2020 Aluminum Extrusion Skeleton Blueprint & Structural Specifications

System: 6U 19-Inch Open-Source Tri-Mode Storage Array
Document ID: MECH-SPEC-01
Compliance Standard: EIA-310-D / IEC 60297-3-100 (19-Inch Rack Cabinets)
Frame Material: 6063-T5 Anodized Aluminum 2020 T-Slot Extrusion (6mm Slot, Series 20)

1. Dimensional Envelope & EIA-310-D Compliance

The 6U chassis is engineered to maximize internal compute and storage density while guaranteeing seamless insertion into standard 19-inch 4-post or 2-post server racks without binding.

       ◄────────────────────────── 482.6 mm [19.00"] Front Flange ────────────────────────►
       ◄─── 23.3 mm ───►◄────────────── 436.0 mm [17.17"] Chassis Width ──────────────►◄─── 23.3 mm ───►
      ┌────────────────┬──────────────────────────────────────────────────────────────┬────────────────┐
  ▲   │  [O] 6U Ear    │  [ Modular 3D-Printed Facade with Interlocking Dovetails ]   │   6U Ear [O]   │
  │   │                ├──────────────────────────────────────────────────────────────┤                │
  │   │  [O]           │  8x Toolless Vertical U.3 (NVMe/SAS/SATA) Hot-Swap Bays      │          [O]   │
260.0 │                │  (Pitch: 49.5 mm, Channel Width: 23.4 mm)                    │                │
 mm   │  [O]           │                                                              │          [O]   │
[10.24│                ├──────────────────────────────────────────────────────────────┤                │
 in]  │  [O]           │  Front Air Intake Mesh (50% Open Aerodynamic Hexagonal Grid) │          [O]   │
  ▼   └────────────────┴──────────────────────────────────────────────────────────────┴────────────────┘
                       ◄───────────────────── 500.0 mm [19.69"] Depth ────────────────►

Critical Envelope Dimensions:

Total Height (Skeleton + Sheets): 260.0\,\text{mm} + 2 \times 1.2\,\text{mm (Skin)} = \mathbf{262.4\,\text{mm}} (EIA-310-D 6U max: 266.70\,\text{mm}, giving 4.3\,\text{mm} safety clearance).
Total Width (Skeleton Body): \mathbf{436.0\,\text{mm}} (EIA-310-D rack post clearance min: 450.85\,\text{mm}, giving 14.85\,\text{mm} total side clearance).
Total Depth: \mathbf{500.0\,\text{mm}} (Chassis front lip to rear exhaust plane).
Front Faceplate Width: \mathbf{482.6\,\text{mm}} (19.00 inches).
Rack Ear Mounting Hole Centers: \mathbf{465.1\,\text{mm}} horizontal pitch; EIA standard alternating vertical hole spacing (15.875\,\text{mm} - 15.875\,\text{mm} - 12.700\,\text{mm} per 1U).

2. Structural Extrusion Cut-List

All frame members are cut from standard 20mm x 20mm T-slot (or V-slot) aluminum extrusions. Precision cutting tolerance: \pm 0.2\,\text{mm}, square cut ends < 0.1^\circ.

Part ID	Description / Position	Quantity	Cut Length (mm)	Total Linear (mm)	Sourcing / Stock Item (80/20 / Faztek / Misumi)
EXT-01	Vertical Corner Uprights (Z-axis)	4	260.0 mm	1,040.0 mm	20-2020 / HFS5-2020-260
EXT-02	Width Crossbars (X-axis, Top/Bottom Front/Rear)	4	396.0 mm	1,584.0 mm	20-2020 / HFS5-2020-396
EXT-03	Depth Side Rails (Y-axis, Top/Bottom Left/Right)	4	460.0 mm	1,840.0 mm	20-2020 / HFS5-2020-460
EXT-04	Mid Fan-Wall Vertical Stretchers (Z-axis)	2	220.0 mm	440.0 mm	20-2020 / HFS5-2020-220
EXT-05	Mid Fan-Wall & Drive Backplane Rails (X-axis)	2	396.0 mm	792.0 mm	20-2020 / HFS5-2020-396
EXT-06	Rear Mezzanine Floor Braces (Y-axis)	2	300.0 mm	600.0 mm	20-2020 / HFS5-2020-300
TOTAL	Linear 2020 Extrusion Requirement	18 pcs	—	6,296.0 mm	~6.3 Meters (~3x 2.5m or 7x 1m standard bars)

3. Structural Joinery & Fastener Schedule

To prevent vibration loosening under 24/7 server fan operation and mechanical hard drive harmonic vibration, all connections utilize hardened steel fasteners and cast zinc/aluminum corner gussets.

                    CORNER GUSSET ASSEMBLY EXPLOSION
                     
                     [EXT-01 Vertical Upright]
                            │
                     ┌──────┴──────┐
                     │    ( | )    │ ◄── 2020 Corner Gusset (Cast Zinc)
                     │ ┌─────────┐ │
       [M5x10mm BHSCS]─┼─┤ (O) (O) ├─┼─► [M5 Drop-In T-Nut (Spring Loaded)]
                       │ └─────────┘ │
                     └──────┬──────┘
                            │
                     [EXT-02 Crossbar / EXT-03 Side Rail]

Fastener Schedule Matrix:

Fastener Item	Specification	Quantity	Application	Est. Cost (1k Vol)
FAST-01	M5 x 10mm Button Head Socket Cap Screws (ISO 7380, Class 10.9)	48 pcs	Corner gussets to 2020 extrusion	$2.40
FAST-02	M5 Roll-in T-Nuts with Spring Ball (6mm slot)	48 pcs	Corner gusset anchor channels	$3.60
FAST-03	2020 90-Degree Cast Aluminum Corner Gusset Brackets (20x20mm)	24 pcs	8 primary frame corners + 4 internal joints	$4.80
FAST-04	M4 x 8mm Button Head Screws + M4 Drop-in T-Nuts	32 pcs	Securing laser-cut sheet metal panels	$2.20
FAST-05	M3 Heat-Set Brass Threaded Inserts (Ø4.2mm OD, 4.0mm L)	40 pcs	Pressed into 3D-printed facade and fan wall	$1.80
FAST-06	M4 Heat-Set Brass Threaded Inserts (Ø5.6mm OD, 5.0mm L)	16 pcs	Facade-to-extrusion mounting interfaces	$1.20
TOTAL	Hardware Fasteners Package	—	Complete structural fastening kit	~$16.00

4. Mechanical Subsystem Spatial Zones

TOP VIEW SKELETON LAYOUT (Z=0 Plane)
┌─────────────────────────────────────────────────────────────────────────────┐
│ ◄───────────────────────── 436.0 mm Skeleton Width ───────────────────────► │
│                                                                             │
│ ┌───────────┐ ◄────────── 396.0 mm Front Crossbar (EXT-02) ───────► ┌───────────┐
│ │ EXT-01(L) │                                                       │ EXT-01(R) │
│ └─────┬─────┘                                                       └─────┬─────┘
│       │                                                                   │
│   ▲   │  [ZONE 1: STORAGE ARRAY - 0 to 125 mm Depth]                      │
│   │   │  - 8x Vertical U.3 Toolless Caddies (Width 49.5mm pitch)          │
│ 125mm │  - SFF-TA-1001 Passive Backplane PCB (Mounted at Y=115mm)         │
│   │   │                                                                   │
│   ▼   ├───────────────────────────────────────────────────────────────────┤
│       │  [ZONE 2: PRESSURE WALL & FAN BARRIER - 125 to 195 mm Depth]      │
│   ▲   │  - Mid Crossbar (EXT-05) + Vertical Stretchers (EXT-04)           │
│  70mm │  - 3x 120mm Enterprise PWM Fans (Noctua/Sanyo/Delta)              │
│   │   │  - 3D-Printed Acoustic Shroud with 5mm Filleted Baffles           │
│   ▼   ├───────────────────────────────────────────────────────────────────┤
│       │  [ZONE 3: COMPUTE & GPU MEZZANINE - 195 to 500 mm Depth]          │
│   ▲   │  - Radxa CM3 + Broadcom SAS3408 Carrier Baseboard (Y=205 to 330mm)│
│       │  - Unobstructed Mezzanine Space (300mm length)                    │
│ 305mm │  - Vertical GPU Compute Bay with Rear Exhaust Venting             │
│   │   │  - External 12V High-Current Input Panel                          │
│   ▼   │                                                                   │
│ ┌─────┴─────┐ ◄────────── 396.0 mm Rear Crossbar (EXT-02) ────────► ┌─────┴─────┐
│ │ EXT-01(RL)│                                                       │ EXT-01(RR)│
│ └───────────┘                                                       └───────────┘
└─────────────────────────────────────────────────────────────────────────────┘

5. Structural Squaring & Assembly Protocol

Sub-Assembly 1 (Left & Right Side Ladders):
- Lay two EXT-01 vertical uprights (260mm) parallel on a flat reference table.
- Join using two EXT-03 side rails (460mm) at the top and bottom with 4x corner gussets (FAST-03).
- Use a precision machinist's square (90^\circ \pm 0.05^\circ) across diagonal corners (L_{\text{diag}} = \sqrt{260^2 + 460^2} = 528.4\,\text{mm}). Torque M5 screws to 4.5\,\text{N}\cdot\text{m}.
- Repeat for the opposite side ladder.
Sub-Assembly 2 (3D Box Integration):
- Stand both side ladders vertically.
- Bridge the ladders using the four EXT-02 width crossbars (396mm) at the front-top, front-bottom, rear-top, and rear-bottom.
- Measure 3D spatial diagonals (L_{\text{3D}} = \sqrt{260^2 + 460^2 + 396^2} = 660.3\,\text{mm}). Verify that all four 3D diagonals match within \pm 0.5\,\text{mm}.
Sub-Assembly 3 (Mid Fan Wall & Mezzanine Rails):
- Drop 4x M5 roll-in T-nuts into the top and bottom inner slots of EXT-03 at position Y = 135\,\text{mm}.
- Bolt in the lower and upper EXT-05 mid-crossbars (396mm) and EXT-04 vertical stretchers (220mm).
- Bolt the two EXT-06 mezzanine rails (300mm) to the bottom rear frame.

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