What are the max angles of human eyeball rotation?
There shall be slight differences due to physiology. Nevertheless, the average vertical ascending angle is 25 degrees and descending angle, 30 degrees.
Within the x-y plane of which we assume to be coplanar with the central line of vision, the maximal angle of rotation is 35 degrees in the left and right directions respectively. 



I attempted to construct an image which depicts these angles - simply a Cartesian diagram. 
You can find further clarification of details from this link by Nelson &amp; Associates   

Finally, it is important to note that although the eye may be capable of these rotations, the eye may not be able focus on all objects in this field acutely, namely, focusing light on the fovea.

Happy muscular experiments.