Post-editing comparison: Text provided to models

This is the text we passed to the three models when comparing post-editing models. It is a direct copy of Control and Electrical Configuration as it was during the test on 2026-11-05. The text was sent to the models heading by heading (h2), with tags and headings replaced by marks like ⟦number⟧. The comparison results can be found in "Comparing models" under Document Post-Editing (Gemini).

Control is handled by LinuxCNC and a Mesa Ethernet card. The deciding factor was being able to use rigid tapping (G33.1). The 7I76EU is our candidate card (research from 2026-11). Values are read from manuals and sales pages, and combinations will be verified on the actual machine.

Control software comparison

Card selection

• Spindle-related performance is the same between the 7I76EU and 7I96S. The only difference is the number of I/O points.
• This machine needs at least 11 inputs, so the 7I96S would be maxed out on day one. The 7I84U expansion card (US$79) is out of stock, and adding it makes the setup more expensive than the 7I76EU.
• We found no newer cards that would change our decision. The "T" in the name indicates an improved version of an existing card, not a higher generation.
• If you want to drive 2 A outputs directly, the 7I96S is well suited. With the 7I76EU's 500 mA outputs, solenoid valves and the brake (0.18 A) are expected to be sufficient.

Notes on the 7I76EU

• LinuxCNC 2.9.3 or later is required. Use a newer version of mesaflash as well. There are reports of versions where PnCConf is not supported, so assume config files will need manual editing.
• To maintain isolation, keep the 24 V and logic-side power supplies separate (sharing them removes isolation).
• General-purpose I/O and the analog spindle are isolated; step, direction, encoder, and RS-422 rely on differential signaling for noise immunity. Near welding equipment, chassis grounding of the board and shielding are critical.
• Inputs are sinking only. NPN sensors require a pull-up resistor (2.2 kΩ).
• Board dimensions are unverified. Confirm them before laying out the enclosure.

Spindle commands

• Plan A: Drive the A6 servo with step/direction. This avoids the need for a ±10 V dual power supply and eliminates the issue of analog outputs latching at startup.
• LinuxCNC's stepgen is used in velocity mode. Spindle orientation switches to PID output via mux.
• Actual spindle rotation is read by the card's encoder input after dividing the servo's A/B output frequency. Setting it to 1250 lines gives 500 kHz at 6000 rpm. Near welding equipment, avoid setting the line count too high so the input filter remains effective.
• For the index, add a 1-pulse-per-revolution sensor to the spindle. With a 2:1 reduction ratio, the servo's Z pulse occurs twice per spindle revolution. Combining A/B from the servo with Z from the spindle sensor is recommended by Mesa engineers on the LinuxCNC forum and has proven working examples (7I76 + 7I83, 1:1.8 reduction, M3–M6). Feed the signal as a 5 V system.
• There are reports of machines shaking and tripping overvoltage errors when pulses are stopped abruptly. Set the stepgen acceleration and test this first, along with the A6 regenerative resistor.
• Set the servo torque limit to approximately 6 N·m. This prevents instantaneous belt force from exceeding the shaft's allowable load (Purchased Part Specifications and Dimensions).
• Unverified: We found no direct reports of successful rigid tapping with a servo spindle using the combination of 7I76EU, 7I96S, and A6-RS. There are reports for older 7I76-series cards, and since the spindle functions share the same specs, it is expected to work. Asking on the LinuxCNC forum before ordering would be worthwhile.
• For details on using G33.1, wiring signals, tool holders, and commissioning procedures, see How to Use Rigid Tapping.

Inputs and outputs

Outputs use 5 points: servo enable, tool release solenoid valve, air blow, orientation command, and coolant. Driver alarms, rack sensors, and control buttons can be added using the remaining outputs.

Power and safety

• Single-phase 200 V. The A6-1000RS requires a 9.6 A input, 20 A fuse, 16 A breaker, and 12 A contactor (per manual).
• The manual specifies a Type B earth leakage circuit breaker with a sensitivity of 100 mA or higher. Confirm with a licensed electrician. Place a dedicated branch breaker upstream of the machine.
• Ensure solid grounding. This is the foundation for handling servo leakage current and electrical noise.
• Because it will be used near welding equipment, include noise filters, signal wire separation, and shielding. Never weld on a workpiece connected to the machine. Welding current risks passing through the bearings and encoder.
• Emergency stop relies primarily on physical interruption via contactors. Circuit is not yet designed.

Future ideas

There is an idea to write human-facing routines as custom commands that convert to G-code. This is well suited for repetitive tasks like hole arrays, pilot holes, and tapping. We will decide on this after the machine is completed.