CNC stands for "computer numerical control." A CNC machine is simply a machine whose movement is controlled by a computer. A CNC router is a machine that can route, mill, surface, drill, groove, saw and polish depending on the model and manufacturer. Each operation needs only a different tool and those tools' operating parameters. Most CNC machines available today offer an "automatic tool changer" whereby the machine can change the tool by itself without manual intervention. That means if you type "T1" into the control, the machine will return whichever tool it is currently holding to its own tool position before going to pick up Tool #1. How many tool positions a machine has varies by vendor and model. For instance, the Brembana Maxima can have a 22-, 26-, or 44-position tool rack.
Programming for these machines is accomplished using software, and each year the software gets better and easier to use. Most CNC machines that use industrial controls have had flexibility and reliability designed into them, but driving the machines with little or no software can be at best trying. In a recent development, CMS Brembana is working with a technology company to use digital imaging in place of manual templating, which means, instead of making a physical template, one can just take a series of digital photos in the field, and the CNC programs can be made from this data using only software.
The practicality of CNC technology within the fabricating shop can be effectively illustrated with a "Time Study" for an inclined drain-board with an undermount sink cutout. An inclined drain-board is a feature that is becoming more and more popular with designers and architects, but is very difficult to fabricate manually. The "Time Study" calls out which tools are necessary to machine a certain piece and the time it takes to complete each operation.
Inclined drain-boardThe following are working time calculations for a kitchen countertop inclined drain-board. The machine to be used in the study was a Brembana (Maxima, Speed 3 or Junior). These are actual, realistic working times, which could be reduced further by speeding up these processes, but this may compromise the quality of the finish. This example is a 1,000 mm x 500 mm drain-board with a basin cut out of 320 mm x 460 mm and two holes. The drain-board was machined and polished at a .3 deg inclination and has a 60 deg bevel around its perimeter. The sink cutout was fabricated with a semi-bullnose edge for an undermount sink. The material was 3-cm-thick Africa Black granite.
In just over one and a half hours, the fabrication was complete, with a polished drain-board and sink cutout ready to mount the bowl and install.
A CNC machine is an impressive tool. It can, and should, become the most important machine in a fabrication plant. When considering the purchase of a machine, there are four important elements to look for. Look at the structure of the machine. It should be well built and strong, and a buyer should beware of anything that is bolted. The CNC control should be a hardened industrial control that has worldwide technical support. The spindle should be the largest you can find. Lastly, the service and after-sales support is without a doubt the most important issue.