Gee Two Eight: Return To Home Position
G28 Commands the machine to move to the reference home position. However it’s a bit more complicated than it may appear at first viewing. It is always “Incremental command” ie: the move is relative FROM the existing position rather than TO a defined position as such with the option of controlling which axis moves first and by how much. It’s pretty easy to get wrong and cause a bang so play carefully. This means you must either use G91 to set incremental mode OR U & W rather than X & Z
Syntax:
G91 G28 X0.0 Z0.0 this will cause the machine to move at rapid speed to the reference HOME position moving BOTH axis in the shortest direct way possible. This may well be straight through the side of your workpiece or with one of the other tools in the turret hitting some part of your fixture or workpiece.
G28 U0.0 W0.0 This will do the exact same thing as above. U is the incremental name for X and W is the incremental name for Z.
Note: When substituting U & W for X & Z in a move command the move will be INCREMENTAL so no G91 command is needed.
The preferred method on a 2 axis lathe is as follows. (Green notes are NOTES not part of the program) This avoids the issue of putting the machine into “Incremental mode” and forgetting you have done so. Consider your syntax carefully so you move each axis while considering what it *could crash into on the way home.
- G28 U0.0 (Move X axis to home position)
- G28 W0.0 (Move Z axis to home position)
There are other methods that can introduce mid points for each axis on it’s way to home but that’s for later when this little lot has been digested.
G28 Is A Non-Modal Command