CNC Repair Tip #17: G30 Position (2nd Reference Position) on Fanuc Controls
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What is a G30 position?
CNC repair work often requires that you have an understanding of how the G30 works. In short, it’s a 2nd reference position…or 3rd reference position…or 4th. It is a position set in NC parameters that is a specified distance from the machine zero-return position. It may be used to set a tool-change or a pallet change position that is not machine zero.
I say 2nd, 3rd or 4th, is because setting parameters allows you to have several “alternate” reference posoitions. On Fanuc 16, 16i18, 18i,21, 21i, 30i, 31i and others, NC parameter 1241=2nd reference, 1242=3rd reference, 1243=4th reference.
As stated, on Fanuc 16, 16i18, 18i,21, 21i, 30i, 31i and others, the G30 position is set in parameter 1241 for the specified axis. Other controls will use a different parameter number (see Commonly Altered Parameter Chart).
Let’s say that you have a horizontal machine that has a headstock that moves in X and Y and the table feed toward the spindle is Z axis. Let’s also say that the position at which the ATC functions is not machine position X0.0000 and Y 0.0000. X and Y have to move to a G30 position for the ATC function. Calling the 2nd reference poistion in a program for the X and Y axes of a machine with a Fanuc control would typically look like this: G0 G91 G30 X0. Y0.;
It breaks down like this:
G0: RAPID MOVEMENT
G91: INCREMENTAL DISTANCE
G30: 2ND REFERENCE POSITION
X0.:DISTANCE FROM 2ND REFERENCE POSITION
Y0.:DISTANCE FROM 2ND REFERENCE POSITION
The machine will move in rapid to the values set in NC parameter 1241 (on specific controls) for X and Y axes from machine zero for these axes.
Calling up the 3rd reference position in a program for the X and Y axes of a machine with a Fanuc control will typically look like this:
G0 G91 G30 P3 X0. Y0.;
It works the same way as the 2nd reference position call but the “P3” calls the 3rd reference position specifically. The machine will move in rapid to the values set in NC parameter 1242 (on specific controls) for X and Y axes from machine zero for these axes.
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Tagged With 2nd reference, apc position, atc position, fanuc, Fanuc CNC, Fanuc Control, fanuc controls, g30, machine zero, second reference, zero position