Control and Electrical Configuration

For control, we use LinuxCNC with a Mesa Ethernet card. The deciding factor was being able to use rigid tapping (G33.1). We picked the 7I76EU as our candidate card (researched in 2026-11). Values are read from manuals and sales pages; we will verify the combinations on the actual machine.

Comparison of Control Software

Card Selection

• The spindle-related performance is the same between the 7I76EU and the 7I96S. The only difference is the I/O pin count.
• This machine needs at least 11 inputs, so the 7I96S would be fully occupied on day one. The expansion board 7I84U (US$79) is out of stock, and adding it costs more than the 7I76EU anyway.
• We found no newer cards that would change our decision. The "T" in card names indicates a revised version of an existing card, not a next-generation architecture.
• If you want to drive 2 A outputs directly, the 7I96S is a better fit. With the 7I76EU's 500 mA outputs, we expect solenoid valves and the brake (0.18 A) to be adequately covered.

Notes on the 7I76EU

• Requires LinuxCNC 2.9.3 or higher. Also use a recent version of mesaflash. There are reports of PnCConf versions that do not support it, so assume configuration files must be edited by hand.
• To keep isolation intact, keep the 24 V power supply separate from the logic-side supply (tying them together eliminates isolation).
• Only the general-purpose I/O and analog spindle are isolated; step, direction, encoder, and RS-422 are designed to withstand noise via differential signaling. Near a welder, chassis grounding of the board and shielding are critical.
• Inputs are sinking type only. NPN sensors require a pull-up (2.2 kΩ).
• Board dimensions are unverified. We will confirm them before laying out the electrical cabinet.

Spindle Commands

• First plan: drive the A6 servo via step/direction. This avoids needing a ±10 V dual-rail supply and prevents issues where the analog output locks up at startup.
• LinuxCNC's stepgen runs in velocity mode. For orientation, switch to PID output using a mux.
• To read actual rotation, divide down the servo's A/B outputs and read them via the card's encoder inputs. Dividing down to 1250 lines gives 500 kHz at 6000 rpm. Near a welder, do not aim for excessively high line counts, and leave input filtering intact.
• For the index pulse, add a 1-pulse-per-revolution sensor on the spindle. With a 2:1 reduction, the servo's Z pulse occurs twice per spindle revolution. Combining A/B from the servo and Z from a spindle sensor is recommended by Mesa engineers on the LinuxCNC forum, and proven examples exist (7I76 + 7I83, 1:1.8 reduction, M3–M6). Feed the signal at 5 V logic levels.
• There are reports where stopping pulses abruptly caused machine vibration and triggered overvoltage errors. Configure the stepgen acceleration and test this first along with the A6 regenerative resistor.
• Set the servo torque limit to about 6 N·m, so instantaneous belt tension does not exceed the shaft's allowable load (Purchased Parts Specifications and Dimensions).
• Unverified: We found no direct reports of successful servo spindle rigid tapping using this exact combination of 7I76EU, 7I96S, and A6-RS. Reports exist for the older 7I76 family, and since the spindle functions share the same specs, it is expected to work. Asking on the LinuxCNC forum before ordering would be a good idea.
• For how to use G33.1, signal wiring, holders, and bring-up steps, see How to Use Rigid Tapping.

I/O

Outputs use 5 pins: servo enable, tool release solenoid, air blast, orientation command, and coolant. Drive alarms, tool rack sensors, and operator pushbuttons can be added using the spares.

Power Supply and Safety

• Single-phase 200 V. The A6-1000RS manual specifies 9.6 A input, 20 A fuse, 16 A breaker, and 12 A contactor.
• The manual specifies a Type B earth leakage circuit breaker (ELCB) with sensitivity of 100 mA or higher. Verify with a licensed electrician. Place a dedicated branch circuit breaker upstream of the machine.
• Ensure solid grounding. It is the foundation for managing servo leakage current and electrical noise.
• Because it will operate near a welder, add noise filters, separate signal lines, and use shielding. Do not weld on workpieces connected to the machine; welding currents could pass through bearings or encoders.
• E-stop primarily relies on physical disconnection via a contactor. Circuit design is pending.

Future Ideas

There is an idea to write human-authored routines in custom commands and convert them to G-code. This fits repetitive tasks like hole patterns, pilot holes, and tapping. We will decide after completing the machine.