Some of manufacturing tasks such as sawing task often require continuous impulsive motion. In case of sawing task, such impulsive motions can be observed between the teeth of the saw and the object being sawn. The amount of the external impulse exerted on the object is treated as an important control parameter in the sawing task. The purpose of this work is to show the efficacy of sawing task by using a dual-arm. For this, a new concept of effective mass is introduced to model the impact phenomenon in the sawing task. Using this concept, the external impulse model of sawing tasks is suggested. The optimal sawing region is identified in which the amount of external impulse is maximized. It is demonstrated through simulation and experiment that the dual-arm exhibits better sawing performance over a single arm in aspects of external impulse.