Clogged nozzle

[printbus]

Have you already tried to remove the filament from the extruder, cut off the end and re-feed it? There's a lot of things that can cause the filament to stop extruding, with the nozzle not being clogged. Examples -

• Bulges in the filament that get caught at the top of the hot end (my *favorite*; dark filaments are prone to do this)
• Excessive spring pressure on the guidler causing deep cuts in the filament that causes it to catch on the hot end (I haven't seen this, but I've read about it and it makes sense, but I don't recall anyone proving spring pressure was a direct cause of extrusion problems)
• The filament spool not rotating freely enough (multiple people have seen this happen with the stock spool mount)
• Overzealous retraction leading to the hobbed bolt rotating back and forth over the same length of filament, carving away at it
• Too low of a nozzle temperature (leading to the hobbed bolt having to apply a lot of pressure to force the extrusion)
• Too fast of a print speed (hot end can't keep up with the flow volume)
• hobbed bolt teeth contaminated with filament shavings or other material
• filament shavings falling onto the top of the hot end where they migrate into the feed tube of the hot end, increasing resistance to filament movement (makes sense, but also unproven)
• combinations of the above
• filament actually only fed down to the top of the hot end, and not actually into the tube of the hot end (1.75mm filament in the 3mm-capable wades base is real prone to this)
• trying to use a soft or flexible filament in the wades extruder that has a large gap between hobbed bolt and top of the hot end

EDIT: I've probably had the extrusion stop over a hundred times, and only once or twice has it been due to an issue with the nozzle. Of course, I do pass the filament through a felt pad at the top of the extruder to wipe off the plethora of cat and dog fur in my work area. (see the white spot above the extruder in my avatar - that's the felt disk) That could be wiping off dust and who knows what else from the filament that could end up forming a clog.