A typical boring bar is a metal cutting tool with low dynamic stiffness, and is therefore susceptible to excessive vibration during the metal cutting process. The use of an active dynamic absorber as a viable means of actively suppressing vibrations in a boring bar is studied in this paper. The boring bar with an active dynamic absorber is modelled as a two degree of freedom lumped mass system. The dynamic equations of this system are calculated from the experimental frequency response function data of the overall system. These equations are posed as a Linear Quadratic Regulator (LQR) problem, and optimal control theory is used to calculate the state variable feedback parameters. These feedback parameters are implemented in the experimental setup. The experimental results are obtained for different length to diameter ratios of the boring bar and compared with the theoretical results.