Intro to CAD and 3D printing
What you’ll learn
- What CAD is and which free tools to start with
- The sketch → extrude workflow
- How to design parts that fit and print well
CAD
CAD (computer-aided design) lets you design parts precisely on a computer. Good free starting points:
- Tinkercad: in the browser, builds parts from simple shapes. Ideal for beginners.
- Onshape (free plan) and FreeCAD: sketch-based “parametric” CAD used by engineers.
The basic workflow in sketch-based CAD:
- Sketch a 2D shape on a plane (rectangles, circles, lines) with exact dimensions.
- Extrude it into 3D (give it a thickness).
- Cut holes and pockets with more sketches.
- Fillet sharp edges to make them stronger and nicer to handle.
- Export as STL and slice it for your printer.
3D printing basics
- PLA is the easiest material: cheap, low warp, good for brackets and mounts.
- Layers are weakest between each other. Orient parts so the force doesn’t try to peel layers apart.
- Infill of 15–25% is plenty for most robot parts; use more walls for strength.
- Holes print slightly small. Add about 0.2–0.4 mm to hole diameters (an M3 screw hole: about 3.3–3.4 mm).
- Overhangs steeper than about 45° need supports.
Measure twice
Use calipers (about $10) to measure parts like motors and sensors before designing mounts for them. Print a small test piece before printing a big part.
Example: a sensor bracket
A 40 × 20 mm plate, 3 mm thick, with two 3.4 mm holes 30 mm apart to bolt onto the chassis, and a second plate at 90° with two holes matching the sensor’s mounting holes. Fillet the inside corner for strength. Print it flat on the large face.
Example: fixing a tight fit
A printed hole for an 8 mm shaft came out 7.7 mm. Increase the hole in the CAD file to 8.3 mm and reprint. Note the offset for next time: it’s a property of your printer.
Example: print time and cost
A 20 g PLA bracket at roughly $20 per kg of filament costs about $0.40 and prints in about 40 minutes.
First modelEasy
In Tinkercad, make a 50 × 30 × 3 mm plate with four 3.4 mm holes, 5 mm in from each corner.
Servo horn adapterMedium
Measure (or look up) an SG90 servo’s dimensions and design a simple mount that holds it on a robot’s chassis. Search for the SG90 datasheet: the body is roughly 23 × 12 mm with mounting tabs.
Make it strongerHard
A printed L-bracket snaps along a layer line at the corner. Give three design or print changes that would make it stronger. Print it on its side so layers run around the corner instead of across it; add a fillet or a triangular gusset in the corner; add more perimeters/walls and thicker material at the corner.
Quick check
Finished this lesson?