The cutter bit is mainly used to cut soft  working surfaces and collect slag and stones  into the mud bin. It is generally applicable to  loose formations such as silt, fine silty sand,  clay, medium sand, coarse-grained sand and  gravel-containing sand layers. Cutter bits  are usually installed at the openings of the  cutter head and used to excavate most of the cross-section. When the shield machine  advances forward, the cutter bits rotates  with the cutter head and moves forward  slowly. It drives the blade into the soil  through rotational movement and collects  the cut soil into the opening of the cutter  head.