VFD is blowing my RCD

[Mr*Beaver]

Eh?, I'm a little confused - I'm assuming that you have an adequately earthed connection to the machine?, my next thoughts would be how the supply earth is exported to the garage - whether through a 3-core cable or a local earth rod... but you're clear that the trip also occurred in the house and that the RCD circuit is okay, so I won't pursue that.

What do you mean by grounding the machine earth through an additional PSU - currently laptop power - I'm not aware of a laptop PSU that exports an earth - I'm guessing from the language that you've connected the negative supply to the machine earth??, if that's the case then that isn't earthing the machine and this could be a cause of your problem. Absolutely provide a low-impedance earth strap from the machine to the garage supply earth. Also - from your picture of the machine - make sure that all exposed metalwork has a reliable earthing.

Well the machine and all the machines metal parts are earthed so the spindle, power supplies for the drivers etc all go to earth - being in the UK almost everything here is earthed. In my garage this comes through 3 core cable. The spindle has also been earthed by myself and this runs through the spindle cable.

However the electronics box/machine case, ardunio, relay are not earthed... I can work out the machine case but I'm not sure how you earth a arduino board?

Also the board I'm using is running grbl 1.1