CNC

Description

"CNC stands for “Computer Numerically Controlled”. The terminology was previously just “NC” because for 60 years or more, some machine tools in factories have been Numerically (digitally) Controlled by paper tapes with punched holes or magnetic tapes. As the tape was passed through the machine’s reader, rows of holes representing numbers gave the tool’s motors instructions on where to move the cutting head to cut or machine material. The tapes were programmed by engineers or technicians using a scheme called “G-code” which was designed to cram as much information as possible onto the tape. The tape process seems a little primitive today, but it does indicate that the technology for providing a tool with sequential digital instructions for work to do goes back a long way. The recent addition of “Computer” as the first “C” in CNC reflects replacing the punched tape with a computer in order to provide the tool with instructions more directly. The addition of computers makes NC tools considerably more powerful and flexible, and helps make them easier to use. " (http://www.shopbottools.com/cncdefinition.htm)

Example

Shopbot Tools at http://www.shopbottools.com/cncdefinition.htm

Discussion

1. Steve Richfield, Apr 27, 2010 at 12:30 at the singularity@v2.listbox.com :

"REALLY ADVANCED CNC (Continuous Numerical Control) manufacturing machinery, some of which exists today, is instantly reconfigurable to make many very different things. Just put CNC into eBay and see some of what you can now buy on the used market. This march toward ultimately flexible manufacturing machinery is clearly headed toward a manufacturing facility that can efficiently manufacture just about ANYTHING, and do it a LOT cheaper than robots ever could. Of course, these are just another form of robot, able to take files directly from CAD (Computer Aided Design) programs and directly turn them into the desired physical objects.

To understand where this is heading, you must first understand the operation of a modern Screw Machine. In these, several, typically 6-8 chucks hold pieces of material that are being machined to a particular shape, In one kerchunk, an equal number of tools are applied to the chucks, but each tool performs a different operation, and the tools are retracted. The chucks then rotate one position, while dropping a finished part into a bin and loading a new piece of unmachined material into a chuck. In short, you can stand there and watch a screw machine going chunk, chunk, chunk and see finished parts emerging at the one-per-chunk rate. No robot could ever operate a lathe to function at anything approaching such a rate.

There are other machines that can make ANYTHING from tubing, make ANYTHING from sheet metal, etc. Put an assortment of these machines in one large building, and nothing but another such building can compete.

China is now moving in this general direction, buying up the machinery in shut-down American plants. Once this transition is complete, ALL manufacturing will be done in city block sized manufacturing facilities and NOT in anyone's garage, nor with anyone's robots."

2. Dianna Pfeiffer:

"All other digital fabrication is accomplished with CNC or CNC-like tools. Traditionally, these have been computer-automated machine tools that use coded operations and processes for precise tool control and require the running of a set of programmed commands for each part fabricated. Less formally, CNC is considered as any tool-like process that is a computer-controlled series of operations and movements.

Much more configurable and diverse than RP&M, CNC tools may in fact be materially subtractive, additive or otherwise manipulative. Subtractive CNC tools used in design and making are multiaxis milling, routing, and turning machines, laser cutters, sign cutters, hot-wire foam cutters, plasma cutters, and water jet cutters. Additive and manipulative CNC tools include benders, sewing machines, welding machines, and robotic arms capable of multi-axis movement with various tool attachments.

All types of digital fabrication require that the digital geometry is appropriate to the tool and is adequately communicated to it. For CNC, the creation, manipulation, and conversion of digital information are accomplished with a combination of CAD/CAM software (Computer Aided Design /Computer Aided Manufacturing). For standard machining processes such as milling, turning, drilling, etc., CAM software is used to generate a set of coded operations and processes from CADcreated geometry. These commands are then output to the tool via a programming language, often g-code or related language that precisely describes tool paths, feed rates, and stock material placement.

Solid free-form fabrication and the CNC-like tools (e.g. laser cutters) are different, however, in that they usually incorporate the CAM operations directly into their functioning. Acting more like desktop text printers, they automatically convert the sent data into a particular output with little user control over the method." (http://scholar.lib.vt.edu/theses/available/etd-12152009-131820/unrestricted/Pfeiffer_DV_T_2009.pdf)