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garryhuang

Unwanted stringing

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My UM2 seems to have a habit of dragging filament with it when it's moving from one print area to another, leading to long "threads" connecting the same old places over the duration of the entire print...

See https://www.icloud.com/photostream/#A3GJDfWGG0pYGq

How can I reduce / eliminate this? I have tried printing slower (doesn't really help), I have tried increasing the retraction distance to 5mm instead of 4.5, and retraction speed as well.

What else should I be playing with?

Thanks

Garry

 

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When i get these strings i usually lower the temp (i would go 225 to 220 to 215 now) and lower the speed (maybe 35 -45 mm/s ? ) to keep the same strength in the part. Higher temps usually result in a stronger part and also tends to looks better on vertical walls.

Also as i said, try to play with the travel speed. Try 150 / 180 / 210 and look if its gets better or worse. When i get these strings it looks to me like the pla is sticking to the nozzle. If the nozzle is clean it should stop sticking at the right temperature / viscosity.

 

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260C is dangerous for PLA - if you leave it at the temperature very a few minutes you can caramelize it into gunk that clogs the nozzle. I recommend staying at 240C or lower for PLA. I'm not sure if it's really caramelization - but it seems like it.

To reduce stringing, make sure retraction is truly on. There are about 6 settings and a few of them can disable retraction here and there depending on the situation. So look at it in layer view. In layer view reatractions are indicated symbolically by a vertical blue line.

Faster travel speeds helps break the string - 150mm/sec is the absolute slowest. 300mm/sec should be fine.

Lower printing temperatures helps keep the plastic from leaking out. At 190C it's like toothpaste. At 240C it's like honey. More tests and results here:

http://umforum.ultimaker.com/index.php?/topic/1872-some-calibration-photographs/

But lower temps also means you might have to print slower to avoid underextrusion.

 

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