The CNC Process (Design: Programm Generate: Machining)

A modern-day CNC works by someone beginning with a design in a Computer Aided Design (CAD) software package. When the design is complete it is transferred to a Computer Aided Machining (CAM) software package. At this point the operator chooses exactly what will be cut, what speeds and depths will be used while cutting and in what order will everything be done.
When this is complete the CAM software will generate a G-Code file. This G-Code file contains a list of commands and coordinates which specify everything the CNC machine needs to know in order to produce the movements which will create the design.

The G-Code file is loaded into a CNC Controller software package. This CNC Controller speaks directly through the computer to the CNC electronics. It is the controllers job to decode the G-Code file and turn the desired movements into electrical signals which will drive the CNC electronics.
The CNC Controller is also responsible for knowing the CNC machines limits as defined by the operator. It will make sure that at all times all movement is within the specified limits. This is a major part in the CNC process, it keeps the operator safe and the machine safe from destroying itself.
When the electrical signals reach the CNC electronics it is delivered to a breakout board. This breakout board protects the computer by isolating the signals before sending them off to the drive electronics. The drive electronics are responsible for driving the actuators which move the CNC machine around. These actuators may be stepper or servo motors, depending on the machine.

The drives then move the motors as commanded by the received signals. This process will happen many thousand times per second as it will take many millions of small electrical signals to complete every movement required to produce the designed part.

Cartesian coordinate system

Cartesian coordinate system is used in CNC to numerically assign direction and plane of movement. A Cartesian coordinate system is made up of reference lines called a coordinate axis, or just axis. These axes are all measured in the same unit of length (for CNC it would be inches or millimeters).
This coordinate system allows CNC machines to be controlled along each plane of movement. It is at the very heart of CNC technology and you will need to understand it well in order to be able to operate and program CNC machines.

By now you would have seen X, Y and Z coordinates mentioned everywhere. They refer to the planes, or axes of movement of a CNC machine. In simple terms they mean:

X axis = Left and Right movement
Y axis = Forward and Backward movement
Z axis = Up and Down vertical movement

We now have 3 referenced axes in 3 dimensional space. This means our CNC machines can now cut 2 dimensional profiles and cut them at different depths using the Z (vertical) axis. This movement suits the majority of CNC router, milling, laser, plasma and 3D printer machines.

However some may want more advanced movement than this; such as the ability to rotate around these axes. This is where A, B and C come in:

A axis = Rotation around the X axis
B axis = Rotation around the Y axis
C axis = Rotation around the Z axis

These new axes allow us to not only move within our 3 dimensional space but to also rotate along any axis. This gives an almost unlimited ability to work anywhere within a 3D space, however we will always be limited by how our CNC machine grips or holds the material and various other size constrictions imposed by the size and design of the CNC machine.
CNC machines with these rotational axes are often refered to as 4th axis, 5 axis or 6 axis machines. You may also come across terminology such as a 5 axis BC head or table. This refers to the head or table of the CNC machine being able to rotate along the B and C axes.
These additional axes are usually seen on much higher end, more expensive CNC machines. The addition of rotation on axes increases the difficulty of G-Code programming immensely aswell and usually requires specialised CAM software.

The Different Types of CNC Machines

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 Machine

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 new very high accuracy ball screws and various new mounts built for mounting the actuators to the machine.

Lathe

Just like the milling machine, lathes are also commonly retrofitted with CNC technology in the exact same way.

 Machines that are Custom Built for CNC Operation

 Router

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 have no human interface other than through the computer.

Routers are generally for producing larger work and more commonly built with the idea of cutting wood, plastics and sheet metal in mind. Router also are most commonly found in a 3 axis setup (X, Y and Z). This set up will allow cutting of basic profiles and 3 dimensional relief machining. There are also CNC router which are 4, 5 or even 6 axis, these machines are more suited towards cutting more complex shapes or prototype models.

Milling Machine

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 can be absolutely massive and have built in tool changers, auto-feed mechanisms for loading in material and various electrical sensors for safe monitored cutting.

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. However laser cutters use a much less destructive force than a plasma torch – A laser. Laser cutters are often good for cutting wood, plastic and metal. Each will need a different strength of laser suited for the material.

3D Printer

A 3D printer or 3 Dimensional printer uses a similar set up as a CNC router or laser cutter, except it uses a plastic extruder. This plastic extruder pushes out hot plastic through a tiny hole and slowly, layer by layer deposits enough plastic to build up a completed part.

Pick and Place Machine

A pick and place machine again uses a similar set up as a CNC router or laser cutter. This time there a multiple small nozzles, that pick up electrical components and then move into a desired location and place that electrical component down. Hence the name pick and place!

Pick and place machines move very quickly and are used to place the many hundreds or 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.

WHAT DOES CNC MEAN ?

CNC means Computer Numerical Control. This means a computer converts the design produced by Computer Aided Design software (CAD), into numbers. The numbers can be considered to be the coordinates of a graph and they control the movement of the cutter. In this way the computer controls the cutting and shaping of the material.

What is CNC Technology

The first numerical control (NC) technology was developed by John T. Parsons in 1947 while mating a milling machine to an IBM punch card system.  It wasn’t until the early 1950’s that engineers from MIT added the first ‘real’ computer element to the machines and forever changed how the new CNC machines operated.  CNC was an important advancement for machines to consistently reproduce complex machining steps without human intervention.
CNC (Computer Numerically Controlled) always refers to how a machine controls its basic method of movement. A CNC machine will read a long list of digital coded information from a computer to move the motors and other positioning systems in order to guide a spindle over the raw material the machine is working on.
A CNC machine uses mathematics and coordinate systems to understand and process information about what to move inside the machine, where to move it to, and how fast to move it. Most CNC machines are able to move in three controlled directions at once on its axes.  The axes are given simple names such as X, Y and Z with the X always being the longest distance a part of the machine must travel.  The Y and Z axes will move from left to right and vertical to complete the job. Each CNC machine operates and positions itself with the use of spindles.
A CNC machine has to communicate with the computer to function properly. A computer numeric control unit sends position commands to the motors. The motors then must communicate back to the control unit that it has acted correctly and moved the machine a given distance. The ability of CNC machines to move in three (or more) directions at once allows the machine to create almost any desired pattern or shape.  Oetlinger Precision Manufacturing Company (OPMC) has state of the art equipment and each operator is fully trained on their respective machines.
The advantages of CNC machining are tremendous as no human could possibly control the precise movements that these machines will make over and over again. One skilled operator can perform the duties of several people thus reducing labor costs as well as part costs.  Each skilled operator will enter the coded data into the machine by hand or with the use of an electronic file system and once the data is entered the quality of the part relies on the quality of the machine.
The wide range of industries that use CNC variants are Heavy Equipment, Drilling, EDM’s, Lathes, Milling machine, Wood Routers, Sheet Metal Plants, Wire Bending Machines, Hot Wire Foam Cutters, Plasma cutting, Water Jet Cutters, Laser Cutters, Oxy Fuel, Surface Grinders, Cylindrical Grinders, 3D Printing, and many more.

HOW THE COORDINATES WORK

The way coordinates are used can be seen opposite. The X, Y and Z axis control the movement of the cutter on a 3D CNC machine. This allows materials to be machined in three directions (3D manufacture).