What is G92 used for in G-code

Question

On the reprap wiki it says using Znnn it sets a new axis position.  But then it says "No physical motion will occur". What would the line G92 E0 be used for?

Mick · Accepted Answer

The G92 command is used to set the start position (origin) of one of more axes (including the current extruder) to any arbitrary value. The command G92 E0 is often used to perform retraction and nozzle priming. For example, the following commands are often used in start-gcode sequences (prologues) to prime the current extruder by extruding a small amount of filament:

G92 E0     ; Reset the extruder's origin
G1 F200 E3 ; Extrude 3 millimetres of filament
G92 E0     ; Reset the extruder's origin

RepRap Wiki: G92: Set Position

Davo · Answer

To supplement the accepted answer, and answer a question in the answer's comments (which should not be there), consider the E value as another axis - the axis of the filament.
If you executed:
G92 E0     ; Reset the extruder's origin
G1 F200 E3 ; Extrude 3 millimetres of filament at a rate of 200 units per second

and then went on to printing, the first filament move would have to take you from E3 to whatever E value the next move specified.
If the next move assumed starting at E0, you'd already be 3 mm further along, and the first move would probably be a retract, so for example, if the next printing move was:
G1 Xnnn Ynnn E0.5 ; Extrude 0.5 millimetres of filament

then instead of extruding 0.5 mm, you would actually retract 2.5 mm, to get from 3.0 to 0.5. Just like moving in a negative direction on any other axis.

What is G92 used for in G-code

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