The document discusses CNCMachine Reference Point, which refers to a fixed point inside the CNC machine whose position values are stored. When the CNC machine is turned on, it does not know its current axis position. Performing a CNC Zero Return or Reference Point Return takes the machine axes to the fixed Reference Point, where limit switches signal the reached position and allow the control to update the current position values. The G28 G-code command can be used in Fanuc CNC controls to automatically return all axes to the Reference Point.

1. What is CNCMachine Reference Point?
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You are operating a cnc machine sometimes in auto mode and other times in jog mode. But all
the time the values which a cnc operator sees time to time regularly are the cnc machine current
position.While the cnc machine is running in auto mode the current-axis-position values will
regularly change. And while in jog mode you move cnc machine axis you see the current axis
values are changing.
CNC Zero Return or Reference Point Return
 So these CNC machine current position values are very critical.
 And these current position values are regularly updated if cnc machine axis are moved.
Now you note the current values on a paper, and turn-off the cnc machine. Now turn-on the cnc
machine, now again take the current axis position values, The values have changed,Why?
When your cnc machine is switched-on, it has no provision to know the current axis position.
So at this time the cnc machine needs a way to tell cnc machine control where it is.
So better that we tell the cnc machine where it is now, it is much better to take the cnc machine
axis to a specified and fixed point whose values are known, and now tell cnc machine the current
position.
All the above work is automatically done when we take the cnc machine to reference point or we
zero return the cnc machine.
The reference point is a fixed point inside the cnc machine whose values are already stored in the
cnc machine. So when we take the cnc machine to the reference point those values automatically
get active and the cnc machine comes to know its current axis position.

2. If you want to go more deeper then, there are limit switches for every axis in cnc machine to tell
the reference point position. So when we take the cnc machine to the reference point those limit
switches got active and tell the cnc machine control that the specified axis is reaching to its
reference point position, so the cnc control update the current position for that specific axis
because cnc control already knows the position at that point, and this is repeated with all the cnc
machine axis.

3. Fanuc G28 G Code for CNC Zero Return
You can make a call in MDImode on a cnc machine with fanuc cnc control.
G28 U0 W0
This will automatically take all the cnc machine axis to the Reference Point, or you might say
G28 will automatically zero return the cnc machine.