are the same concepts real engineers use for phone cases, car parts, and spacecraft.

This phase takes time—not because you're slow, but because mechanical design requires experimentation. Expect failures. Embrace them. Every broken hinge teaches you something.

Core Skills

• [ ] Design parts that fit together with intentional gaps for movement
• [ ] Create living hinges (thin flexible connections that bend)
• [ ] Design snap-fit connections that click together satisfyingly
• [ ] Understand print-in-place vs. assemble-after-printing tradeoffs
• [ ] Choose print orientation based on stress direction and joint strength
• [ ] Calculate clearances for rotating parts (usually 0.3-0.5mm minimum)
• [ ] Test mechanical concepts with small prototypes before full prints
• [ ] Diagnose why mechanical parts fail (tolerance? orientation? material?)

Suggested Projects

1. Hinged Box - A container with a lid attached by a living hinge. Teaches thin-wall design and flex properties. Start with a simple rectangular box.

2. Snap-Fit Lid - A lid that clicks onto a container with satisfying resistance. Teaches clip design, flex tolerance, and the joy of a perfect "snap."

3. Two-Part Nameplate Stand - A base and vertical holder that slide or snap together. Teaches assembly design and stable connections.

4. Simple Gears or Fidget Spinner - Start with a pre-made design, print it, then modify parameters. Teaches rotational clearance and bearing surfaces.

Success Criteria

You've completed this phase when you can:

• Design a hinge that flexes 90 degrees without breaking (after a few tries)
• Create a snap-fit connection that clicks together and can be separated without breaking
• Explain why you printed something in a specific orientation for strength
• Troubleshoot a mechanical failure: "It broke because layers separated under stress" or "Too tight—needs more clearance"
• Successfully complete a multi-part assembly that moves as designed

Tips & Tricks

Living hinges need the right thickness: Too thick = won't flex. Too thin = breaks immediately. Sweet spot for PLA is usually 0.6-1.0mm. Print tests!

Orientation is critical for hinges: Print hinges so the flex happens across layers, not along them. Layers that peel apart = instant failure.

The snap-fit formula: Design the clip to flex outward about 20-30% of its thickness. Too much = breaks, too little = doesn't hold.

Print-in-place is impressive but risky: Parts printed already assembled (like chain links) look amazing but need perfect tolerances. Better to master assemble-after-printing first.

Clearance for rotation: Spinning parts need more gap than sliding parts. Try 0.4-0.5mm minimum for gears or bearings.

Support material is sometimes worth it: If a part absolutely needs a weird angle, don't fight it—add supports. Your time is valuable.

Test one joint at a time: Designing a 4-part box? Print just two parts first to test the connection. Don't print all four and discover the snap-fit doesn't work.

Easter Egg 🥚

Master challenge: Design a print-in-place chain with at least 5 links that are already connected when the print finishes. No assembly required. This requires precise clearance—usually 0.3-0.4mm gaps between link layers. When you nail it, you'll feel like a wizard.

Remember: Professional engineers test ideas with prototypes. You're not "wasting" filament on tests—you're learning faster than trial-and-error on full builds. That's smart engineering.