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dennis-van-roeyen

How to get rid these artifacts ? (picture included)

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Well, so "printing direction" means... "Z direction".

I'm not sure why did you make this choice of positioning the part (looks like part of an enclosure with ventilation holes, but is just an impression). The point here is that the piece seems to be longer in the "print direction", which makes it somehow fragile.

This being said, the area between the holes is perhaps 5 mm or so. 50 mm/s is too much for such short perimeters. At the corners, the nozzle will drag the extrusion a bit in the new direction so that it will not be laid straight. Additional to the advice in the post above, just try to increase fan speed.

 

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Well, so "printing direction" means... "Z direction".

I'm not sure why did you make this choice of positioning the part (looks like part of an enclosure with ventilation holes, but is just an impression). The point here is that the piece seems to be longer in the "print direction", which makes it somehow fragile.

This being said, the area between the holes is perhaps 5 mm or so. 50 mm/s is too much for such short perimeters. At the corners, the nozzle will drag the extrusion a bit in the new direction so that it will not be laid straight. Additional to the advice in the post above, just try to increase fan speed.

Yes, Z-direction.

It's indeed an enclosure with ventilation holes. It's printed this way because any other direction would have more overhangs. The area between the holes is about 7mm.

I now redesigned the ventilation holes to not have these small islands. But it's good to know that slower printing and increased fan speed might help.

thanks!

 

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.25mm layers is fine but definitely slow it down if you want higher quality. Why?

These artifacts are caused by the printer speeding up and slowing down the extruder. The extruder speeds up and slows down because X/Y speeds up and slows down. XY movement has to slow down on corners because it has a maximum jerk/acceleration setting.

The "jerk" setting isn't "true jerk". Instead, in Marlin, jerk is defined as the magnitude of the instantaneous velocity change at a vertice. Max jerk on ultimakers is 20mm/sec. So for example if making a 90 degree corner the *change* in velocity can be as high as 20mm/sec so it comes into one corner at 14mm/sec and leaves going 14mm/sec the other direction (14^2 + 14^2 = 20^2). So if you keep the velocity closer to the jerk setting (20mm/sec) the extruder won't have to slow down and speed up and you get smooth perfect extrusions.

Every time you slow down you get some over extrusion because the nozzle has too much pressure. Every time you speed up you get under extrusion because it takes time to build the pressure back up in the nozzle. That's the "artifacts" you see in your picture.

 

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I like very much the picture since it clearly shows patterns of artifacts, depending on "holes structure".

Now, thinking about what George wrote above, that's clear that the actual print direction, meaning for me the direction the head is moving to lay down the extrusion, is in our case from left to right :)

Then, going from bottom to top, one can see very clear the effect of the phenomenon that George explained particularly on the left edge of the first part of the first hole to the right :) And is not so bad yet. As long as another hole enters the picture, the situation is getting worse. With 2 is still reasonable, but when it gets to 3, ough! Here is where mainly lack of fan let things go badly. Apparently speed has not so much a contribution, because in a few mm of acceleration you will not get to a terrible speed, but that's enough to "ring". This is visible where the holes are far apart, elsewhere heat is partially... melting the evidence ;)

 

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