Zenbot/Gecko/LinuxCNC?

Just because LinuxCNC _can_ be complicated doesn't mean it has to be.

For a simple machine using the parallel port (yes, I know, bear with me) the Stepconf Wizard will get a machine up and running in a few minutes.
If you are using Mesa cards that are supported by PnCConf then the same is true there. If you are using something from Mesa that PnCConf hasn't quite caught up with yet, then it is a bit harder, admittedly.

For other hardware configs you generally just have to edit the INI file of a sample config that is set up for the same hardware. (limits and speeds, mainly).

You say that the LinuxCNC docs are limited. Perhaps you just haven't found them all?
linuxcnc.org/docs/2.7/html/

A drawback of UCCNC is that you are tied in to a particular hardware. If that fails and the company has gone bust, then what?

I think your assessment of Mac3 is fair. Its clearly had its day and I'm not using it for the same reason.
I can't comment about UCNC but I do see a lot of threads on other forums recommending using it. I did not know it existed when I started. Hewre's one last shot at convincing you but ultimately, you are making the decision.

Installing a preempt_rt image and Linuxcnc is simple. You just need to grab one of these ISO's
www.linuxcnc.org/testing-stretch-rtpreempt/

Because you have an existing machine, configuration is probably not that bad. I think the other thing in your favour is that you have a conventional milling machine and therefore won't need to push the envelope when building your machine like I had to with a plasma machine.
I've not used it but there is a Mach3 converter in stepconf that will build an equivalent config for a parallel port that takes the XML file as input.
Its not going to work for a Mesa based machine but it might be very useful as a reference files.

With Mesa you need to use pncconf to create your initial config but it is also very comprehensive. pncconf has recently been enhanced to give better gantry support (but those features might require using version 2.8 - which you can load from the Synaptics package manager if you follow the docs).

Whilst its very different to Mach3, the Gmoccapy interface is very nice to use and I doubt you'd need to modify it. The new version of pncconf allows your to select the interface from a drop down but its only a 1 line ini file change later.

Before you make your final decision, I'd suggest you at least install one of those ISOs and have a play with some of the many included simulators (or SIMs). Any hardware would suffice for the SIMs as you are not driving real hardware in real time. See if you can generate a config from you mach XML and review the generated INI and HAL files.

rodw wrote: Before you make your final decision, I'd suggest you at least install one of those ISOs and have a play with some of the many included simulators (or SIMs). Any hardware would suffice for the SIMs as you are not driving real hardware in real time. See if you can generate a config from you mach XML and review the generated INI and HAL files.

Good point.

You can download the ISO and boot any PC from that (without installing) and see how far you get with configuring your machine with imaginary Mesa cards. (the config wizard does not actually check that the hardware exists).

So you can try LinuxCNC for free and without making any changes to any existing PCs (or similar devices, but for messing about with LiveDVDs and sim configs you might as well use a desktop PC)

Excellent. I'll do just that. I did find the Mesa configuration wizard but it said is was beta and I shouldn't count on it. (Out of date documentation?).

Thanks for info on the iso with the RT kernel already installed. That was another stumbling block.

Finally, I'll look at Cmoccapy. I'm not too picky, but I need to be able to do automatic Z touch off at least based on a probe. Does it do that?

OK so I lied, there is one more finally. I'd like to buy an MPG that is pretty much plug and play.

jandyman wrote: Excellent. I'll do just that. I did find the Mesa configuration wizard but it said is was beta and I shouldn't count on it. (Out of date documentation?). .

More a fear of over-promising on a bit of software that can never be tested on all possible hardware.

Just looked at Gmoccapy real quick. It looks like it does do Z autozero but not the way I want to do it. I want to put a conductive plate of known thickness on top of my stock. The router is connected to the other conductor so the bit is too. I might eventually go with something with a separate tool change block, but not yet. I certainly want both options.