In the majority of CNC programming applications, there are only two types of tool motions related to contouring. One is the Linear Interpolation. discussed earlier, the other one is the Circular Interpolation, discussed in this post. The programming method of controlling a tool path along an arc is similar to the method of programming a tool path along a line. The method of circular contouring is called circular interpolation. It is commonly used in profiling on CNC vertical and horizontal machining centers, as well as on lathes and many other CNC machines, such as simple milling machines, routers, burners, water jet and laser pro-filers, wire EDM, and others.
Circular interpolation is used for programming applications as outside and inside radii (blend and partial), circular pockets, spherical or conical shapes, radial recesses, grooves, corner breaks, helical cutting, even large counterbores, etc. The CNC unit will interpolate a defined arc with a very high precision, if the necessary information is given in the program.
ELEMENTS OF A CIRCLE
To understand the principles of programming various circular motions, it helps to know something about the basic geometrical entity known as the circle. As an entity that is quite common in everyday life, a circle has various properties that are strictly mathematical, only considered in specialized disciplines, such as Computerized Numerical Control, motion control and automation.
The following definition of a circle and several other definitions that are related to a circle are based on some common dictionary definitions
A circle is defined as a closed curve on a plane, where all points have the same distance from an internal point called the circle center point.
The general understanding of a circle and its various properties as described in this post, provides a sufficient knowledge for general CNC programming. Additional knowledge will be needed for some specialized or complex programming applications. At this time, become at least reasonably familiar with the geometrical and trigonometric relationships for arcs and circles.
♦ Radius and Diameter
In the simplest mathematical terms, a circle is defined by its renter point and its radius. Two of the most important elements of a circle used in part programming are the circle radius and the circle diameter.
The radius of a circle is the line segment from the center point to any point on the circle.
The diameter of a circle is the line segment through the center point of the circle and having both end points on the circle.
The center point location of the circle is also important for CNC programming. The plural form of the word radius is radii, although the word 'radiuses' has been accepted as a colloquial term. In CNC programming, radii and diameters are used all the time, on a daily basis for almost all contouring machines. Drawings used in machine shops use radius and diameter dimensions a lot, with an almost unlimited number of possible applications.
Radii and diameters are also used in relation to the cutting tool Insert designation, they are used for measuring and gauging (inspections), as well as in trigonometric calculations and various auxiliary sketches. In programming, the actual application of an arc or circle is not important, only its mathematical characteristics.
There are two preparatory commands associated with programming an arc direction :
| G02 | Circular motion clockwise CW |
| G03 | Circular motion counterclockwise CCW |
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