CNC stands for computer numerical controlled machining, and milling is a process that is similar to both drilling and cutting. However, in the case of CNC milling, tools move on multiple axes, with the work piece moved in different directions. On a traditional machine, the cutting or drilling occurs along only one axis, with the machinist controlling the movement of the materials through the machine. The axes on a CNC milling machine are as follows:
- Axes X and Y represent the horizontal movement of the work piece being machined, moving it either forward or back or from side to side.
- Axis W designates the diagonal movement of the work piece in a vertical movement.
- Axis Z represents a vertical movement within the work area.
Instead of a machinist standing at the machine directing movement of the work piece, the milling machinist takes a blueprint of the item to be made and figures out from the specifications the approach needed to produce the desired object. The machinist will then program the directions for the CNC mill to produce the object.
CNC machines can mill any material—silicone plastics, wood, stainless steel and nonferrous metals—and are able to produce a wide range of components of varying complexity with consistent, high-quality results. From jewelry, to aircraft parts, to medical implants, many of the products in our modern life come to us through CNC machining.
The Origins of CNC
The first CNC machines—or NC machines as they did not require a computer back then—were built in the 1950s. The United States Army bought 120 NC machines and loaned them to various manufacturers who had contracted to make parts in an efficient, consistent, cost-saving manner. As the manufacturers ran the machines and became more familiar with them, NC began to catch on in the early 1960s.
As you can imagine, those early machines, much like the early computers ENIAC and UNIVAC, were huge and slow compared to today’s standards. Modern CNC machines are much faster, more accurate, safer, and highly reliable. They can range from a desktop model for around $3,000 with a target audience of the serious hobbyist, to a six-position industrial machine costing as much as $50,000 or more.
The accuracy of modern CNC machines is such that once they are programmed with the design, they can be operated 24 hours a day; they only need to be switched off for maintenance. In addition, one person, the machinist or engineer, can supervise many CNC machines at once, thus saving on staffing. While CNC machines are more expensive than manually operated and staffed machines, the ability to manufacture products over three shifts without needing to schedule three staff shifts returns more value on the purchase of the CNC machine than of a manual mill. The CNC machinist/engineer can also create “virtual prototypes” by using computer aided design before committing to creating a prototype on the CNC, sometimes at considerable cost savings.