A portal milling machine is a type of machine tool that uses a horizontally-oriented spindle to remove material from a workpiece. The spindle is mounted on a movable portal that can move along the X, Y, and Z axes, allowing the machine to create complex shapes and geometries.

A portal milling machine typically consists of a bed, a portal, and a spindle head. The bed supports the workpiece during the machining process, while the portal moves the spindle head along the X and Y axes. The spindle head moves along the Z axis to control the depth of cut. The machine is typically controlled by a computer numerical control (CNC) system, which allows for precise and automated movement of the portal and spindle head.

Portal milling machines are typically used for cutting large, heavy parts, such as those used in the aerospace, automotive, and construction industries. They are also used in the production of machine parts, molds, and dies, and in the machining of large structural components. They are large machines and take up a lot of space in a factory floor, but they offer high precision and a large work envelope compared to other types of milling machines.