CNC PROGRAMMING CODES Machinery's Handbook, 31st Edition
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G02
R
CW
Start point Start point
R
CCW
G03 Fig. 7. Circular Interpolation.
Fig. 8. Circular Interpolation in Planes. It is very important to understand that the G18 mathematical plane does not correspond to the machine axes orientation and that the arc direction appears to be incorrect. Programming an arc requires a direction of motion in the plane (G02 = CW, G03 = CCW), a start point (typically the current block), an end point (typically the target point, the end of motion), as well as the arc radius. The arc radius can be specified directly (for example R1.5), or it can be defined by special vectors, using IJK addresses. When using direct radius R, there are some limitations. Radius R (positive) can only be programmed for arcs up to and including 180 degree arc sweep angle. If the sweep angle exceeds 180 degrees but is less than 360 degrees, R- (negative) must be used. For a full circle (360 degrees arc sweep angle), the address R cannot be used at all and a two-vector combination must be used. There is no need to break arc motion at the quadrants. The definition of IJK vectors is the same for all three axes, where X and I, Y and J, Z and K are related (paired): The I-J-K vector is the distance and direction from the start point of the arc to the arc center, measured along X-Y-Z axis respectively. A typical milling application in the XY plane is shown in Fig. 9. Current plane selection determines the arc vectors. Some controls use I-J-K as an absolute location. The start point of the arc is defined as the endpoint of the previous motion.
Start point
Start point
J-
R
R
J-
Center
I0 Center
G02
G03
I
Y
X
Fig. 9. Arc Vectors. Helical and Other Interpolation Methods.— Most milling controls offer another mo- tion—helical interpolation (either as a standard feature or as an option), but only very few specialized controls offer parabolic or hyperbolic interpolation. Helical interpola- tion produces a helix. Two axes (typically XY) form the circle while the third axis (typi- cally Z-axis) provides synchronized linear motion. The selected plane (G17, G18, or G19) determines the circular axes, while the remaining axis is linear motion. Helical interpo- lation is most commonly used for thread milling—a method of thread development that offers many advantages over tapping.
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