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Week 4 of 12 · Foundations

3D Printing & Laser Fabrication

Turn your Week 3 CAD model into physical hardware: slicer toolpaths, DFAM orientation, heat-set threaded insert installation, and laser kerf compensation.

~5 hrs Workshop & Lab FDM + Laser

Concept Additive vs. Subtractive Physics

In software, code either runs or throws an exception. In physical manufacturing, parts fail subtly due to the laws of thermodynamics and material mechanics. This week bridges the screen to the bench.

FDM 3D Printing (Additive): Plastic filament is heated to liquid glass transition and deposited in horizontal X-Y tracks. The resulting part is anisotropic: strong in tension along the extrusion lines, but prone to splitting along the Z-axis layer boundaries under shear loads. Increasing the number of perimeters (outer walls) from 2 to 4 increases part torsional strength by over 200%—far more effectively than simply bumping infill percentage.

Laser Cutting (Subtractive): A focused laser beam vaporizes material along a 2D vector path. The beam has physical thickness (kerf ≈ 0.15–0.25mm). If you cut two interlocking slots without kerf offset, the joint will be loose and rattle.

Kit What you need this week

  • FDM 3D printer (Bambu Lab, Prusa, or Ender)
  • Filament: PETG (recommended for motor plates) or PLA
  • Soldering iron with conical or dedicated heat-set insert tip
  • M3 × 4.5mm brass heat-set threaded inserts (Qty 4)
  • M3 × 8mm socket-head cap screws & 2.5mm hex key
  • Laser cutter (e.g. xTool F2 Ultra) + 3mm sheet ply or acrylic
  • Digital calipers

Build Step by step

Step 1

Slicing for mechanical strength (not cosmetics)

Open your Week 3 STL in your slicer (PrusaSlicer, Bambu Studio, or Cura). Configure mechanical settings:

  • Layer Height: 0.20 mm (optimal layer bond strength).
  • Wall Loops / Perimeters: Set to 4 walls (1.6mm solid shell). This guarantees the M3 insert bosses are 100% solid plastic, preventing delamination when screws are torqued down.
  • Infill: 25% Gyroid (Gyroid distributes shear stress equally in all 3 axes without weak directional planes).
  • Print Orientation: Lay the flat bottom plate directly on the print bed so all screw holes and standoffs point vertically (Z-axis).
Step 2

Print the bracket

Clean the build plate with 99% Isopropyl Alcohol (IPA). Watch the first layer go down—the lines should be slightly squished and completely bonded without gaps or peeling corners.

Step 3

Install M3 heat-set threaded inserts

Once the print cools, install the brass inserts into the standoff pilot holes:

  • Set soldering iron temperature to 230°C (for PLA) or 250°C (for PETG).
  • Place the brass insert upright over the 3.2mm printed pilot hole.
  • Gently rest the iron tip inside the insert. As the brass conducts heat into the plastic, apply light downward pressure.
  • When the insert is 95% flush, remove the iron and immediately press a flat cold metal block (or the side of your caliper jaw) against the top of the insert to set it perfectly flush with the plastic face.
Step 4

Laser cut the chassis base panel

Open laser files/laser_base.dxf (or your custom base vector). Set up the xTool F2 Ultra:

  • Run a small 20mm × 20mm test square on scrap 3mm material to verify clean penetration.
  • Enable kerf compensation in LightBurn (offset +0.10 mm outward for perimeter cuts, -0.10 mm inward for holes).
  • Execute the full base panel cut.
Step 5

Fit-check & bolt assembly

Perform the physical fit check:

  • Drop the real NEMA-17 motor onto the bracket. Does the 22mm center boss seat cleanly into the registration pocket?
  • Thread four M3×8mm bolts through the slotted channels into the motor face. Do the bolts slide smoothly through the 6mm travel range?
  • Bolt the VMA327 limit switch onto the heat-set standoff bosses. Torque down the M3 screws firmly—verify that the brass inserts hold solid without pulling out.
1. Position Insert 2. Heat with Iron (230°C) 3. Flush Quench with Metal Solid Permanent Thread
Figure 4.1: The 3-stage heat-set insert thermal installation procedure.
Make it yours
  • Try destructive testing on a test coupon: heat-set an insert into a printed test block and see how much torque it takes to strip the brass threads vs pulling the insert out.
  • Engrave alignment tick marks (1mm increments) onto the laser-cut base plate alongside the motor slots to read motor travel visually.

If it breaks Troubleshooting

Insert goes in crooked / tiltedReheat the insert gently with the iron tip and immediately press a flat steel plate flush against the top while the plastic solidifies.
Motor plate warped / bentStepper motors get warm (50°C+). If printed in PLA, motor heat can cause thermal creep over time. Reprint the bracket in PETG for long-term dimensional stability.
Laser cut leaves burnt / charred edgesIncrease cutting speed or use air-assist. For acrylic, remove protective paper film before cutting to prevent flare-ups.
This week's checkpointYou hold a physical printed NEMA-17 stepper bracket with flush M3 heat-set inserts installed, and a clean laser-cut base panel. Both fit-check against the real hardware without forcing.
Next week: Stepper motors — wiring the motor coils, driving microsteps, and coding an automated switch-homing routine.
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