Unexpected speed drops during print

On my E3D-BigBox/Rumba with Marlin 1.1.x-bugfix I observed irregular bumps on the outer wall. Looking closer I realised, that at the position of the bumps a very short speed drop occurs which leads to a short over extrusion.

Looking into the gcode (Cura 2.6.2) I found always some points located close together exactly at the position of the bumps.

I edited the gcode by hand and removed the points laying close together and the speed drops and bumps disappeared.

The attached image (Gcode_Plot) shows the points plotted for one outer wall and the printed parts before and after my editing.

Could it be, that a processing limit of the Rumba board is reached if the points laying to close together for a certain print speed?

Edited 2 time(s). Last edit at 07/29/2017 02:17PM by rvator.

Do you print from USB? I had the worst problems with a RUMBA board when printing from USB. The propriatery driver is worse than the ATMega one.

Did you try a different slicer?

I have the issue with both USB (Repetier) and SD card printing. Can't reproduce the behavior with S3D but was unsatisfied with the slicing quality for this application (single wall 3DLabPrint Aircraft) In the meantime I adapted the S3D gcode which was prepaired from 3DLabPrint to my E3D-Bigbox and have good results.