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I-J arcs

I J arcs refers to a method of programing G02 and G03 words without using the R word (radius). To program the arc below with the R word it would take two lines of code. Example clockwise arc from PT 1 to PT 2
N100 G02 X8 Y3 R6
N110 G02 X0 Y-3 R6

The IJ arc is a single line of code that describes where the center of the arc is relative (incremental) to the beginning of the arc. It uses the "I" word to describe the horizontal increment to the center of the arc and the "J" word to describe the vertical increment to the center of the arc. Example clockwise arc from PT 1 to PT 2

N100 G02 X0 Y-3 I6 J0 (where X and Y are the absolute coordinates of the ending point of the arc)

R word arcs used today would not work on the NC machines of the 1970's because of the slight pause while the slow controllers read and acted upon the next block of code. This would create a witness mark. Controllers are much faster today and there is virtually no pause between blocks of code.

See also circular interpolation