Rotor unbalance is the most common reason in machine vibrations. A very small amount of unbalance may cause severe problem in high speed rotating machines 4. Rotor is considered as a single mass in the form of a point mass, a rigid disc or a long rigid shaft 5. Rotor unbalance is a condition in which the centre of mass of a rotating assembly, typically the shaft and its fixed components like disks and blades etc. is not coincident with the centre of rotation. The vibration caused by unbalance may destroy critical parts of the machine, such as bearings, seals, gears and couplings 6. Fig. 1 shows vibration test-rig done by Nikhil T. et al. where the force vibration come from the rotation of an eccentric mass mounted on disc around the variable speed DC motor shaft 7.