Machine components that hold a workpiece (part and/or stock) require special definition in the machine assembly. This is so that Machine Simulation knows how to position the workpiece during simulation. A special machine component called a Part Body (P-body for short) must be defined in the machine assembly. The P-body does not have an axis, meaning that if it moves during simulation, it is a result of being attached to another component that moves.
The P-body is a machine component made from any solid body (usually a cylinder or a rectangular solid) and is given an label of P or Px, where x is any integer number. This special P naming tells machine simulation that the P-body is not to be displayed directly in the simulation, but the P-body is to be replaced by the actual machined part/stock during the simulation.
For a mill it is typical that the P-body is a child of the machine component representing the machine’s table, meaning that it is attached to the table.
For a lathe, it is typical that the P-body is a child of the machine component representing the machine’s part spindle (or collet, bushing, or chuck).