A simple strategy for the reduction of vibrations during robotic milling is proposed. Here, the vibrations are reduced through a sinusoidal variation of the spindle speed as has been done in machine tools. Experimental results show a significant reduction in the measured forces. Furthermore, an improvement of the generated surfaces through modulation of the spindle speed is observed. Based on the experimental results, a simple empirically-based control strategy for the on-line detection and reduction of vibrations through spindle speed modulation is implemented. On-line detection of vibrations is achieved through comparison of the measured and the expected forces, which are calculated using a mechanistic milling force model.