CNC Mill: Complete Documentation
Overview and Theory
CNC Mill: Complete Documentation
Overview & Theory
What is a CNC Mill?
CNC = Computer Numerical Control
A CNC mill uses computer-controlled motors to move a cutting tool (router bit) in precise patterns, cutting material based on digital designs.
For our project: Cut plywood panels for the proa hull.
Design Philosophy: Cheap, Sturdy, Capable
Requirements:
- Cutting area: 4’ x 8’ (full plywood sheet)
- Material capability:
- 2” foam board (multiple passes) ✓
- 3/4” Baltic birch plywood (BONUS goal)
- Budget: <$2,500 total
- Build time: 40-60 hours
- Skill level: Intermediate DIY (can use drill, saw, wrench)
Theory of Operation:
3-Axis Movement:
- X-axis: Left/right (8’ travel for our build)
- Y-axis: Front/back (4’ travel)
- Z-axis: Up/down (6” travel - enough for material + clearance)
How it cuts:
- Computer sends coordinates to controller
- Controller drives stepper motors
- Motors move gantry/spindle to exact position
- Spindle rotates cutting bit at high speed
- Bit removes material layer by layer
Multiple passes for thick material:
- 3/4” plywood: Cut in 3-4 passes @ 0.2-0.25” depth each
- 2” foam: Cut in 8-10 passes @ 0.2-0.25” depth each
- Prevents bit breakage, reduces motor load
Recommended Design: “Lowrider CNC v3”
Why this design:
- Proven in community (1000+ builds)
- Uses EMT conduit (cheap: $20 for 10’)
- Fits 4’x8’ sheets
- Strong enough for plywood
- Detailed instructions available
- Active forum support
Source: V1 Engineering (v1e.com/lowrider-cnc)
Key innovation: Rails run UNDER the table (lowrider), saving vertical space.
Complete Parts List
Frame & Motion (Structural)
| Part | Specification | Quantity | Cost (USD) | Source |
|---|---|---|---|---|
| EMT Conduit 3/4” | 10’ lengths | 5 pieces | $100 | Home Depot |
| Plywood 3/4” | 4’x8’ sheet (spoilboard) | 2 sheets | $100 | Home Depot |
| 2x4 Lumber | 8’ lengths (table frame) | 8 pieces | $40 | Home Depot |
| MDF 3/4” | 2’x4’ (gantry plates) | 1 sheet | $20 | Home Depot |
Frame Subtotal: $260
Motion Components
| Part | Specification | Quantity | Cost | Source |
|---|---|---|---|---|
| Stepper Motors NEMA 23 | 3.0 Nm, 1.8° step | 4 motors | $120 | StepperOnline |
| Linear Bearings LM8UU | 8mm ID | 20 pieces | $30 | Amazon |
| 8mm Linear Rods | 400mm length | 8 rods | $40 | Amazon |
| GT2 Timing Belt | 6mm wide, 2mm pitch | 20 meters | $25 | Amazon |
| GT2 Pulleys | 20-tooth, 8mm bore | 4 pulleys | $20 | Amazon |
| Lead Screw 8mm | T8 (2mm pitch), 500mm | 1 screw | $15 | Amazon |
| Lead Screw Nut | T8 anti-backlash | 1 nut | $8 | Amazon |
Motion Subtotal: $258
Electronics
| Part | Specification | Quantity | Cost | Source |
|---|---|---|---|---|
| Controller Board | GRBL-based (Arduino CNC Shield) | 1 board | $25 | Amazon |
| Motor Drivers | A4988 or DRV8825 | 4 drivers | $20 | Amazon |
| Power Supply | 24V 15A (360W) | 1 unit | $40 | Amazon |
| Emergency Stop | Red mushroom button | 1 button | $10 | Amazon |
| Limit Switches | Mechanical endstops | 6 switches | $15 | Amazon |
| Wiring Kit | 18AWG, connectors | 1 kit | $25 | Amazon |
Electronics Subtotal: $135
Spindle (Router)
| Part | Specification | Quantity | Cost | Source |
|---|---|---|---|---|
| Router | Makita RT0701C (1.25 HP) | 1 router | $120 | Amazon |
| Router Mounting Bracket | 3D printed or aluminum | 1 bracket | $15 | Print/Buy |
| Dust Shoe | 3D printed | 1 shoe | $10 | |
| Router Bits | 1/4” upcut spiral (plywood) | 3 bits | $30 | Amazon |
| Router Bits | 1/4” ballnose (foam) | 2 bits | $20 | Amazon |
Spindle Subtotal: $195
Fasteners & Hardware
| Part | Specification | Quantity | Cost | Source |
|---|---|---|---|---|
| M5 Bolts | Assorted lengths | 100 pack | $15 | Amazon |
| M5 Nuts | Lock nuts | 100 pack | $10 | Amazon |
| Wood Screws | 2.5”, 3” deck screws | 1 lb box | $15 | Home Depot |
| T-Track | Aluminum, 4’ lengths | 2 pieces | $30 | Amazon |
| Hold-Down Clamps | CNC work holding | 4 clamps | $25 | Amazon |
Hardware Subtotal: $95
TOTAL COST BREAKDOWN
| Category | Cost |
|---|---|
| Frame & Motion | $260 |
| Motion Components | $258 |
| Electronics | $135 |
| Spindle | $195 |
| Fasteners & Hardware | $95 |
| SUBTOTAL | $943 |
| Contingency (15%) | $142 |
| GRAND TOTAL | $1,085 |
Under budget by $1,415!
Alternative: If You Have On-Hand Items
Substitutions (Cost Reductions)
If you have:
Router already?
- Savings: $120
- Most trim routers work (1-1.5 HP minimum)
Old computer power supply?
- Savings: $40
- Needs 12V or 24V rail with 10A+ capacity
Scrap plywood/MDF?
- Savings: $120
- Can use for spoilboard and gantry plates
3D Printer access?
- Savings: $50-100
- Print motor mounts, belt tensioners, dust shoe
Electronics experience?
- Build your own controller: Arduino Uno + CNC Shield
- Savings: $0 (same cost, but more control)
Potential Total with Substitutions: $650-800
Build-Out Instructions
Phase 1: Table Frame (8 hours)
Materials:
- 8x 2x4s (8’ lengths)
- 2x 3/4” plywood sheets
- Wood screws, wood glue
Steps:
- Cut 2x4s to create 4’x8’ rectangular frame
- Add cross supports every 16” (prevents sagging)
- Attach first plywood sheet (structural base)
- Level frame (critical for accuracy)
- Attach second plywood sheet (sacrificial spoilboard)
Result: Rigid, flat table ready for rails.
Phase 2: Rail Installation (4 hours)
Materials:
- 5x EMT conduit 3/4” (cut to length)
- Linear bearings LM8UU
- MDF mounting blocks
Steps:
- Cut EMT: 2x 8’ lengths (X-axis), 2x 4’ lengths (Y-axis), 1x 18” (Z-axis)
- Create bearing blocks from MDF
- Mount X-rails parallel on table (exactly 24” apart)
- Slide bearing blocks onto rails
- Attach gantry structure to bearing blocks
Result: Smooth-rolling gantry.
Phase 3: Motors & Belts (6 hours)
Materials:
- 4x NEMA 23 stepper motors
- GT2 timing belt & pulleys
- Motor mounting brackets
Steps:
- Mount motors to gantry structure
- Install pulleys on motor shafts
- Route belts around pulleys and gantry
- Tension belts (should “twang” when plucked)
- Test manual movement (should roll smoothly)
Result: Motorized axes ready for wiring.
Phase 4: Electronics (8 hours)
Materials:
- Controller board, motor drivers
- Power supply, wiring
- Emergency stop, limit switches
Steps:
- Mount controller in enclosure box
- Install motor drivers on controller
- Wire motors to drivers (check polarity!)
- Wire power supply to controller
- Install limit switches at travel ends
- Wire emergency stop (safety critical!)
- Connect to computer via USB
Result: Powered, controllable CNC.
Phase 5: Z-Axis & Spindle (6 hours)
Materials:
- Lead screw & nut
- Router & mounting bracket
- Z-axis carriage
Steps:
- Assemble Z-axis carriage
- Mount lead screw vertically
- Attach stepper motor to lead screw
- Mount router in bracket
- Attach bracket to Z-carriage
- Test Z-movement (should lift router smoothly)
Result: 3-axis motion complete.
Phase 6: Calibration & Testing (8 hours)
Software:
- Install Universal G-Code Sender (free)
- Flash GRBL firmware to Arduino
Steps:
- Home all axes using limit switches
- Measure actual travel distances
- Calibrate steps/mm in GRBL settings
- Cut test square (100mm x 100mm)
- Measure cut square (should be exactly 100mm)
- Adjust calibration if needed
- Test foam cutting (shallow passes first)
- Test plywood cutting (SLOW feed rate initially)
Result: Accurate, functional CNC ready for production.
Safety Checklist
Before EVERY use:
- Emergency stop tested and functional
- Router bit secure and undamaged
- Material clamped firmly to spoilboard
- Clear work area (no loose objects)
- Eye protection on
- Ear protection on (routers are LOUD)
- Dust collection connected (plywood dust is hazardous)
- G-code preview checked (no obvious errors)
- Feeds & speeds appropriate for material
Never:
- Run CNC unattended
- Reach into cutting area while spindle running
- Override safety interlocks
- Cut unknown materials (could be toxic when vaporized)
User Guide: Cutting Proa Panels
Workflow:
- Design: Create panel DXF in CAD software
- CAM: Generate toolpaths in Fusion 360 CAM or EstlCAM
- Export: Save G-code file to SD card or USB
- Setup: Clamp plywood to spoilboard, zero router bit
- Cut: Send G-code, monitor first pass closely
- Finish: Remove tabs, sand edges
Settings for 3/4” Plywood:
- Bit: 1/4” upcut spiral
- RPM: 18,000 (Makita setting 3)
- Feed rate: 40 in/min
- Plunge rate: 15 in/min
- Depth per pass: 0.20”
- Total passes: 4 (for 3/4” material)
Settings for 2” Foam:
- Bit: 1/4” ballnose
- RPM: 12,000 (Makita setting 2)
- Feed rate: 80 in/min
- Plunge rate: 30 in/min
- Depth per pass: 0.25”
- Total passes: 8 (for 2” material)
What You’ll Be Able to Cut:
Proa Main Hull:
- 8 plywood panels @ 6mm thick
- Total cutting time: ~6 hours (including setup)
Proa Ama:
- 6 plywood panels @ 6mm thick
- Total cutting time: ~4 hours
Bulkheads:
- 6 pieces from 12mm plywood
- Total cutting time: ~2 hours
Total project cutting: ~12 hours (way faster than jigsaw by hand!)
Resources & Community:
Forums:
- V1 Engineering Forum (lowrider CNC specific)
- CNC Zone (general CNC discussion)
- r/hobbycnc (Reddit community)
Software (Free):
- GRBL (controller firmware)
- Universal G-Code Sender (control software)
- EstlCAM (CAM - generates toolpaths)
- Inkscape (2D design)
YouTube Channels:
- V1 Engineering (builder of Lowrider design)
- Winston Moy (CNC beginner tutorials)
- NYC CNC (professional techniques)
BUILD TIME: 40 hours
COST: $1,085
CAPABILITY: Everything you need for the proa project