Filament extruding problem

Hi,

I've had a Fisher for a while now and it's been printing fine. recently, however, I've had an odd filament extrusion problem. If the filament is extruding and is then retracted it then jams one a subsequent extrusion. This happens at the start of a print usually, so if I can get it started then its fine, but sometimes it just jams when printing the outline/perimeter. I've taken the effector off and run the hot end up and manually pushed filament through and it's really easy to extrude, but a retraction and re-extrusion causes a jam more often than not. I think what is happening is that the filament is cooling and hardening on retraction and jamming, but I can't see how this can happen as the hot end is...hot.
Also, once it has jammed it's damn difficult to pull the filament out again which also points to a cooled filament somehow.

Anyone else seen this?

Andrew

Yes, I have had something similar. In my case, the filament to stuck to the nozzle tube above the hot zone. If that part is not smooth enough, the filament can stick firmly to it, leading to a blocked nozzle. As you mentioned, some force is needed to pull it loose, but after that it seems fine.
My solution was to polish the inside with the shank of a 2mm drill and some scouring soap (CIF) and a polishing paste afterwards. You will need to disassemble the hotend from the heatsink, not too hard to do.

[edit: clarified 2mm drill]

Edited 1 time(s). Last edit at 11/24/2015 11:53AM by Jelle.

Interesting. By 'nozzle tube' do you mean the bowden tube, or the top part of the hot end steel nozzle part?

Andrew

The stainless steel nozzle+tube part, not the bowden cable.