The future of manufacturing will increasingly depend on the autonomous operation of machining systems. Currently, most machine tools lack the capability to adjust their structural properties, such as stiffness and damping, limiting their adaptability to changing machining conditions. A lathe spindle with adjustable stiffness was therefore developed to eliminate this impediment. This design of controlled preload of a front-bearing node allowed modifications of the spindle's static and dynamic properties. This innovation aims to create a mechatronic system that facilitates autonomous machining by adjusting spindle stiffness. This would result in (i) enhanced manufacturing accuracy, (ii) compensation for workpiece deflection, and (iii) suppression of self-excited vibrations during turning. The paper details the spindle structure concept, the finite element model calculations of the bearing node with its adjustable stiffness, and the results of experimental testing of a prototype. The proof of concept demonstrated that spindle stiffness could be increased by approximate to 10% by changing the preload from low to high.