Build a CNC Plasma Table Controller for Under $300

If you've got a plasma cutter and a CNC table frame, the only thing standing between you and automated cutting is the controller — and commercial options want $1,500–$3,000 for what amounts to a stepper driver, a relay, and some firmware.

We're building the whole thing for under $300. Open-source firmware, off-the-shelf modules, and a 3D-printed enclosure you can modify to fit your setup.

What We're Building

A complete CNC plasma controller that handles:

• 3-axis stepper control (X, Y, Z via GRBL)
• Torch Height Control (THC) — auto-adjusts Z based on arc voltage
• Arc-OK detection — won't move until the plasma is cutting
• Breakaway torch mount — magnetic mount that detaches on collision
• USB and SD card — run G-code from your computer or standalone

Parts List

Total: ~$280 vs. $1,800+ for a Hypertherm EDGE Connect or Langmuir controller.

Step 1: Understanding the Signal Flow

Before we wire anything, here's how the pieces talk to each other:

G-code (PC/SD)
    │
    ▼
ESP32 (FluidNC) ──── Step/Dir ────► DM542 Drivers ──► Stepper Motors
    │                                                       │
    ├── Arc-OK input ◄── THC Module ◄── Arc Voltage ◄──────┘
    │                         │
    ├── Z-axis adjust ◄───────┘ (THC raises/lowers torch)
    │
    └── Torch Fire relay ──► SSR ──► Plasma Trigger

The key insight: the THC module reads the arc voltage (which correlates to torch-to-work distance) and sends up/down signals to the ESP32's Z-axis. FluidNC handles this natively with the THC module enabled in config.

Step 2: Wiring the Stepper Drivers

Each DM542 driver needs:

1. Power input: 48V from the Meanwell PSU (V+ and GND)
2. Step/Dir signals: From the ESP32 GPIO pins (3.3V logic works, but use a level shifter if you get missed steps)
3. Motor wires: A+/A- and B+/B- to the NEMA23 (check your motor's datasheet for coil pairs)

DIP switch settings for the DM542:

• Current: set to 2.8A (matches our NEMA23)
• Microstep: 1600 pulses/rev (provides smooth motion without overwhelming the ESP32)

Step 3: Torch Height Control Wiring

The THC module sits between the plasma torch and the controller:

1. Arc voltage input — Connect to the plasma cutter's divided voltage output (most machines have a CPC port or raw arc voltage pins). The Proma THC-150 has a built-in voltage divider for 50–150V arc.
2. Up/Down outputs — These are open-collector signals that connect to the ESP32's THC input pins.
3. Arc-OK output — Goes HIGH when the plasma has established a stable arc. FluidNC uses this as a "motion enable" — the gantry won't move until arc is confirmed.

Step 4: FluidNC Configuration

Flash the ESP32 with FluidNC (grab the latest from fluidnc.com), then edit the YAML config:

name: "Plasma Table"
board: "ESP32"

stepping:
  engine: RMT
  idle_ms: 250
  dir_delay_us: 1
  pulse_us: 4

axes:
  x:
    steps_per_mm: 80
    max_rate_mm_per_min: 8000
    acceleration_mm_per_sec2: 500
    max_travel_mm: 1200
    motor0:
      step_pin: gpio.12
      direction_pin: gpio.14

  y:
    steps_per_mm: 80
    max_rate_mm_per_min: 8000
    acceleration_mm_per_sec2: 500
    max_travel_mm: 2400
    motor0:
      step_pin: gpio.26
      direction_pin: gpio.27

  z:
    steps_per_mm: 200
    max_rate_mm_per_min: 3000
    acceleration_mm_per_sec2: 200
    max_travel_mm: 75
    motor0:
      step_pin: gpio.15
      direction_pin: gpio.2

control:
  safety_door_pin: NO_PIN

coolant:
  flood_pin: gpio.25  # Torch fire relay

thc:
  arc_ok_pin: gpio.34
  up_pin: gpio.35
  down_pin: gpio.39
  delay_ms: 150       # Wait for arc to stabilize

Step 5: Enclosure

The 3D-printed enclosure mounts all components and keeps plasma EMI away from the electronics:

• Material: PETG (not PLA — operating near a plasma cutter means heat)
• Design: Split-shell with DIN rail mounts for the DM542 drivers
• Shielding: Line the inside with adhesive copper tape connected to earth ground

Download the STL files: enclosure-top.stl | enclosure-bottom.stl | din-clip.stl

Result

Total build time: about 6 hours across a weekend. The controller runs G-code from any CAM program that outputs standard G-code (Fusion 360, SheetCAM, Inkscape with G-code plugins).

You now have a plasma table controller that:

• Cost $280 instead of $1,800
• Runs open-source firmware you can modify
• Supports WiFi/web interface for wireless job loading
• Can be repaired with $12 replacement modules instead of proprietary boards