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Big blob at end of print, UM2+

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Since a recent upgrade, I now always see each print end with a huge (3x3mm) blob driven into the object with the head remaining in the final position. Apart from the slight mess on the final print, this causes the filament-driving teeth to grind the plastic, so that the NEXT print fails to feed any material until I remove the PLA filament, cut off the ground piece, and re-insert it.


I've printed over 100 hours with this printer, it worked fine until the latest upgrade to fw 2.6.2, and works splendidly in every other respect. I'm using a new install of Cura 3.2.1 on macOS with a UM2+.


Is this a (known) bug in the latest firmware? Should I downgrade? And if so, to which version?




PS. As a quick check, I just printed an object sliced by an earlier version of Cura, and that completed fine. So the problem may actually be in Cura, not the firmware... therefore, attached: an object which prints WITH the extra blob. Hopefully that will help someone diagnose this issue.


Edited by jcw

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Recently this problem was reported in the Cura 3.2 subject forum.

The problem is caused by a change in Cura which exposes a bug in the UM2(+) firmware: At the end of the gcode file, Cura used to save a few lines with the used Cura settings. These settings were removed making the file a few lines shorter and this exposes the bug where the UM2(+) finishes the print while still a few moves are in the motion controller buffer.


The bug will soon be fixed and consists of two changes:

1) We will fix the bug in the UM2(+)  firmware.

2) Cura will make the gcode files a bit longer again so the UM2(+) bug will not occur on older firmware versions.


For now the workaround is to revert to Cura v3.1. Or add about 10 extra comment lines at the end of your gcode file, or add an M400 command at the end of your gcode. These commands can be set in the 'End Gcode' section of your Cura machine settings.


Here a link with more info about the UM2 bug:


Edited by Indy31

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