What do I need to switch to LinuxCNC

Back to the Mesa cards. I've so far been unsuccessful in getting Mesa on the phone to discuss these cards. Please forgive me if I'm using the wrong lingo.

There is a 7192H card that appears to be a direct replacement for my existing ESS (Ethernet Smooth Stepper) and would attach to my existing PMDX 126 breakout board. Then there is the 7176E this would replace my ESS & Breakout board. As the 7176E would replace my PMDX 126, I think I'd have to rewire everything, but I notice 2 parallel port looking headers on it. Could I tie those 2 headers to my PMDX 126 board while I'm evaluating this solution and eliminate the extra BOB later after I've committed to the switch? While I really want to make LinuxCNC my new solution, I also want to be able to easily revert should it not work out. Or if I urgently need to make a part while I'm still figuring out Linux CNC? I'm hopping I can just switch PC's pull the mesa card plug the ESS back in and be running windows and Mach again. I also see Mesa has card slot solutions this is not ideal for the Micro PC I'd like to use, but if this were the hot ticket, I'll certainly but a PC that has slots. Again I'm looking for the best possible solution and I'm not worried about a couple hundred bucks. I have this Bridgeport Mill and also a CNC Plasma table I'll convert next if all goes well.

The next question relates to the real time kernel you Linux guys always brag on. If I understand correctly with my Mach3/ESS combo (Not old school windows parallel ports), the ESS is doing most of the work of course plotting and generating all of the step and dir signals and windows gets updated as to the ESS results as Windows allows. This way the ESS offloads the important work from windows preventing issues with windows being distracted with other running processes.

Again If I understand correctly on Linux CNC, the Linux kernel retains full control of motion plotting. It's my understanding that this is good and necessary for things like rigid tapping, but other tasks running on the same machine could have a larger effect distracting the Linux kernel. Is this an accurate statement? If I'm wrong please correct me.

I forgot to mention, I have Gecko 203V drives for my Nema 42 steppers and a Teco JNEV-203-H1 VFD for my spindle.

What drives and motors you have is mostly irrelevant. What kind of signals are used to control them are all that matter, and if you were controlling them with Mach, they are using simple step/dir for the axis and something equally as simple and standard for the VFD (probably pwm/dir.)

Yes you could connect to the 7i76e using the 2 parallel port headers and not use the normal machine connections. You would be essentially using it as a 7i92. But while you are doing so you also are wasting the $110 of additional hardware you got when you purchased the 7i76e instead of the 7i92. The main advantages of the 7i76e over using your pmdx126 are, the step/dir outputs can be true differential signals for better noise immunity and the 48 isolated field io points are rated for 5-28v. so they can be used with standard 24v signals for better noise immunity.

But if you are happy with the pmdx126, don't want to rewire the machine, and want to keep compatibility with Mach, why bother spending the extra money on the 7i76.

As a side note, I think it could be theoretically possible to create a firmware that could be flashed to the Ethernet Smooth Stepper, that would make it Linuxcnc compatible and work like a Mesa card. From a hardware stand point they seem very similar to Mesa's Ethernet boards. But it will require a programming tool and if you don't know what your doing I think the chances of bricking your ESS are pretty high.

Its great that you are digging through this stuff and taking the time to understand the differences. The cheapest option to trial Linuxcnc on your machine would be to grab an older Corporate DELL or HP PC (Tommy can guide you there) as your Linuxcnc box and simply plug your PMDX126 directly into the parallel port on the PC. There is even a tool that allows you to import your Mach XML config into Linuxcnc.

To do this requires the step pulses to be generated in the PC via a second and faster thread (we call it the base thread). There will be restrictions on how fast the motors can be driven that may not be an issue on a machine like yours. The advantage of the Mesa cards is that it removes the stepgen function from software and runs it on external hardware so the base thread is no longer required. This substantially relaxes the real time demands of the OS so the latency is not as important. This then allows the use of the smaller more modern PC's that are polluted with power saving features that are bad for latency (We generally switch them off in the BIOS as part of preparing a PC for Linuxcnc.)

Then if you find that you like Linuxcnc, bypass the 7i92 option, bite the bullet with a 7i76e and rewire your machine. As said, that gets you up into a much more industrial electronic platform running industry standard 24 volt logic signals for field power which is much more immune to electrical noise than 5V or 12V logic systems you are accustomed to. A suitable power supply (say a 2 amp 24V Meanwell) will only set you back $30-$50 but you may need to change out some relays if signals are beyond the current handling capabilities of the Mesa Outputs.

I pulled the trigger and ordered the Mesa 7I76E. I'm hoping to try it first using the 2 26 pin headers to my breakout board, then once I prove it's a keeper, then I'll rewire the machine to fully utilize the 7I76E.

Remember you will may need a custom firmware. TBH I haven't looked deeply into 7i76e firmware.

Isn't this board intended for Linux CNC? Why would I need custom firmware and how would I get it?

Yes, yes it is,
But the firmware would be to enable pins on the expansion connectors to have different functions.
Usually the firmware zip files, well at least for the 7i92, has the actual bitfile files and another file that describes the usage on the pins for each port dependant on the firmware you have loaded. Unfortunately while bitfiles are there there are no pin files describing the functions of what the expansion port pins would do.