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This print failed a couple of hours in. I was wondering if the nature of the print surface, with lots of retracts (similarly the previous print which was OK) might have contributed to the clog, or if it's just bad luck? To be clear, the surface has lots of short dead-end, not just a wiggly perimeter. enter image description here The filament seemed to have stopped moving, and was cut through by the drive gear.

This was a genuine Titan Aero extruder, 0.4mm nozzle, 215C (on an Anet a8 printer)

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Reading your question it's not clear to me if you are referring to filament retraction (which is a configurable setting) or surface recesses which seems what you are referring to when writing:

the nature of the print surface, with lots of retracts

If it is the latter, then the answer is "no". The amount of complexity of the surface of the model does not correlate directly to the possibility of the printer head clogging.

If it is the former, then the answer is "possibly". It is in fact not so much the amount of retracts that affects the likelihood of a clog but rather their speed and lenght. If you retract too quickly and too much filament, you risk to have molten plastic being "sucked" into the cold end, solidify, and act as a glue, blocking the filament in place.

This is especially true for all-metal print heads like titan aero, as plastic sticks a lot better to metal than to PTFE.

However, with a properly calibrated retraction, you shouldn't experience problems regardless of how many times / how often you retract the filament.

In general, it is a common misconception that retraction should work as a plunger, actively sucking in plastic that would otherwise ooze out of the nozzle. However all you need is to just release the pressure within the melting chamber, and in a direct drive (i.e.: non-bowden) extruder, this requires a very minimal retraction.

Finally: what material are you printing in? The picture shows a lot of oozing for being PLA. If you are using a flexible material like nylon or ninjaflex, you should probably just let retraction alone: the hysteresis in such materials is very high, and retraction often does not work predictably. If it is PLA, I would try to increase the movement and retraction speed, and probably lower the temperature 10 or 15 degrees. As for the retraction lenght, I don't own a titan, but I would expect the correct amount to be somewhere between 0.5mm and 2mm.

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  • $\begingroup$ Retract is 1.8mm, and yes, I did increase it from 0.8 because of stringing. Temperature may be the clue. $\endgroup$ Mar 3 '18 at 16:57
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In addition to the retraction distance, in the case of this model, I was seeing some places where there were a lot of very close retractions. I think these were increasing the risk of damaged filament, so I reduced the 'maximum retraction count' which at 50 over a 5mm length seemed fairly high.

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