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Many stone fabrication newbies will be walking through a trade show or attending a seminar and will hear the term CNC. This term is used frequently in our industry. It may not be new to the seasoned fabricators, but the beginner may be a little confused as to what a CNC machine is. In the following article I will present some basic information on CNC technology, including what a CNC machine is, some history of the technology and also some terminology you should know. Even the veteran CNC machine operator may find the following informative.
What Does CNC Mean?
CNC stands for computer numeric control. CNC machinery was introduced in the United States in the 1970s and made its way over to the stone industry a few years later. So, what does computer numeric control mean? Quite simply, a CNC mimics and replaces a certain task in the fabrication process. For example, let's look at edge profiling.
If you're using one of the many routers available, you have to manually attach the bit, adjust the height of the router bit, lock the spindle, adjust the speed, add the proper amount of water and then push and pull the machine along the edge. As you can see, there is a lot of human intervention and that can leave a lot of room for error. This is especially true if the operator is not experienced. The operator will have to perform this task over and over again which can lead to fatigue.
The CNC machine can do those same movements by programming the movements and operations into the machine. In other words, it will do everything automatically. Think of CNC technology as nothing more than a robot that repeats the same tasks over and over again.
How Does A CNC Work?
The movements of a CNC machine are simple but the programming, mechanical and electrical components are complex and need to be engineered so that all these elements will work together. I won't bore you with all the technology, but will explain in basic terms how the CNC machine works. In other words, how does it know to go to a certain position, pick up a tool, run in one direction, etc?
If you remember your basic geometry classes, you should know what the x and y axes are. In case you don't, let me explain. The x, y and z axes are called directions of motion — in other words, right and left, up and down for the x and y axis. The z axis is a little more difficult to explain but basically it is the near and away from you.
The x axis is the horizontal direction going both right and left. The y axis is the vertical line. Any motion going to the right and horizontally of the y axis is positive and any motion to the left horizontally of the y axis is negative. Any motion going up on the y axis above the x axis is positive. Any motion going down below the x axis is negative. If this were a 3-D diagram, the z axis would be coming straight out of the page or through the other side of the page. Imagine you are holding this page up and you push a pencil through the page. The line direction of the pencil would be the z axis.
The x, y and z axes are all linear or along a straight line, and the bed of the CNC machine is nothing more than a big graph that the stone lays on.
Now, when you hear someone talking about a 3-axis CNC machine you should know what they are talking about. But, what the heck is a 4-, 5- or 6-axis CNC machine? OK, you asked for it. The x, y and z are all linear axes; however, there are also rotary axes motions commonly named A, B and C.
CNC Machine Programming
Programming a CNC machine requires a lot of computer experience, but fortunately one can learn to operate a machine with some good training. In other words, you don't have to be a computer nerd to operate one. Program it, maybe, but not to operate it. Let's take a look at how basic programming works.
A CNC machine will move only when it is told to move and where to move. Because of this, a set of instructions is needed to tell the spindle of the machine where to go, how fast to go, etc. This language uses a code or words to communicate with the machine's brain. There are only about 50 common words that tell a CNC what to do; for example, "S" would indicate spindle speed. Keep in mind that the language and programming are very complex and I am not trying to make light of this subject. This is just a basic explanation to help you understand the basics of how the machines work.
CNC Controller
The CNC controller takes the instructions (or code), interprets it and executes the commands. It does nothing more than what it is told (programmed) to do. Today, controllers are complex and can also perform other tasks. For example, you can program the controller to do a dry run, etc.
Hopefully the above has given you a better understanding of how a CNC machine works. For further reading on buying a CNC, see The Stone Shop column that appeared in Surface Fabrication magazine's May 2007 issue, "Is A CNC In Your Future?"
About the author:
Fred Hueston is a worldwide expert on stone installation, failures, fabrication and restoration. He is the founder of The National Training Center for Stone & Masonry Trades (ntc-stone.com) and Stone University (stoneuniversity.org). He can be reached at Fhueston@aol.com.
author: By Fredrick M. Hueston