The drill string system is a huge and complex mechanical machine that is used to drill wells for exploring oil and gas. Avoiding the undesired vibrations in the drill string is one of the essential contributions of scientific research. In this paper, an experimental setup is prepared to simulate the contact phenomenon in the drill string system. A G.U.N.T (PT500) fault demonstrator laboratory rig is used to simulate a horizontal drill string system. This study demonstrates the influence of changing operating speed parameter on contact characteristics and lateral vibration response. Experiments show that a very small increase in the operating speed affects the intensity of chaotic response. Moreover, FFT spectra illustrate several sub-harmonic and super harmonic components of the rotor system.