Numerical Control Programming
Chapter 2
How Does Numerical Control Work?


It is necessary, if one is to become an expert N/C programmer, to have a thorough understanding of how the N/C system operates and what it is capable of doing. However it is not necessary to be an electronics engineer or understand the electronic circuitry of the computer chips in the controller. Complex machinery such as N/C and CNC machines--with all their buttons, switches, knobs, dials, flashing lights, and CRT displays--can be very intimidating. But when one understands what an N/C machine does and how it performs its tasks, the intimidation disappears. It then becomes a relatively easy task to program an N/C machine and put it through its paces.

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What Moves--The Cutter or the Workpiece?

The function of an N/C program is to direct the motion of a cutting tool around a workpiece to generate the desired geometric shape. N/C programs for milling machines must be written as though the workpiece were stationary, except for rotary motion, and the cutting tool did all the moving--right, left, in, out, up, down--even though in fact most N/C milling machines use a stationary cutter (except for rotary and axial motion) and move the workpiece around the cutter. Hence programmers must "lie" to themselves and think in terms of the cutting tool doing all the moving around a stationary workpiece.

It is not necessary to "lie" about N/C lathes. In a lathe, the workpiece rotates, rather than the cutting tool. But the workpiece does not change its location. The cutting tool moves along the rotating workpiece. Hence lathe tool motion commands are written as they in fact occur.

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Next:  Getting Oriented: Axes and Directions

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Updated Jan. 9, 2002
Copyright 1988-2002 by George Stanton and Bill Hemphill
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