I printed engraved letters but found many brownish burnt marks and unwanted strands. Then the nozzle temperature is reduced from 190oC to 180oC. The brownish burnt had disappeared. The strands reduced as well but still existed. I use CURA. As there other parameter can improve the print out?
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You need to increase the retraction of the filament when the extruder is moving from one point to another without extruding to prevent stringing like that.
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Thanks for your advice. I had increased Retraction -> Distance from 3mm to 4.5mm but the result had no difference. CURA help suggested to 4.5mm only. Should I further increase it?
it depends how runny your filament is when the nozzle is hot, you should check it when the extruder is just moving (and not extruding) and there should not be any filament coming out of the nozzle then that’s the right retraction value. is the cooling fan at it’s max speed? it should be. and set the outline speed to 15mm/s or less.
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Xeno
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Maybe " Z-hop on retraction" could help
Shahramorobotics, Thanks for your advice. I tried Retraction-> Speed 15mm/s & Distance 8mm. The print out is much better.
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Does Z-hop work in XYZ machine? Cura Help advises it lift the nozzle for Delta Tower and suggests to 0.075mm? I tried Z hop = 0.1mm but it had not much difference.
Looks like it gets worse when it’s printing that last layers. Have you tried to put an external fan next to your print?
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What is the purpose of an external fan? We always try to maintain high ambient temperature in printing, even though it is PLA, but an external fan cools the print out.
PLA is not like ABS and won’t warp if you cool it while printing. The thing is that when the nozzle gets to those last layers it quickly stacks up the layers that are not yet cold enough to print the next layer on top of them. It’s like printing a cone, the higher you go the faster each layer finishes and every new layer is being printed on a hotter layer than before. If you print two cones next to each other then the same stringing like yours happens. Is your nozzle a flat head or thin?
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Now I understand your point. Cura have no control to the fan speed in different layers. Should I place a small fan on the hot bed at the print-out tip elevation to have localise cooling?
The nozzle is thin type.
That should do it. I usually use a portable fan at low speed to circulate the air in my printing room pointing directly to the printer and not so close.
Also the nozzle looks good for your model, have you tried a steel nozzle? it doesn’t get hot like brass nozzle and when it’s moving on layers has way less stringing.
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Wow, I just ordered a brass 0.2mm nozzle to try any improvement on stringing. Perhaps I will order a stainless steel one in the next month. You clear my question of the function of a stainless steel nozzle. I asked many guys but no one can give an answer.
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Yeah, steel nozzle is not good for ABS or high temp filaments because it doesn’t get hot like brass but for PLA it works really well. 
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