The jaw crusher is composed of a fixed jaw plate installed in the main body of the crusher and a movable jaw plate installed on the jaw frame. There are cheek plates installed inside the diesel jaw crusher as additional wear parts to protect the main crusher.
The two jaws are V-shaped, narrowing the space from top to bottom. The angle inside the V shape is called the press-in angle. An elliptical motion is provided by an eccentric shaft through the top of the jawstock, which is centered around a toggle plate in the lower half of the jawstock.
This geometry turns the rotary motion of the eccentric shaft into a back and forth motion creating the crushing action at the bottom of the jaw. The material is then compressed between the two jaws, reducing in size as it travels lower in the crushing chamber until it exits at the bottom.
By adjusting the gap between the fixed jaw and the moving jaw, the output size of the material can be changed. This is called CSS (Closed Side Setting) and is usually measured between the peak of one jaw and the trough of the other.