I stand corrected. In my zeroing codes that are generated by the Triquetra Tool Box I include G91 for at the beginning of all my moves to insure that they are incremental and not absolute. It makes a major difference in how the machine interprets the commands and responds.
To clarify for those that don’t understand:
Two common movement types that come into play when zeroing are G90 and G91.
G90 sets your machine to Absolute mode. This means that your machine will move to a defined set of coordinates.
G91 sets your machine to Incremental Mode also know as Relative Mode. This means that your machine moves in increments relative to its current position.
Lets assume that your bit is currently located at coordinates X10 Y10 and Z1
Lets also assume that your machine is in G91 (Incremental) mode and you are moving in Inch Mode.
If you send the command
G0 X1.000 your bit will move 1 inch to the right. So now your would be at coordinates X11 Y10 Z1.
If your machine was in G90 (Absolute) Mode and you issued the same command
G0 X1.00 your machine would move to coordinates X1. Now your machine would be located at coordinates X1 Y10 Z1
To avoid problems that arise when you are using both G90 and G91 moves in gcode files it is good idea to include those commands at the beginning of each line of code. In the below code I want to move from X10 Y10 Z1 to X Y Z zero. A easy way to accomplish this is to send the absolute movement:
G90 G0 X0 Y0 Z0 This command will move all three axis at the same time until they reach zero.
You could also send the move in Incremental mode using G91 instead:
G91 G0 X-10 Y-10 Z-1 Your machine would respond the same either way, however, the G90 move is a better choice because it doesn’t matter where you start if you know exactly where you want to stop such as X Y Z zero.