Reviewing some of my Gcode, I see the phrase “Restore absolute mode”. Where do I find an explanation of absolute mode? How does this relate to the Machine Position and the Workpiece Position?
It’s a change in the way the move commands are to be interpreted by the machine;
In absolute mode (G90) the actual destination coordinate is expected, for example, if the machine was currently located at X10 and you wanted to move an additional 20 to the right you would send ‘X30’.
From the same X10 starting location, in incremental mode (G91) you just send ‘X20’ to move to the same exact place.
The G90 mode is like giving somebody an address to go to, the G91 is relative, so more like “I don’t care where you are right now…just move to your right 20 paces”
Machine position is based on the machine origin X0Y0, which is determined by where the machine is when it turns on, or as part of the homing function of the machine.
Workpiece positions are like bookmarks in a large book, they conveniently shift the X0Y0 origin to make it easier to program your project, and to move your project around different areas of the CNC. For example, If I was a cabinet maker I might program the drilling coordinates for a draw runner, x0, x40, x80 and run it at position(A) and then reuse the same program somewhere else at position(B) just by redefining the work offset.
MillMage expects you to define a Workpiece zero and tells the machine to remember that position relative to your machine coordinates using the G54 offset.
For example, when you zero the workpiece Millmage sends something like “G10 L20 P1 X0Y0Z0” to ask the machine to remember that location.
In the simple program below Millmage tells the machine to first apply the G54 offset to shift this program to where it needs to be, and then runs it in G90 mode, but in this same location this program could just as easily be re-defined as G91 relative gcode.
G00 G17 G40 G21;Restore metric mode
G54
G90;Restore absolute mode
G0 X10Y10
G1 X30F6000
G1 Y30
G1 X10
G1 Y10
G90;Restore absolute mode
M2
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Absolute (G90) means every X or Y move is referenced to the Home position or Origin.
Incremental (G91) means every move is referenced to the current position of the laser.
- You are at X100 Y100
- Absolute G01 X50 Y50 moves you back to X50 Y50
- Incremental G01 X50 Y50 moves you to X150 Y150. To get to X50 Y50, you need to issue X-50 Y-50 to move back.
Use ABSOLUTE. It eliminates a lot of confusion. It is making the MillMage workspace and machine positions agree, like one is over top the other.
You can play with User Origin and Current Position when you have no deadlined to meet.