With the development of production processes over the last decades, machine tools have evolved, and in everyday life today it is impossible not to visualize the new facilities arising from technological developments, such as IoT (Internet of Things) systems. Because they are so relevant, they have become a competitive differential in all markets and will not be different in the transformation industry or in its operational areas. Estimating when any machine will fail beforehand is fundamental to maximizing the company's results and consequently minimizing operating costs. In this sense, this research aimed to develop an IoT system for the online management of machine tool spindles in operation and to provide reliable data for maintenance management in the context of Industry 4.0 (I4.0). The development of the system took place through the Design Science Research (DSR) methodology. Thus, with the systematic review of the literature, the artifact/theoretical system of the method type for online monitoring of spindles in operation was developed, and its implementation was demonstrated and validated via a case study with participant observation in an automotive industry. The main contributions of the research are the artifact/system developed and validated and the associated predictive maintenance method. With the artifact, the normal behavior of the spindles in operation is demonstrated, contributing both to the academy eld and to the practice in the industry, in the sense of advancing knowledge and preventing catastrophic failures in machine tools.