A motorized high speed spindle has very complicated dynamics consisting of non-stationary and speed-related thermal characteristics. Many studies have been reported with different designs to control or monitor spindle's thermal growth with limited results, whereas the application of High Speed Machining (HSM) demands "zero tolerance" no matter the range of speed or material to be machined. This paper proposes a direct displacement measuring system, which is a considerable improvement as compared with many taking inaccurate readings through a traditional thermo coupler, to accurately monitor and compensate the thermal growth associated with motorized high speed spindles. This direct displacement measuring system optimizing a high speed synchronous feedback system will meet the tolerance and performance expected in HSM applications. Based on the introduction of Foucault current, a design for an accurate thermal growth is outlined.