I don't even like people talking about front and side - I'm not sure which is which! I'm sure opinions differ... For me, the long axis is X and short, gantry, axis is Y. Already we have upset the north American community who tend to use the opposite convention. I stand facing the long side with the gantry home position to my left and which makes the LH corner nearest me the natural 0,0 place. Feels right as well as it matches the usual axis layout you would see in a graph. It also means that the spindle is close to hand for tool-changing when it's in the home position. But as long as you know how your CAD/CAM process maps to the bed of your machine, this is all a bit arbitrary and you can decide for yourself which axis is X and so on, and what's convenient for home switch positions.