In CNC programming, fixture offsets are used to define the position and orientation of the workpiece relative to the machine coordinate system. Fixture offsets allow the programmer to write the program in terms of the part geometry, without worrying about the actual location of the part on the machine table.

The most common fixture offset is G54, which is also the default offset. However, sometimes it is necessary or convenient to use more than one fixture offset for different operations or parts. For example, if you have multiple identical parts on the same fixture, or if you need to change the orientation of the part for a different operation.

This is where G54.1 comes in handy. G54.1 is a command that allows the programmer to use up to 48 additional fixture offsets, numbered from P1 to P48. These offsets are stored in the CNC memory and can be accessed by using the G54.1 command followed by the offset number.

Usage format

The usage format of G54.1 is as follows:

G54.1 Pn

where n is the offset number from 1 to 48.

For example, to use the offset number 5, you would write:

G54.1 P5

To return to the default offset G54, you would write:

G54

Explanation

The additional fixture offsets are defined and set in the same way as the default offset G54. You can use the jog mode, the touch probe, or the manual data input (MDI) mode to set the offsets. The only difference is that you need to specify the offset number after the G54.1 command.

For example, to set the offset number 5 using the jog mode, you would do the following steps:

• Move the tool to the desired position and orientation of the part zero point.
• Press the OFFSET key and select the WORK OFFSET screen.
• Press the G54.1 soft key and enter 5 in the P field.
• Press the PART ZERO SET key and select the axes that you want to set.

The offset number 5 is now set and stored in the CNC memory. You can use the same procedure to set the other offset numbers as well.

To use the offset number 5 in the program, you would write:

G54.1 P5

before the program block that requires this offset. The CNC will then use the offset number 5 to calculate the tool position and movement. To switch to another offset, you would write:

G54.1 Pn

where n is the other offset number. To switch back to the default offset G54, you would write:

G54

Example

Here is an example of a CNC program that uses G54.1 to machine four identical parts on the same fixture. The parts are arranged in a 2×2 grid, and each part has a different offset number. The program uses G54.1 to switch between the offsets for each part.

O1000 (Program number and name) G90 G94 G17 (Absolute, feed per minute, XY plane) G20 (Inch units) T1 M06 (Tool change to tool 1) S1000 M03 (Spindle speed and direction) G54.1 P1 (Select offset number 1) G00 X1.0 Y1.0 (Rapid to first position) G43 H1 Z0.1 M08 (Tool length compensation and coolant on) G01 Z-0.5 F5.0 (Feed to cutting depth) X2.0 Y2.0 F10.0 (Cut a square) X1.0 Y2.0 X1.0 Y1.0 G00 Z0.1 (Retract) G54.1 P2 (Select offset number 2) G00 X3.0 Y1.0 (Rapid to second position) G01 Z-0.5 F5.0 (Feed to cutting depth) X4.0 Y2.0 F10.0 (Cut a square) X3.0 Y2.0 X3.0 Y1.0 G00 Z0.1 (Retract) G54.1 P3 (Select offset number 3) G00 X1.0 Y3.0 (Rapid to third position) G01 Z-0.5 F5.0 (Feed to cutting depth) X2.0 Y4.0 F10.0 (Cut a square) X1.0 Y4.0 X1.0 Y3.0 G00 Z0.1 (Retract) G54.1 P4 (Select offset number 4) G00 X3.0 Y3.0 (Rapid to fourth position) G01 Z-0.5 F5.0 (Feed to cutting depth) X4.0 Y4.0 F10.0 (Cut a square) X3.0 Y4.0 X3.0 Y3.0 G00 Z0.1 (Retract) G54 (Select default offset) G00 X0 Y0 (Rapid to home position) G49 M09 (Cancel tool length compensation and coolant off) M05 (Spindle stop) M30 (End of program)

The text diagram below shows the arrangement of the parts and the offsets on the fixture:

+-----+-----+
| P3  | P4  |
|     |     |
|  +--+--+  |
|  |  |  |  |
+--+--+--+--+
|  |  |  |  |
|  +--+--+  |
|     |     |
| P1  | P2  |
+-----+-----+