Time-controlled grinding technology enables deterministic machining by precisely controlling the grinding time of the grinding tool at different positions on the workpiece surface. This technology can significantly improve the shape accuracy of shaft parts, but there are machining limits. In this paper, from the perspective of the removal function of time-controlled grinding, the influence of the removal function size on time-controlled grinding processing is discussed, and the machining accuracy of the mandrel is improved by optimizing the removal function and machining process. First, the removal function models of different sizes are established, and the machining simulation of the same initial face shape is carried out to analyze the influence of the removal function size on time-controlled grinding. Then, based on the analyzed results, the time-controlled grinding device was improved and the removal function models of two different sizes were established by experiment. Finally, a mandrel was time-controlled ground using large and small removal functions in turn. The results show that the larger size of the removal function has a higher machining efficiency, and the smaller size of the removal function has a higher machining accuracy. After time-controlled grinding, the average roundness error of the mandrel converges from 0.244 μm to 0.128 μm, and finally to 0.110 μm; the cylindricity error converges from 0.589 μm to 0.573 μm, and finally to 0.381 μm. The combination of the machining process with the large-size and small-size removing functions not only ensures the machining efficiency, but also significantly improves the machining accuracy.