Ok, great, i'll likely use 12mm ally then as its a good size for counter-boring bolt heads etc. The Y bracket I am sketching up at about 350mm long with the motor beneath the knee at about 5 o'clock angle.
The X axis will likely be towards the rear or below but the motor will probably have to stick out the end as most do due to it's size, this makes mounting harder but will not fit under the table as it hits the knee.