random retracting with Octoprint

[peterk]

My Rostock V2 has been happily printing through Octoprint in the last month. There is one little issue that drives me up the wall but while I haven't solved it I found "something".

I use Repetier Host firmware on the printer, create the gcode files on Ubuntu version of Repetier Host and upload them to Octoprint. Sometimes I have noticed that the prints start but for a few seconds no filament comes out of the nozzle even though it's being pulled in from the spool. Sometimes it doesn't affect a print but often it does. For a while I suspected some problem in the gcode files coming out of curaengine but couldn't see anything.

But I just noticed today that, as the printhead dives towards the platform, the filament feeder (or whatever you call it) runs backwards at high speed. Of course at the time the extruder wants plastic it will have to wait until the filament has caught up in the other direction - dry run for a few seconds. Again, I looked in the gcode files but there is no retraction happening. But then I noticed that when I use the "Extrude" button on the control page of Octoprint to make sure filament is flowing and the extruder is ready to print, the printer will somehow retract filament the same distance right before getting to work. I haven't seen that mysterious retracting when I don't to a test extrusion.

So, question then: Which component "remembers" the test extrusion and asks for retraction? Is it the firmware in the printer? Seems like there might be a gcode command that would essentially reset the printer. Or a setting in Octoprint?

[Xenocrates]

The problem is absolute extrusion. Add a G92 E0 to your start G code, or better yet, configure your slicer (and printer), for relative extrusion.

[peterk]

G92 E0 did the trick. Thanks!