Week 2 – Computer-Controlled Cutting
Assignment Brief
Design, laser-cut, and assemble a parametric construction kit. Document kerf, joints, and tolerances. Optional: vinyl cut a design.
Project: Halftone Portrait Stand
Laser-engraved Leonardo da Vinci portrait on acrylic, with a parametric cardboard stand. Initial cube design failed under the acrylic's weight—pivoted to a simpler back-support stand. First encounter with structural design constraints and material properties.
Laser Engraving: Halftone Portrait
Material: 6mm dark tone acrylic
Image: Leonardo da Vinci self-portrait (halftone conversion)
Process: Raster engraving at 75W CO2 laser
- Converted grayscale portrait to halftone pattern (variable dot size for tonal depth)
- Test cuts on scrap acrylic to dial in power/speed (5.39.61 settings on PLSB.75 system)
- Engraved ~12cm × 12cm portrait area
- Result: Frost-white engraving with good contrast on clear acrylic
Parametric Stand Design (FreeCAD)
Designed a press-fit cardboard stand to hold the acrylic portrait vertically. This was my first attempt at parametric CAD—chose FreeCAD before switching to Fusion 360 in later weeks.
Design Intent (Failed)
- Original plan: Cube frame kit with 4 corner posts and cross-braces
- Material: 4mm corrugated cardboard
- Joints: Finger joints with kerf compensation (0.2mm offset)
- Parametric variables: Material thickness, joint spacing, overall dimensions
What Failed
Structural collapse: The acrylic portrait weighed ~350g. The cardboard frame (especially the horizontal top piece) couldn't support it. Finger joints split at stress points, and the frame buckled.
Root cause: Underestimated material weight. Acrylic density is ~1.2 g/cm³—a 12cm × 12cm × 3mm sheet is significantly heavier than anticipated. Cardboard corrugation direction and joint design weren't load-appropriate.
Pivot: Back-Support Stand
Salvaged components and redesigned on the fly:
- Two vertical supports (front)
- One horizontal base rail
- Two angled back braces (provides lean angle + stability)
- Kerf joints still used for assembly
Result: Stable enough for desktop display. Acrylic leans at ~70° angle, supported by back braces. No glue—friction fit only.
Vinyl Cutting: Coffee BAR Sticker
Side project to practice vinyl cutter operation.
- Design: "Coffee BAR" text in rounded sans-serif font
- Material: Red vinyl adhesive sheet
- Cutter: Roland CAMM-1 GS-24
- Process: Cut + weed (removed negative space)
Key Learnings
- Material properties matter: Acrylic is denser than it looks. Always calculate mass before designing support structures.
- Kerf compensation is critical: 0.2mm kerf offset worked well for 4mm cardboard. Joints were snug without forcing.
- Parametric design speeds iteration: Even though FreeCAD felt clunky, being able to adjust material thickness variable and regenerate all joints was valuable.
- Structural triangulation: The back-brace design worked because it created triangular load paths. Original cube frame had too many unsupported spans.
- Test before committing: Should have done a weight-bearing test with scrap cardboard before cutting final parts.
Next Steps (Future Iteration)
Now that I've learned Fusion 360 (Week 1 struggles with FreeCAD taught me to pivot tools), I plan to:
- Redesign the stand in Fusion with proper load analysis
- Use 3mm plywood instead of cardboard (laser cut or CNC routed)
- Add finger joint reinforcements or switch to mortise-and-tenon joints
- Incorporate adjustable angle brackets for portrait positioning
Reflection
This week taught me that fabrication isn't just about making parts fit—it's about understanding forces, material limits, and failure modes. The broken frame was frustrating but valuable: I learned more from the collapse than I would have from a successful first attempt. The pivot to a simpler design under time pressure mirrors real-world constraints, and salvaging the project with available materials felt more authentic than starting over.