Chassis

The Lumen spectrometer chassis is designed for maximum mechanical stability while remaining manufacturable with standard tools (3D printer, CNC mill).

Materials

Component	Material	Process
Base plate	6061-T6 Aluminum	CNC milling
Uprights	304 Stainless Steel	Laser cutting
Optical mounts	PLA+ (matte black)	FDM 3D printing
Top cover	PMMA (plexiglass) 5 mm	Laser cutting
Screws & inserts	M3 Stainless Steel	Threaded + inserts

Dimensions

Length: 320 mm
Width:  240 mm
Height: 180 mm
Weight: 4.2 kg (assembled, without electronics)

The internal volume of 13.8 L accommodates the interferometer, IR source, sample compartment, and sensor.

Assembly

Step 1 — Base Plate

Attach the four anti-vibration feet (SBR rubber, Ø 30 mm) to the corners of the aluminum plate. Use M6 × 20 screws with lock washers.

Step 2 — Uprights

Screw the eight steel uprights onto the base plate. Check squareness with a precision square. Tolerance: ±0.5°.

Step 3 — Optical Breadboard

The optical breadboard (surfaced 6061 aluminum) mounts onto the uprights 80 mm above the base. It holds the Michelson interferometer. Use the drilling template provided in the design files.

Step 4 — Cover

The PMMA cover clips onto the uprights via M3 threaded inserts. Apply a silicone O-ring for dust sealing.

Mechanical Tolerances

Parameter	Tolerance
Base flatness	±0.05 mm
Optical parallelism	±0.02 mm
Laser alignment	±0.1 mrad
M3 screw clearance	0.1 – 0.15 mm

Thermal Stability

The chassis is designed to minimize differential thermal expansion:

• The aluminum base plate acts as a passive heatsink.
• PLA+ optical mounts feature expansion slots.
• The effective expansion coefficient is < 5 µm/m·K along the optical axis.

A thermal cycling test (15 °C → 35 °C, 10 cycles) showed an alignment drift of less than 0.05 mrad.

Manufacturing Files

All files are available in the GitHub repository:

hardware/
├── chassis/
│   ├── base_plate.dxf         # DXF for CNC milling
│   ├── base_plate.step        # 3D STEP model
│   ├── uprights.dxf           # Laser-cut uprights
│   ├── supports/              # STL files for 3D printing
│   │   ├── mirror_mount.stl
│   │   ├── beamsplitter_mount.stl
│   │   └── detector_mount.stl
│   └── cover.dxf              # PMMA cover
└── assembly.step              # Full assembly

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