pipertzisdimitris:
Ok.Lets start from the beginning.My idea was to make a cnc machin with 4 spindles.
It would help if you explain what you mean by "spindle" in case we are misunderstanding you.
If you have a single machine with 4 different tools I don't see a need for 4 Arduinos. And if there is only one Arduino then I would expect that the GCode could easily specify which tool is to be used - that is a common requirement with high-end CNC machines.
Of course another approach would be to interpret the GCode on the PC and then it could send commands for movements to different Arduinos.
If you tell us what the CNC machine is for and maybe provide a diagram of it then it will be much easier to help.
...R