The BTA deep-hole drilling process is used to manufacture holes with a high length-to-diameter ratio of up to 100. A major quality criteria is the difference between the drilled hole axis and the desired, ideal straight hole axis, called center deviation. A novel measuring system is being investigated in order to measure the center deviation simultaneously to the drilling process. The deviation is determined by calculating the bending line of the boring bar using a newly developed algorithm. The measuring system consists of four subsystems: Optical fiber Bragg grating (FBG) sensors, four eddy current sensors, a rotary encoder and a displacement encoder. These subsystems enable a spatial measurement visualization of the bending line and the center deviation at the head of the boring bar. A major challenge is the separation of the bending strain from other undesired strain fractions. This is done by using an arrangement of two FBG sensors and a digital band pass filter. Experimental investigations show sufficiently good agreement between the calculated and the actual center deviation. Furthermore, drilling experiments reveal that the measurement setup can be used for additional process monitoring by using frequency analysis. Therefore, the investigated system is able to visualize and observe the center deviation. The visualization can be used to derive adequate countermeasures in order to ensure a better process control for the machine operator. The objective of the investigation is to increase the process reliability and productivity by preventing scrap parts. Within this paper, the investigated measuring system, the calculation of the center deviation and first experimental results are described.