When CNC was first invented it was a technology that was adapted to fit existing machines. Today CNC technology is still being retrofitted to various machine tools but there are also many machines which are created for the sole purpose of being CNC machines.
Machines That Are Retrofitted
Milling machines are often retrofitted with CNC technology.
This process involves removing all the mechanisms built into the machine to make it easy for a human to operate, such as: hand wheels and DRO (Digital Read Out) electronics.
The machine will usually have its old lead screws replaced with very high accuracy ball screws and various new mounts built for mounting the actuators (stepper or servo motors) to the machine.
Just like milling machines, lathes are also commonly retrofitted with CNC technology in the exact same way.
Machines That Are Custom Built For CNC Operation
CNC Routers are a very common piece of machinery you will see a lot when learning about CNC.
These are machines built exclusively to be operated by CNC technology and typically have no human interface other than through the computer.
Routers are generally for producing larger dimension parts and more commonly built with the idea of cutting wood, plastics and sheet metal in mind. Routers also are most commonly found in a 3 axis Cartesian coordinate setup (X, Y and Z). A 3 axis set up will allow cutting of profiles, pocketing and 3 dimensional relief machining.
There are also CNC routers which are 4, 5 or even 6 axis (the additional axes are rotary and used to rotate the tool around the work piece or visa versa), these machines are more suited towards cutting more complex shapes or prototype models.
There are many milling machines today which were built specifically for CNC as opposed to being retrofitted at a later stage.
Some of these machines are absolutely massive, have built in tool changers, auto-feed mechanisms for loading in material and various electrical sensors for safe monitored machining.
CNC Plasma Cutter
CNC plasma cutters are very similar to CNC routers in size and setup.
However plasma cutters don’t require as much of a powerful set up because as opposed to dragging around a spinning tool in material they fly above the table with a plasma torch.
Plasma cutters are made for cutting 2 dimensional profile shapes into sheet metal.
CNC Laser Cutter
CNC laser cutters follow the same principle as the plasma cutter, except they use a powerful laser to do the cutting. Laser cutters are often good for cutting wood, plastic and metal; each will need a different strength of laser suited for the material depending on the hardness and thickness.
A 3D printer uses a similar set up as a CNC router or laser cutter, but unlike those machines it does additive machine as opposed to subtractive machining.
Instead of starting with a solid piece of material and removing bits of that material to end up with the desired part, the 3D printer starts with a blank canvas and builds a part up layer-by-layer.
The 3D printer does this either by using an extruder that pushes a material (typically plastic) out from a tiny nozzle, or by using a laser that quickly solidifies a powder or liquid.
Pick and Place Machine
A pick and place machine again uses a similar set up as a CNC router or laser cutter.
This time instead of a tool used for cutting a material, there are multiple small nozzles that pick up electrical components using a vacuum. The machine then moves to a desired location and places that electrical component down on the printed circuit board (hence the name pick and place).
Pick and place machines move very quickly and are used to place the many hundreds or even thousands of electrical components that make up devices such as computer motherboards, phones / tablets, and pretty much everything else that has a printed circuit board.
5 Axis CNC Machines
5 axis CNC machines add two rotary axes to the typical three axis setup.
The rotary axes allow much more complex machining to produce parts that would be impractical/impossible to do on a “normal” CNC router or mill.