This is the model used for the animation...
Note the Z axis move with it's base as the rail guides for the X axis. The Y axis only has to support the spindle and not the Z axis too...
The Z axis will need dual drives.
The X axis does move well with the force applied at the center, however, I may do dual drives here alos to prevent torque.
The 4th axis (A or W?) works with torque applied to the base through a rod and pulley connected to the motor, and the top moves along a cam follower.
Larger view..