I am new to gcode and I am using reprap wiki as a resource to learn it. However, even after I read the definition of M82 and M83, which is set extruder to absolute or relative mode, I still don’t quite understand what it really means. Can someone explain it to me? Any help would be highly appreciated!

Absolute coordinates are determined from a “0” point or the “beginning or starting” point and all future positions/coordinates are based off that first point where as a relative coordinate is derived from the current position. So, for relative, the next position or coordinate is based off of the current position or coordinate.

If you are in absolute mode and you give the command to extrude 5mm, it will extrude 5mm. Then if you give it a command to extrude 2mm, it will retract 3mm so that only 2mm of material is extruded. In relative mode, 5mm will extrude 5mm, then 2mm extrude another 2mm, for a total of 7mm extruded.

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Thank for your reply! It makes sense now. I think that the relative mode it more straightforward. I am curious at what situation would you use the absolute mode? If it retracts 3mm in your example, then what will be the difference from setting a retraction?

Thanks for your reply! I really appreciate it.

I haven’t had to mess around with gcode too much with my machine, but I guess if you wanted to customize your starting/ending/tool-change code you would have to be aware of the differences between the two modes and use the appropriate one for the situation. (I use Simplify3D as my slicer, not sure if other slicers use the same terminology)

It is simple.

Say, you are currently in the HOME position (x=0, y=0, z=0) and you are about to run

G1 X100 Y100 Z10

Will lead you to (X=100, Y=100, Z=10), regardless you are in absolute or relative mode.

However, after that, another

G1 X100 Y100 Z10

will lead you to (X=200,Y=200,Z=20) if you are in relative mode, but will not move at all if you are in absolute mode.