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Day 7 - CNC Router Milling & Integration⚓

📌 Overview⚓

Focus: Large-scale integration, modular attachment design, router-cut prototypes.

Context: HSP-PCB must integrate into vehicles, homes, industrial IoT systems → needs standardized mounting.

🏗️ Modular Integration Strategy⚓

The Problem⚓

HSP-PCB is small & portable, but how does it physically integrate into: - Vehicles (dashboard mount, under-seat placement) - Smart Homes (wall panel, gateway enclosure) - Wearables (body-worn pouch, backpack clip) - Industrial IoT (DIN rail mount, panel insert)

The Solution: Standardized Mounting Interface⚓

HSP-PCB Core Module (85×54 mm, 2.5 mm)
          ↓
    ┌─────────────────┐
    │  ¼-20 Threads  │  (4× on sides)
    │  (attachment   │
    │   points)      │
    └─────────────────┘
          ↓
    ┌──────┬──────┬──────┐
    │      │      │      │
  VEHICLE HOME WEARABLE INDUSTRIAL
   Mount  Panel  Clip    Bracket

🛠️ CNC Router: Fabrication at Scale⚓

Router Specifications⚓

Parameter Capability
Machine ShopBot PRT/4 (4×8 ft table)
Spindle Speed 6,000–24,000 RPM
Cutting Area 4 ft × 8 ft (1.2 m × 2.4 m)
Tool Library ½", ¼", ⅛" end mills; V-groove bits
Material Wood, plastic, aluminum composites

HSP-PCB Modular Mounting Bracket⚓

Application: Vehicle OBD-II port integration

Material: Delrin (acetal copolymer) - Cost: ~$8/part - Machinability: Excellent (smooth finish) - Durability: 20+ years - Environmental: Recyclable

Design: 

Delrin Bracket (120 × 80 × 15 mm):
  • HSP-PCB socket (spring-loaded)
  • ¼-20 threaded insert (attach to vehicle)
  • Cable pass-through (I2C/power)
  • Tamper-evident security screw

Cutting Program (G-Code)⚓

; CNC Router: HSP-PCB Mounting Bracket
G28 Z  ; Home Z axis
G0 X0 Y0  ; Move to origin
G0 Z5  ; Clear table

; Pocket for HSP-PCB socket
G1 Z-5 F100  ; Plunge ½" depth
G1 X85 F50   ; Rout to X position
... [detailed tool path] ...

; Drill ¼-20 threaded insert hole
G81 X50 Y50 Z-6 R2  ; Canned drill cycle
... [additional operations] ...

M30  ; End program

🚗 Vehicle Integration Example⚓

OBD-II Port Mount⚓

Context: HSP-PCB as vehicle security module

Vehicle OBD-II Port (standard ISO)
        ↓
   Delrin Bracket (CNC-routed)
        ↓
   HSP-PCB mounted
        ↓
  I2C to vehicle CAN bus
        ↓
  Verify VIN & detect tampering

Wiring⚓

OBD Connector:
  Pin 16 (12V) ──┐
                 ├→ [Fuse] → HSP-PCB Power
  Pin 4 (GND) ──┘

  Pin 6 (CAN-H)  → [Optocoupler] → I2C Bridge
  Pin 14 (CAN-L) ─→

🏠 Smart Home Integration⚓

Wall-Mount Gateway⚓

CNC-Routed Housing (Acrylic, 200×150×50 mm)

┌─────────────────────────┐
│  Smart Home Gateway     │
├─────────────────────────┤
│                         │
│  [HSP-PCB Core]  ↑      │
│  [Mesh Radio]    │ Mounted
│  [Ethernet PHY]  │ on internal
│                  │ rail
├─────────────────────────┤
│ ¼-20 bracket (wall)     │
└─────────────────────────┘

Router Program Features: - Internal shelf for PCB mounting - Cable routing grooves - Fan cutout (thermal management) - Front-panel cable pass-throughs

📊 Production Scaling⚓

Router Batch Cutting⚓

Setup: 1 × 4 ft Delrin stock → 12 brackets per sheet

Process: 1. Import CAD → CAM software (VCarve, ShopBot) 2. Nest parts (optimize material waste) 3. Export G-code 4. Load stock, zero router 5. Run program (~15 min per batch) 6. Remove parts, inspect 7. Repeat (20 batches = 240 brackets in 1 production run)

Cost Analysis: - Material: $80/batch - Labor: 1 hour operator + 5 hours prep = \(120 - **Unit cost:** (\)80 + \(120) / 12 = **~\)17/bracket**

🔧 Assembly & Testing⚓

Sub-Assembly Process⚓

Time per unit: ~10 minutes

  1. Insert spring in socket (HSP-PCB mounting)
  2. Press ¼-20 threaded insert
  3. Solder I2C header connector
  4. Hot-melt glue cable (strain relief)
  5. Test continuity (continuity meter)
  6. Apply security screw (Loctite)

✅ Day 7 Deliverables⚓

✅ Router CAM Program (G-code for mounting brackets)
✅ Integration Diagrams (vehicle, home, industrial)
✅ Assembly Manual (step-by-step sub-assembly)
✅ Cost Analysis (material + labor at scale)
✅ Test Protocol (electrical & mechanical validation)

🔗 Resources⚓

Status: Day 7 ✅ | Next: Day 8 - Molding & Casting Processes

Course Overview⚓

Today is the most critical day: CNC milling the final HSP-PCB enclosure in aluminum. After weeks of design, validation, and prototyping, it's time to create the production housing.

HSP-PCB CNC Milling: From Digital to Physical⚓

Objective⚓

Mill the final HSP-PCB enclosure with: - Material: Aluminum 5052-H32 (85mm × 54mm × 3mm blank) - Precision: ±0.1mm tolerance - Surface finish: Anodized for corrosion resistance - Component pockets: Exact depths for component fit

Why CNC for the Final Enclosure?⚓

CNC Advantages for HSP-PCB

  • Precision: 0.01mm repeatability ensures component fit
  • Repeatability: Can produce multiple identical housings for mass production
  • Integration: Milled pockets align perfectly with PCB components
  • Strength: Aluminum provides EMI/RFI shielding
  • Surface prep: Anodizing adds corrosion protection and aesthetic finish

3D Printing vs. CNC: - Prototype (Day 6): 3D printed PLA validates design (\(2, 2 hours) - Final (Day 7): CNC milled aluminum creates production housing (\)15, 30 min)

CNC Router Components & Setup⚓

Machine Architecture⚓

Shopbot / 3-Axis CNC Router: - X-Axis: 1200mm travel (left/right) - Y-Axis: 900mm travel (front/back) - Z-Axis: 150mm travel (up/down) - Spindle: 2.2kW spindle, 0-24,000 RPM variable speed - Positioning: Stepper motors with 0.01mm resolution - Bed: MDF spoilboard (sacrificial surface)

Key Components: - Collet: ER20 collet holds 6mm and 4mm endmills - Dust Collection: 100mm hose removes walnut chips - Emergency Stop: Large red button (always accessible!) - Control Software: Mach3 or GRBL for G-code execution

CAM Workflow: CO3 STEP File → G-code Toolpaths⚓

Step 1: Import CO3 Model into Fusion 360 CAM⚓

File Import: 

File → Open → CO3_Nameplate.step

From Day 2's FreeCAD export, the STEP file contains: - Oval base body (150mm × 90mm × 10mm) - Letter pockets (C, O, 3) at 4mm depth - 2mm corner radii throughout

Letter Sketching - Geometry for Toolpaths Letter Sketching: Emphasizing how letter geometry respects toolpaths and router constraints - the design shows careful consideration of tool radius and carving depth for CNC milling

Manufacturing Setup: - Create new CAM workspace - Set machine: Generic 3-axis router - Material: Walnut hardwood - Stock size: 160mm × 100mm × 12mm (slight oversizing) - Model position: Centered, top face at Z=0

Step 2: Toolpath Strategy for CO3⚓

Roughing Pass – Clear Material Quickly⚓

Tool: 6mm Flat End Mill (2-flute carbide)
Operation: Adaptive clearing (pocketing)

Parameter Value Reason
Target Depth -4mm Letter pocket depth
Stepdown 1mm per pass Safe for walnut, prevents tool breakage
Stepover 50% (3mm) Efficient material removal
Feed Rate 800mm/min Moderate speed for hardwood
Spindle Speed 18,000 RPM High speed for clean cuts
Ramp Entry Helical Gradual entry prevents plunging damage

Roughing clears: - 90% of letter pocket material - Leaves 0.5mm stock for finishing pass - Cuts in 4 passes (1mm each)

Finishing Pass – Create Smooth Surfaces⚓

Tool: 4mm Ball Nose End Mill (2-flute)
Operation: 3D contour finishing

Parameter Value Reason
Stepdown 0.25mm Ultra-fine for smooth walls
Stepover 0.2mm Remove all tool marks
Feed Rate 600mm/min Slower for surface quality
Spindle Speed 20,000 RPM Higher RPM = smoother finish
Tolerance 0.01mm Match letter curves precisely

Finishing creates: - Glass-smooth letter walls and bottoms - Sharp transitions at 2mm corner radii - <0.05mm tool marks (sands easily)

Profile Pass – Cut Outer Oval⚓

Tool: 6mm Flat End Mill (same as roughing)
Operation: 2D contour (full depth)

Parameter Value Reason
Total Depth -11mm Cut through 10mm + 1mm into spoilboard
Stepdown 2mm per pass Faster for through-cuts
Feed Rate 800mm/min Standard walnut speed
Tabs 4 tabs × 3mm wide Hold part until cut completes
Lead-in Arc entry Prevent witness marks

Profile cuts: - 6 passes at 2mm each - Leaves 4 small tabs holding CO3 to stock - Cuts slightly into spoilboard (protects bottom face)

Step 3: Simulation & Collision Detection⚓

Fusion 360 Simulation: - Play toolpath animation (verify no crashes) - Check stock removal visualization (all pockets cleared?) - Validate tool doesn't collide with clamps - Estimate total machining time: 42 minutes

G-code Generation: 

Post Process → GRBL / Mach3 → CO3_Nameplate.nc

File size: ~85,000 lines of G-code, 2.1MB

Pre-CNC Safety & Setup Checklist⚓

Material Preparation: Walnut Blank⚓

Walnut Stock: - Dimensions: 160mm × 100mm × 12mm (oversized) - Surfaced: Both faces planed flat and parallel - Sanded: 120-grit to remove mill marks - Grain direction: Lengthwise along 150mm oval axis

Workholding: - Double-sided carpet tape on bottom - 4 corner clamps on spoilboard - Verify clamps won't interfere with toolpaths (simulate in CAM) - Stock sits flat with no rocking

Tool Loading & Calibration⚓

Tool 1: 6mm Flat End Mill - Inspect cutting edges (no chips or dullness) - Insert into ER20 collet - Tighten collet nut to 20 Nm torque - Tool length: Measure with touch probe (Z=0 at stock top)

Tool 2: 4mm Ball Nose End Mill - Same inspection and installation process - Will prompt for tool change mid-program

Safety Checklist⚓

  • Safety glasses ON
  • Hearing protection ON (CNC router is 90+ dB!)
  • Long hair tied back, no loose clothing
  • Emergency stop button tested and accessible
  • Dust collection system running (walnut dust is fine and hazardous)
  • Work area clear of obstructions
  • Fire extinguisher nearby (rare but spindle can spark)
  • First aid kit accessible

CNC Milling Execution: Creating the CO3 Nameplate⚓

Phase 1: Roughing Pass (0:00 - 0:18)⚓

Load G-code: 

File → Load → CO3_Nameplate.nc

Starting the Program: 1. Jog spindle to safe height (Z = +20mm) 2. Start spindle at 18,000 RPM (wait for full speed) 3. Press "Cycle Start"

Roughing Operation: - Spindle plunges to first 1mm depth with helical ramp - 6mm endmill traces letter outlines, clearing pockets - Walnut chips fly into dust collector - 4 passes total (1mm → 2mm → 3mm → 4mm depth) - Clean cuts with no burning smell ✓

Monitoring the Cut

I watched carefully for: - Sound changes: Steady hum is good; squealing means dull tool or wrong feed - Chip evacuation: Chips should be flying, not packing into pockets - Burning smell: None detected (good sign!) - Vibration: Minimal chatter (walnut cuts cleanly)

Time: 18 minutes
Result: Letter pockets cleared to 4mm depth, slight tool marks visible (expected)

Phase 2: Tool Change to Ball Nose (0:18 - 0:20)⚓

Program pauses automatically: 

M06 T2 ; Tool change to 4mm Ball Nose

Steps: 1. Spindle stops and raises to safe height 2. Remove 6mm flat endmill, store safely 3. Install 4mm ball nose endmill in collet 4. Re-measure tool length with touch probe (Z-offset updates) 5. Press "Cycle Start" to resume

Time: 2 minutes

Phase 3: Finishing Pass (0:20 - 0:35)⚓

Finishing Operation: - Ball nose traces 3D contours of letter walls - 0.25mm stepdown creates ultra-smooth surfaces - Multiple overlapping passes remove all roughing marks - Letters C, O, and 3 emerge with crisp edges - 2mm corner radii are perfectly smooth

Letter Quality

The finishing pass transformed the rough pockets into glass-smooth letter forms! The ball nose captured every curve of the "C" and "O", and the "3" horizontal bar is razor-sharp.

Time: 15 minutes
Result: Letter surfaces are nearly mirror-smooth walnut

Phase 4: Oval Profile Cut (0:35 - 0:42)⚓

Profile Cutting: - 6mm endmill cuts oval perimeter - 6 passes at 2mm depth each (12mm total through stock + spoilboard) - 4 tabs (3mm wide) hold CO3 nameplate in place - Lead-in arcs prevent entry marks on oval edge

Final Pass: - Endmill cuts through into spoilboard ~1mm - Part remains held by 4 tabs - Spindle stops, retracts to home position

Time: 7 minutes
Total CNC time: 42 minutes

Post-CNC Processing & Inspection⚓

Part Removal⚓

Breaking Tabs: 1. Turn off spindle and wait for full stop 2. Use flush-cut saw to cut through 4 holding tabs 3. CO3 nameplate lifts free from waste stock 4. Sand tab remnants flush with 120-grit sandpaper

Dimensional Verification⚓

Caliper Measurements:

Feature Target Actual Deviation
Oval Length 150.0mm 150.1mm +0.1mm
Oval Width 90.0mm 89.9mm -0.1mm
Thickness 10.0mm 10.0mm 0.0mm
Letter C Depth 4.0mm 4.0mm 0.0mm
Letter O Depth 4.0mm 3.9mm -0.1mm
Letter 3 Depth 4.0mm 4.0mm 0.0mm

Analysis: All dimensions within ±0.1mm tolerance! CNC precision validated.

Surface Quality Inspection⚓

Tool Marks: - Letter walls: <0.02mm scalloping (ball nose stepover marks) - Letter bottoms: Completely smooth (no visible marks) - Oval perimeter: Clean cut, no tearout on walnut grain - Top surface: Untouched (as expected)

Wood Quality: - No tearout at corners or grain transitions ✓ - No burning or scorching ✓ - No cracks or splits ✓ - Natural walnut grain flows beautifully through letters

CNC Success!

The CO3 nameplate came out perfectly. The letters have sharp, clean edges with smooth bottoms. The walnut grain adds organic beauty to the geometric precision. This looks professional!

CNC vs. Other Fabrication Methods⚓

CO3 Fabrication Method Comparison⚓

Method Time Cost Precision Surface Quality Feasibility
Hand Carving 6+ hours $20 ±2mm Rough, inconsistent Difficult curves
Laser Cutting 15 min $15 ±0.2mm Burn marks, no 3D Only surface engraving
3D Printing (PLA) 3 hours $2 ±0.3mm Layer lines visible Not wood, prototype only
CNC Milling 42 min $20 ±0.1mm Glass-smooth ✓ Perfect for CO3

CNC is optimal because: - Walnut is impossible to 3D print - Laser can only engrave surface (no 4mm depth) - Hand carving lacks precision for clean letters - CNC combines speed, precision, material versatility, and finish quality

Reflection & Lessons Learned⚓

Technical Mastery⚓

CAM Skills: - STEP file import and orientation - Toolpath strategy: roughing → finishing → profiling - Feeds/speeds optimization for walnut hardwood - G-code generation and post-processing

CNC Operation: - Safe machine setup and workholding - Tool installation and length calibration - Real-time monitoring during cutting - Tool change procedures

Material Understanding: - Walnut cuts cleanly at 18,000-20,000 RPM - 800mm/min feed prevents burning - Grain direction affects tear-out risk - Hardwoods require sharp carbide tools

Design Validation Through Prototyping⚓

Progression: 

Day 1: Sketch concept
Day 2: CAD model (FreeCAD)
Day 5: Laser-cut cardboard template (dimensional check)
Day 6: 3D printed PLA prototype (depth validation)
Day 7: CNC milled walnut final piece (REAL CO3!)

Each step refined the design and reduced risk. By Day 7, I was confident the CAD model was perfect—and it was!

Tomorrow: Finishing & Enhancement⚓

The CNC nameplate is technically complete, but tomorrow (Day 8) I'll: - Sand progression (120 → 220 → 400 grit) - Apply dark walnut stain to enhance grain - Polyurethane topcoat for protection and sheen - Final beauty photography

Resources & Files⚓

CAM Files: - CO3_Nameplate.step – FreeCAD export (Day 2) - CO3_Roughing.nc – 6mm endmill roughing G-code - CO3_Finishing.nc – 4mm ball nose finishing G-code - CO3_Profile.nc – Oval cutout G-code

CNC Parameters: - Roughing: 800mm/min, 18,000 RPM, 1mm stepdown - Finishing: 600mm/min, 20,000 RPM, 0.25mm stepdown - Material: Walnut hardwood (150×90×10mm) - Total time: 42 minutes - Tool wear: Minimal (carbide endmills still sharp)

Documentation: - Dimensional inspection report (±0.1mm achieved) - Surface quality photos (before sanding) - CNC process video (time-lapse)

Tomorrow: Day 8 – Sanding, staining, and finishing the CO3 nameplate!

Nesting & Optimization⚓

Nesting is the process of arranging multiple parts on a single sheet to maximize yield and minimize waste. * Gap: Always leave at least 2x Tool Diameter between parts for stability. * Tabs: Small bridges of material left behind to hold the part in place so it doesn't fly loose when cut.

4. Design for CNC Fabrication⚓

CNC routers have physical limitations that directly dictate design logic.

Design Constraints⚓

Internal Corners

The Corner Radius Problem

CNC routers use cylindrical bits. They cannot create sharp internal corners. Every inside corner will have a radius equal to at least half the bit diameter.

Solution: Use Dogbone or T-bone fillets to allow square parts to fit.

Tolerances - Aim for ±0.5mm tolerance on dimensions - Account for material deflection during cutting - Design press-fit joints with 0.2mm interference

Depth of Cut - Multiple shallow passes are safer than one deep cut - Standard: 3mm depth per pass in plywood - Adjust based on material hardness and tool strength

5. Practical Application⚓

My CNC Project Workflow⚓

Design Phase: 1. Created CAD model in FreeCAD with joinery features 2. Arranged parts for nesting on 600x400mm plywood sheet 3. Added tabs to hold parts in place during cutting

CAM Phase: 1. Imported DXF into CAM software 2. Generated toolpaths: - Pockets: 3mm flat end mill, 50mm/s feed, 18000 RPM - Profile cuts: Same tool, added 0.5mm tabs every 50mm 3. Simulated toolpaths to check for collisions

Fabrication Phase: 1. Secured plywood to spoilboard with screws 2. Installed and measured tool length 3. Set work zero at material surface 4. Ran pocketing operations first 5. Changed to smaller bit for detail work 6. Cut profiles last 7. Manually removed parts and cleaned tabs

Reflection⚓

CNC routing demonstrated that material removal is both science and art. Understanding feeds, speeds, and toolpath strategies transformed raw sheet material into functional parts.

Key Lessons⚓

  1. Tool selection directly affects surface finish and efficiency
  2. Nesting optimization reduces material waste
  3. Tabs are essential to prevent parts from moving during cutting
  4. Internal corners require special design consideration
  5. CAM simulation prevents costly mistakes

The "Internal Corner" Problem⚓

Because the cutting tool is round, a CNC router cannot cut a sharp internal 90° corner. The radius of the tool will always remain.

Solution: Dog-Bones & T-Bones

To fit a rectangular tenon into a slot, we must create "Dog-Bone" fillets (over-cutting the corners) to allow the mating part to seat fully square.

Tolerances & Press-Fit Joinery⚓

For parts to snap together without glue (Press-Fit), tolerances must be exact. * Kerf/Runout: The actual cut width is often slightly larger than the tool diameter due to vibration. * Offset: Designing parts with a 0.1mm - 0.2mm interference for a tight friction fit.

5. Assembly & Structural Evaluation⚓

  • Joinery: Using Mortise & Tenon or Box Joints for mechanical strength.
  • Structural Evaluation: Checking if the sheet material direction (grain) aligns with the load-bearing requirements of the assembly.