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gareee

How to properly adjust retraction on the UM2+??

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I want to increase retraction of the printer to try to correct issues. What exactly do length and speed do?

(Does length mean the distance it calculates before retraction, or the amount of retraction it pulls?)

I'm not sure if I should be increasing the numbers or decreasing them.

(I'm getting some stringing and occasional thread fingers sticking out.)

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If you look here you can see 3 values. If you have very small differences between two towers for example between which the stringing appears you should decrease the first number. It decides from when it does the retraction.

If you print a very little amount between the different parts you should decrease the second number. for example when you print very thin features. Then lastly you have the z hop which will move your build plate down you it retracts. This should be increased if you want it to have more effect.

Could you add a picture of your build than i could help you with the settings.

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Grab the bowden gently at the feeder and lift. Repeat at the print head. If it isn't tight - if it slides in and out - then fix that first. If that is fixed in place then 4.5mm is just about perfect for retraction distance. The faster the better for the retraction speed because that means less time sitting there oozing while retracting. Even more important you can get good results possibly by increasing the extruder acceleration but if you are going to do that you need to get out a micrometer or ruler and remove the bowden and use repetier host to move the filament 100mm at a time up and down with different accelerations until you find where it loses steps.

More likely the fix for your stringing is to lower the temperature.

https://ultimaker.com/en/community/2872-some-calibration-photographs

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The bowden is tight at both ends. I'm already running hatchbox filament temp pretty low.. its rating is 180-210, it seems to print best at 184, and if I leave the printer on its default 210 it actually liquefies and drips out!

Something else thats been bothering me, is when the head travels across infill or edges, sometimes it seems to hit slightly. (Not causing print issues, but I'd think that it would be travelling up above that.)

I don't get the stringing with matterhacker pro and get it slightly with the um silver included with the printer.

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Some filaments still seem to string no matter how cool you go.  I put those filaments in a special box and only use them for certain flat parts such as my quadcopter frame which is completely flat and has almost zero retractions.  These filaments also tend not to do overhangs - even mild overhangs very well.  They tend to be very thin/liquidy (not very viscous) at normal printing temperatures and I lower the temp to 180C and they still drip.

So I'm guessing you have one of those filaments.

If the print head is hitting edges - that is common and more is discussed here:

http://umforum.ultimaker.com/index.php?/topic/4094-raised-edges/

Skip right to "page 2" and look at foehnstrum's video and read all the posts after that possibly.  It's not until around post #39 and later that we really begin to understand what causes the issue.

The problem has to do with the fact that liquid PLA is stretchy like melted mozzarella cheese or like mucus. The liquid plastic is pulling like a rubber band as it goes down and creates a lip or raised edge where there is an overhang. The effect gets stronger on each succeeding layer. It is what causes the lower quality "look" of overhangs. Sometimes the part will actually rip free from the bed because of this (which is easily fixed by making parts stick like hell - another topic).

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