Reviving an Orphaned CNC Plasma Table After Controller Loss

Overview

When a CNC plasma table loses its control computer—either through theft, hardware failure, or vendor obsolescence—the machine itself remains functionally intact. Servo drives, motors, proximity sensors, and the plasma source typically survive the event. The path to operational status involves three phases: drive and signal identification, controller selection and installation, and plasma-specific tuning. This guide walks through each phase using field-observable data you can collect with basic tools—no original manufacturer documentation required.

CR Electronic, an Italian OEM, is now defunct, which eliminates any possibility of retrieving proprietary firmware or configuration files. The repair methodology below applies broadly to orphaned plasma tables from any defunct or unresponsive vendor.

Phase 1 — Cabinet Inspection and Drive Assessment

Before connecting any new controller, identify what drives and motors the cabinet contains. Power down the enclosure, open all access panels, and photograph every label.

Identifying Drive Type

Servo drives and stepper drives have distinct visual signatures:

• Servo drives: Metallic enclosure with prominent heat sink on rear or side; diagnostics LED display or 7-segment readout; separate encoder feedback connector (typically 9-pin or 15-pin D-sub); DC bus capacitors visible internally.
• Stepper drives: Smaller plastic or sheet-metal housing; often fan-cooled; typically two screw-terminal blocks for motor windings; no encoder connector.

Record every label: vendor name, model number, input voltage, and rated current per axis. These specs dictate whether the existing drives can be reused directly with a new motion controller.

Critical Signals to Identify

Locate the terminal strip or connector where the original controller interfaced with the drives. Map each signal wire by color and function. Key signals for any plasma table motion system:

Phase 2 — Selecting a Replacement Controller

Three viable controller categories exist for plasma table retrofit:

Mach3 / Mach4 (Parallel Port or Ethernet)

Mach3 remains the most common DIY and small-shop plasma controller. It runs on standard Windows PCs and supports plasma-specific features including THC input, arc-ok sensing, and adaptive pierce height. Mach3 outputs pulse trains via the parallel port or optional motion boards. If the existing drives accept step/direction pulses rather than ±10V analog, a standard parallel port is sufficient. For ±10V drives, use a separate analog output card such as the CNC4PC C11G or PMDX-122.

Mach4 is the newer iteration with a more modular architecture, though the plasma plugin ecosystem is less mature than Mach3.

LinuxCNC (PCI Parallel Port or Ethernet)

LinuxCNC is free and runs on standard PC hardware. It natively supports parallel port pulse generation and, with appropriate hardware, ±10V analog output. For Ethernet-based control, the Mesa Ethernet-FPGA combinations (e.g., 7I76E) pair with LinuxCNC to deliver high-count step/direction or encoder feedback channels over a single CAT5 cable.

Pokeys57CNC and EtherCNC Controllers

Ethernet-based controllers like the Pokeys57CNC and USS-PMC offer modern connectivity (no legacy parallel port required), built-in plasma torch relay drivers, Arc Voltage ADC inputs for THC, and firmware-configured pin assignments. These are increasingly common in new builds and retrofit work because they eliminate the aging PC dependency.

Phase 3 — Signal Wiring and I/O Mapping

Match the new controller's outputs to the existing drive inputs. The following assumes a ±10V analog servo architecture:

1. Connect GND between controller analog ground and drive signal common. Floating grounds cause drift and erratic motion.
2. Wire axis commands: Controller DAC channel 0 → X axis command input, Ch1 → Y, Ch2 → Z. Typical input impedance of servo drives is 10–100 kΩ, so signal integrity is robust over short runs.
3. Wire enable signals: Controller enable output (24 V) → each drive's enable terminal. Some drives accept a PWM enable signal—verify from the drive manual.
4. Wire home switches: Each axis proximity sensor output → dedicated controller input. CR Electronic systems typically used NPN sensors; pull-up resistors may be needed if the new controller uses sourcing inputs.
5. Wire torch start: Controller relay output → plasma source start trigger. The ESAB ESP-100i accepts a dry contact relay closure on its start input.
6. Wire Arc OK feedback: Plasma source arc-ok relay → controller digital input. This signal tells Mach3 or equivalent that the arc is established before initiating Z-axis pierce.
7. Wire arc voltage for THC: ESAB ESP-100i arc voltage scales via an internal divider to 0–10 V at the THC input connector. Route this to the controller's ADC input labeled Arc Voltage or THC Voltage.

Phase 4 — Mach3 Configuration for Plasma

Assuming Mach3 with a CNC4PC C11G analog output card, configure the following parameters under Config → Ports and Pins → Motor Outputs:

Axis  X:  Step Pin=2  Dir Pin=3  Enabled=Yes
Axis  Y:  Step Pin=4  Dir Pin=5  Enabled=Yes
Axis  Z:  Step Pin=6  Dir Pin=7  Enabled=Yes

Config → Ports and Pins → Signal Configuration:
Input 2 (OEM Trig 2) → Arc OK signal from ESP-100i
Input 3 (OEM Trig 3) → Breakaway / Ohmic sensing

Config → Spindle Setup:
Relay 1 → Torch start (Active Low or Active High per ESP-100i wiring)

Config → Motor Tuning:
X/Y Steps per Unit = (motor steps/rev × microstepping) / (belt ratio × screw pitch)
Velocity ≈ 1500–3000 mm/min for plasma (verify drive max RPM first)
Acceleration ≈ 200–500 mm/s²

Under Config → THC Control, enable Torch Height Control and map the Arc Voltage input to the appropriate ADC channel on your analog card. Set nominal arc voltage target: 120–140 VDC at the torch represents a 1.0–1.5 mm stand-off gap for mild steel cutting.

Phase 5 — Pre-Cut Verification

Before attempting any production cut, perform this sequence:

1. Axis motion test: Jog each axis manually at low speed. Verify smooth motion with no stalling, oscillation, or following error faults.
2. Home sequence: Confirm that each axis finds its home switch and returns to machine zero with repeatability ≤ 0.05 mm.
3. E-stop test: Verify that pressing e-stop de-energizes all drives immediately. If drives coast rather than stop, the enable signal is not hardwired through the e-stop chain—correct this before proceeding.
4. Torch dry run: Lower the Z-axis through its full range with no plasma source connected. Confirm that the floating head tracks without mechanical interference.
5. Single-pierce test: Place a test piece on the table. Execute a single pierce using air only to confirm the torch fires on command, the Arc OK signal activates, and the controller does not report an Arc Fail fault.

Phase 6 — Production Cutting and THC Calibration

With basic motion confirmed, commission the torch height control loop:

1. Set Pierce Height = material thickness × 2.0 (e.g., 6 mm plate → 12 mm pierce height).
2. Set Pierce Delay = 1.0× plate thickness in mm (e.g., 6 mm plate → 600 ms). Insufficient pierce delay causes the arc to blow out during the transition to cut.
3. Set Cut Height = arc voltage target / 100 V per mm (rough guide; calibrate against physical stand-off measurement with a dial indicator).
4. Cut a 100 mm × 100 mm square on 6 mm A36 steel. Measure each side with calipers. Acceptable tolerance for a plasma system is ±0.5 mm per side. Adjust Steps Per Unit if systematic dimensional error exceeds 0.3 mm.

Specifications Summary

Alternative: Complete Drive Replacement

If the existing drives are unidentifiable, non-functional, or lack documentation, a full drive replacement is the most predictable path. Contemporary servo drive sets that interface via step/direction or Ethernet include:

• DMM Technology Servo Systems: Integrated drive+motor packages with step/direction input, open-loop encoder for position verification, and no separate encoder cable. DIN-rail mount.
• Leadshine AC Servo Systems: Closed-loop servo with ±10V or pulse inputs; widely documented with Mach3 and LinuxCNC configuration examples.
• Delta ASDA-B3 Series: Cost-competitive closed-loop servo with Ethernet communication option and built-in position registers.

New drives eliminate the unknown state of undocumented CR Electronic parameters and provide a known-good starting point for tuning.

Notes

No original CR Electronic firmware, configuration backups, or schematics are publicly available. All wiring must be reverse-engineered from the existing cabinet state. If the terminal strips are unlabeled, use a continuity tester and a reference diagram from a comparable plasma table architecture to reconstruct signal paths. The methodology described here is industry-standard and widely supported in the CNC retrofit community.

Frequently Asked Questions