I had time to test some more today.
Let me start with a big thanks for the great, helpful feedback.

I started trying some runs with G33. Multiple runs with the same settings resulted in only one tool mark.
Increasing the RPM did in fact result in a slightly lagging toolpath (cutting on the right side of the insert).
This was not very pronounced, even between 100 and 900 RPM the difference was visible, but not more than a few tenths of a mm.
At 2000 RPM, the new tool marks were close to the middle between the earlier ones. But I don’t really intend to thread at 2000 RPM anyway.

Going back to G76, but with Q, H, E, and L all set to 0, gave me my first nice thread.
Reintroducing Q29 still gives a nice thread and cuts on the left of the insert, as one would expect.
H2 also still worked, and after that E0.75 but L0 gave the same good result.
So only L2 was left, and I am now using the same G76 line as before, so this has to be the problem.
But no it also cuts fine.

At this point, I am uncertain if I should be happy that I can cut threads now or worried that I have no idea what was wrong until now.
I cannot think of anything I changed in between.The only thing is, I had a look at the belt connecting the spindle to the encoder.
I had this apart and inspected, checked the belt (nothing notable to see), and put it back together. I don’t think that should have changed anything, maybe slightly different belt tension?

check the angle on the bar, and be sure of your tip height, both will break most threading insert, been there got the t shirt

This appeares to be working now
checkout  the state-tags-arc from my repo to test
github.com/rodw-au/linuxcnc/tree/state-tags-arcs

There is some house keeping to sort out. I need to work out how to use equate G_1,G_2  etc in motion (control.c) I remember the devs last time I tried, they did not like this  but I have not got a solution yet. Its just housekeeping and will only be an issue ig the equates for gcodes are ever changed.

Have you run linuxcnc from a terminal so you can see any errors?
you need python3-zmq package on the system.

macros are defined under heading:
[DISPLAY]
MACRO=
MACRO=

I'll have to check later to confirm all work properly.

Thank you, Peter.
I did as you suggested and I was able to see the dio listed in halshow.
I spent all day trying to understand how to access and setup the inputs and outputs using the M64+ commands.
I think I figured it out after hours of frustration.
My issue was understanding the syntax of how the actual screw terminals of the 7I77 connected to the input of an MDI command of say M64 P4.
I needed to get my head around the random name that I had assigned to an output [ say Digital out 4], the terminal on the 7i77 ( that could be terminal 8..) and the call sign [say M64 P3] that i put into MDI . Understanding how to link them all together in hal to get a predictable result was a head-wreck.

Watching that single halshow dot finally turn from brown to yellow made my day.
Easy once you know.....as usual.

Thanks.

andypugh wrote:

Having looked at this a few times, I think that the best place to do it is actually in a G-code filter. ie calculate the heading from the G-code and insert / append C axis moves as appropriate.

Actually, there is a use case that needs motion pins. A plasma cutter cutting bevels. An additional joint is needed to tilt the torch and there are complicated tilting torch holders that keep the torch tip axial to the Z axis (single axis bevel head). I was just chatting to a user with one who uses the post processor approach.

But picture a simpler torch holder design where the torch tip position moves when tilted. A component could take the bevel angle and calculate the offset x,y,z positions of the tilted torch tip and then apply external offsets to locate the torch on the cut path in real time. This way, the machine could consume simple 2D x,y gcode (which is the norm for plasma cutters) and enter plasma cutting nirvana with bevelled holes.

I found a situation with inductive sensors where default input threshold of 3.5 V is to low, as those sensors are 4.5-5.5 V in OFF state.
For one sensor I mitigated it with adding 10K pulldown resistor. Is there any better way to do that?

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Tom I came across your videos looking for information on a Messer plasma table. I have an older machine year 2000 that I bought from a John Deere factory in Iowa that was running the day that I purchased it, I am trying to get it up and running but don't have software or the computer cables etc to fire it up. Everything is hooked up but its looking for a password. Has an older Navigator control that looks good but I cannot get past the password as I cannot type it in. I do know the password - i just cannot type it in. Messer is no help, they just keep saying it is obsolete. If you could point me in the right direction or be of any help I would greatly appreciate it. Thanks Sean
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image missing https://github.com/b0czek/noHAL/raw/main/docs/public/screenshots/editor.pngHI,
I wanted to share with you a tool I've built to make my life easier and I think it has reached enough maturity to be used as a real tool.
It is be no means perfect and some of it is not as polished as i wish it was, but I thought it'd be nice to have it reach more people.
The project's name is NoHAL and as the same suggests - it's supposed to make you not write HAL anymore.

https://github.com/b0czek/noHAL/blob/main/docs/public/screenshots/editor.png?raw=true

It does that by visualizing HAL network as node editor - with an added benefit of making repetitive parts of your HAL configuration templatable through sheets.
I've built it around what I work with, so it might not match your workflow perfectly but issues/pull requests are open for suggestions.
There is Mesa configuration utility built-in but I've only defined a limited set of boards - only those I have used.

Here's a link to repo with it:
github.com/b0czek/noHAL

And here's a guide I've written on how to use it:
b0czek.github.io/noHAL/

Please let me know what do you think of it.