Often when the jigsaw vibrates, it is because of the process of application. A jigsaw is a power tool working against a surface, whether hard or not. For hard surfaces, the chances of vibration occurring is high, as the device will be grinding against a tough surface. So, the combination of the forces and movement during this process is often what leads to vibration. So, if your jigsaw is vibrating, you most likely have no reason to worry.