Can anyone identify this issue? - loops of filament on corners

I'm getting what I can best describe as occasional filaments that don't follow the correct path when the nozzle changes direction, I often see them around the perimeter of holes, but it does seem to be whenever the head changes direction (but only occasionally, not all the time).

I printed the small cog from a Wades extruder this evening (see attached photo) which I think shows the problem reasonably well. This was printed in PLA at 0.3mm layer height (the whole cog is 21mm high), using Slic3r, and Marlin firmware (my printer is a DIY i3, box frame, with RAMPS).

Edited 1 time(s). Last edit at 12/10/2014 05:11PM by plankton.

If it's on change of direction, your belts might be a bit loose. It also looks like you're over-extruding a little.

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I think I may be onto something.

I've only ever seen it on >= 90 degree direction changes, but it seemed too random for the majority of mechanical causes. So I wondered if it could be due to temperature (the filament not being flexible enough to keep up with the nozzle on sharp direction changes), I just tried another print increasing extrusion temperature by 5 degrees and this time there are much fewer artefacts. I'll do some more testing at different temperatures tomorrow, but I think I'm on the right track.

I've been printing so far at 190 first layer and 185 subsequent layers, it seemed to work so I didn't bother to try different temps until now, and I've never seen this mentioned as a symptom of low temperatures before.