Need help with unexpected/random stops on basic Parport/5 axis BOB setup

Your friend is right, but in this case if all is wired properly it should not matter as the BOB is used for exactly that : Isolation.
Give it some more time on the outer socket, it looks like there is an issue with grounding, after all.

Hello again,

I've been able to work with the CNC for a couple hours, and did not see any unexpected stops.

I've left the workshop now, but left the machine ON, so that I'll be able to check it again tomorrow : if all is well, it should still be ON. I've seen (or rather heard the click on the Z axis motor brake) go OFF even when it was completely idle, with no spindle running, no moves etc...

Crossing my fingers at the moment, more tomorrow.

Thanks again, it's great to have experienced people to help !

Hello again,

Went to the shop this morning and was happy to see that the CNC was still ON. We might be on the way to something...

To push things further, I've launched a 2.5 hours .ngc file, with no stock and no mill, so I'll go back later to see whether the machine has completed it or not. Fingers crossed !

I must admit that it all sounds like black magic to me, if anybody can point me to resources that could help improve my understanding of these EMI, GND things, I'd be happy.

Thanks for taking the time to read me

Lezard wrote: I must admit that it all sounds like black magic to me, if anybody can point me to resources that could help improve my understanding of these EMI, GND things, I'd be happy.

It does seem like black magic, but it is not. As with god or love, it is hard to explain things that can not be seen or touched or played with.
Everything that uses electricity uses wires for that electricity to pass through, and while that is happening there are drops in voltage depending on the current flowing through them, that in turn will produce magnetic fields around those cables and that magnetic field will induce current to other nearby wires causing interference. The amount and frequency of those interference's will wary a lot, depending on a lot of factors, way to much to list them here. That is why it is a challenge to find the source of those problems in electronics, especially when having low level signals with high power equipment in the same machine.
Use of shielded cables and proper grounding is imperative for proper functioning of machines.
linuxcnc.org/docs/html/integrator/wiring.html

Hello again,

Just came back from the shop, the machine has gone through its big .ngc file without any hiccup, so it seems OK.

So, bottom line is : PC powered from dedicated socket inside the cabinet => trouble
PC powered from a wall socket outside the cabinet, nothing else changed => OK.
I'm going to run a reverse test tomorrow to confirm this.

I don't understand how/why grounding the PC to another ground (?) makes such a difference. They are all connected to the same electrical panel in the shop... ? :blink:

Hello,

I've tried to power the Bob with a simple 5V power supply, rather than the PC's USB, and power the PC from its dedicated power socket inside the CNC cabinet : same results, the machine goes OFF on its own, after some variable time.
I've noticed also that the PC screen is a bit unstable, with some sort of diagonal ripples going through the image.

With the PC powered from the outside wall socket, all seems well.

At least, I have now a setup that will work, but I'd like to get a better understanding of this. When building the cabinet, we have paid attention and tried to provide proper grounding. All the 'noisy' cables, from the vars to the servos, are double-shielded, with braids connected to the cabinet back plate through an alloy plate and purpose-made cover.

What can I do to try and isolate the source of the problems ?
Thank you for your help,
Laurent