Special-Purpose Milling Machines.

Special-purpose milling machines are built to accommodate larger work, duplicating parts of work pieces, surfaces the work piece precisely or to do many other unusual milling operations which regular milling machines cannot do. There are three types of special-purpose milling machines.
Planner-type Milling Machines
The tables of these machines carries the work piece across the rotating cutter heads which are dividually powered and the speed of which can be changed. As many as four cutter heads can be used with two mounted on the cross rail and two on the vertical pillars. These type of machines are normally used to machine parts like the bed ways of large machine tools and other long work pieces.
Profile Milling Machine
Two-dimensional profiling can be done by using a template or by controlling the vertical milling machine vertically. Certain types of profilers have several spindles and a number of duplicated parts can be produced for every cycle. Hydraulics-type profilers have a stylus that touches the template when starting the operations. The operator moves the stylus along the template which causes the thet table to move past the cutters thus duplicating the template. Diesinking and other processes that involve machining cavities can be done on 3D profilers.
Jig Borers
Jig borer machines are somewhat similar to vertical milling machines but they are more accurately or more precisely constructed. These kinds of machines are used for boring operations. Some jig borer machines have a digital readout system which is more accurate.