FANUC G72.1/G72.2 figure copying: why L4 does not mean 4 additional copies beyond the original
The 0i-F machining-center figure-copying rules explain why the nth transformation uses n−1. Original linear and three-way rotational arrays calculate first and last positions, with the first subprogram block and inter-contour connections treated as separate constraints.
Contents
An array can have correct spacing yet contain one extra part if L is interpreted offline as the number of copies added beyond the original. In the FANUC figure-copying function cited here, call 1 is already included in L.
First establish where the copy count begins
The 0i-F machining-center manual B-64604EN-2/01, §5.8, pages 174–177 (public mirror of the original manual, pagination of this copy) lists figure copying as an optional function: G72.1 provides rotational copying and G72.2 linear copying. The nth angular displacement is R×(n−1), and translation is the programmed shift ×(n−1). The G72.1 rotation center is interpreted as an absolute position even in incremental mode.
A linear array: calculate the first instance, then the last
Original XY-plane example: an identifiable endpoint of the base contour is S=(12,8) mm, copy displacement d=(35,−6) mm, and L=4. Only geometric positions are calculated; no actual machine program is specified. Endpoint n is Sₙ=S+(n−1)d.
| Call index n | Displacement from the base contour, mm | Corresponding endpoint Sₙ, mm |
|---|---|---|
| 1 | (0,0) | (12,8) |
| 2 | (35,−6) | (47,2) |
| 3 | (70,−12) | (82,−4) |
| 4 | (105,−18) | (117,−10) |
The first instance is not shifted by one spacing in advance, and the fourth is only three spacings away. If the base contour was machined separately before calling the copy function, instance 1 of the following L4 may repeat that location. Examine the program structure to establish whether the existing instance was already intended to belong to the array.
A rotational array also includes the zero-angle instance
With the origin as center, R=120°, L=3 and base endpoint (20,0) mm, the three angles are 0°, 120° and 240°. The results are (20,0), (−10,10√3) and (−10,−10√3) mm. Changing to L4 incorrectly adds a fourth instance at 360°, returning the endpoint to its base position rather than creating a fourth distinct three-way position.
Correct geometry still leaves connecting moves to check
This edition requires the first block of the copying subprogram to contain motion, and the first move to be absolute. A mismatch between one instance's endpoint and the next instance's start produces a connecting move. The copying subprogram must not change the selected plane or the coordinate codes listed in that section, including G54–G59. These requirements appear on the cited pages 175–177; ordinary M98 call intuition is not a substitute.
Offline validation should display both every contour and the moves connecting them. Checking only the four endpoint coordinates can miss connecting paths across fixtures or machined contours. Increasing L does not replace withdrawal and clearance planning. See the OPTION section for related coordinate transformations.