Electrical Noise Causing Axis Jumps

In .AU the neutral wire is bonded to Ground in the building switchboard.
When I went on a noise busting crusade with an oscilloscope, I found that a lot of the noise was entering via the mains ground and a distinctive 50 Hz AC ripple showed up. Fitting an EMI filter on the mains input basically solved all problems.
The other thing I did is follow a guide about plasma cutters from Hypertherm. This involved setting a star ground point on the frame and running a seperate wire from every motor frame back to the star ground point. This guarantees a low impedence path for noise to dissipate. Without this, the noise is exascerbated as it use high impedence paths though your linear bearings that are not firmly connected.
Some higher end steppers have a grounding point on them. I always use them regardless of the machine...

So I think adding the EMI filter is just part of a quality built machine, and definitely not an admission of defeat!

So I finally acquired some parts and got round to doing some more testing on the machine. I installed an EMI filter on the input of the Spindle Drive and a toroid ring on the output as well. All analog and encoder signal wires are now shielded which are correctly grounded.
I started up the spindle and the nuissance tripping and axis jumping continued. Still thinking the position of the head of the machine had an impact on this, I ran a new cable externally from the spindle drive to the motor to see if this was the issue and the problem still persisted. While I was doing this test, the guys at my work turned on either the induction heater or laser ablation system (automation solution we are developing for a customer) and as soon as it turned on the machine threw a fit and tripped stright into an e-stop. Now knowing this occured, the other day when I was running the machine and it was behaving normally was actually when this automation system we are deveopling was all disconnected as we were reolcating it. This is why the issue was present before and after my sccessful machining job and is worse now than it was at the start as more equpiment has been connected to the automation system in the factory.

With all this in mind now, I am not sure what should be next. I know the power supply that supplis the MESA cards and servo tacho generators has a line filter inbuilt but questionable to exactly what it is. I am thinking of getting a 2-stage line filter and putting it on this power supply and one for the 24v pow supply that supplies all sensors on the machine and see if this will help.
I believe the spinde drive is just a small part of this bigger issue as when it turns on the incoming noise must just be reaching a level to cause issues which is amplified as more equipment is powered on within the factory.

I find it quite remarkable that radiated interference has enough energy to trigger opto-inputs. Maybe your induction heater is very "leaky"?

Getting rid of electromagnetic interference is something of a black art. Line filters won't really help with radiated emissions. You can try to minimize the area your circuits span (current always flows in loops, the larger the area those loops span the better antenna they are). Try to avoid "open" inputs, so either use SPST switches or use low-enough pull up/down as appropriate. caveat emptor. IANAEE.

RMU, it my have been the induction heater or the laser ablation system, I think it was the latter but will do a test with the guys this week to try to repeat this. Both these systems are on the other side of the factory ~30m away an on a separate sub-DB to my machine.

My thought process at the moment is when other equipment is on in the factory it is producing noise on the 3PH AC lines and when I start the spindle drive it pulls more current creating more noise which tips it over the edge (I am going to have the induction heater/laser ablation turned on with machine on and spindle drive off to see if it trips again or only with spindle drive on). The machine ran fine milling robot risers flat the other day with no issues or tripping. Once the automation system was reconnected this issue returned. Do note this automation system has 2 robots, conveyor system, laser ablation, induction heting and welding, max amp input is 240A peak.
I need to somehow protect the power supplies for control and sensors from this noise which causes the nuissance trips and axis jumps.