Computer numerical control (CNC) lathes are optimized for machining workpieces into rotating shafts or cylindrical shapes of structures. However, because rotating mechanical parts are used on CNC lathes, vibration from spindles, servomotors, hydraulic pumps, and feed screws occurs. Therefore, periodic preventive maintenance is required to minimize vibrations. Additionally, alignment, balance, and adjustment operations are necessary for parts that perform linear or rotational movements. Thus, this study adjusts the tension of the V-belt that drives the spindle of the CNC lathe, analyzes the primary components and the vibrations occurring at the spindle and servomotor, and measures the surface roughness to identify the cutting quality according to the impact of the belt tension. The experimental results show that the peak value of the vibrating component increases as the cutting speed increases. We demonstrate that the optimal vibration characteristics and excellent surface roughness values are achieved at a relatively looser belt tension than the standard value. In particular, at a feed speed of 0.05 mm/rev, a cutting speed of 250 m/min, and a depth of cut of 0.8, the surface roughness in loose tension was reduced by up to 143.9% compared to tight tension. Additionally, the optimum processing quality is achieved at a cutting depth of 0.6 and 0.8 mm, corresponding to a turning insert nose R-value of 0.4 mm, and at cutting speeds ranging from 200 to 250 m/min.