Continuing the discussion from Sunday Meetup 26th April at the Welshmill Hub:
I think perhaps it was @Palee00 who had that trouble. @qscons has found some information:
I have a possible answer to the gentleman who came in last month to discuss his 3D printer filament “snapping” backwards. I think I have seen something similar on my Ender 3. Even if it’s not the cause of the problem it is something that’s worth checking. A 3D printer may over-(or under-) extrude, for example if the gear wheel that grips the filament is replaced by one slightly bigger. Under certain circumstances the extruded PLA has nowhere to go, and compression stress builds up in the filament in the Bowden tube, eventually causing the filament to “snap” back. The check and fix isn’t difficult - you CALIBRATE the extrusion. You instruct the 3D printer to extrude (say) 10cm of filament and measure how much it actually extrudes. You can then change the stepping motor steps/mm value accordingly. This is worth doing anyway - I’ve fixed under-extrusion problems this way.
See this video which @qscons found:
