Problem with strange "pillars" caused by retraction

[jofleck 0]

Hi

A few days ago I bought an Ultimaker 2 and Im very happy with it. As you can see in the picture, I have a little problem. Everytime when I print a model with free spaces and retraction is used, I get these ugly pillars. They are easy to remove but then the surface isn't smooth. I tried to play around with my retraction settings but it didn´t solve my problem. I increased the retraction speed and lengths to 5,5mm and 45mm/s. Also I tried to set the minimal filament and retraction distance in Cura (15.04.2) to zero. I saw my last chance in using z-hop (0.2mm) but it changed nothing :(.

Im using Innofil3D PLA at 210°C and 50mm/s with a layer size of 0.08mm.

Do you have any ideas to get smooth surfaces without these retraction pillars?

[Labern 774]

you can increase travel speed to 250mm/s and or lower temps a bit.

Make sure the bowden is nice and tight and doesn't move during retractions.

check out THIS guide for further advice.

[tommyph1208 55]

You are printing too hot as Labern also mentions... 210 degrees is quite alot for PLA, try somewhere around 185-195 instead...

I also agree on the travel speed, try upping it a bit (250 mm/s should be easily doable on an UM2).

Do you have little locks on the bowden clamps in both ends... Like the blue one in this picture:

Otherwise, just print some and put them on... It will help a great deal with retraction.

Edited October 15, 2015 by Guest

[Labern 774]

you can hold the bowden tight by loosening the 4 thumb screws that hold the head together a bit, the push the tube down and tighten the 4 screws again. this will hold it snug so it wont move.

[gr5 2,178]

I call this "stringing" although this is extremely minor stringing - it's more caused by a tiny bit of PLA on the tip of the nozzle that comes off when it touches the pillar below.

The best solution for this is to try a different brand or color of PLA. Some colors and brands are just worse. Lowering the temperature is the ONLY thing you can do if you don't change PLA. I usually print at 210C - different printers are different as the temp sensors can vary by +/- 20C (usually they are within +/- 5C) so tommy probably has a printer that prints on the hot side but having said that, you might be able to get rid of these pillars at 180C to 190C but if you go that route you need to also print MUCH slower. With layer size of .08mm and temp down at 190C I would stay well under 20mm/sec and at 180C I would stay under 10mm/sec.

Here are typical max speeds for UM2 or UMO - I like to print at half these speeds - these are in mm cubed so you have to take this number and divide by 0.4 (nozzle width) and layer height (.08mm) to get max possible speed on a brand new printer:

[jofleck 0]

Wow thanks for the fast replies.

 

...different printers are different as the temp sensors can vary by +/- 20C (usually they are within +/- 5C)...

I checked the nozzle temp with an IR thermometer. I don't now how accurate it is but at 210°C set on the UM the IR thermometer said something about 230°C and this is definitely too hot. So this evening i will try to print something at 190 set on the UM.

I will let you know about the result

Thank you very much!!!

[gr5 2,178]

The feeder motor shuts off at I believe 170C so you need to keep nozzle temp above that. 180C to be safe or 175C if you are very daring.

[jofleck 0]

Ok at 195°C i get really good results with no or maybe one pillar in the whole print. Below this temperature the quality of the top layers gets bad. But from 210°C to 195°C I can see absolutely no difference between the quality (Except the pillars )

[gr5 2,178]

Below this temperature the quality of the top layers gets bad.

 

That would be due to underextrusion - at this temp the PLA is more like toothpaste (versus honey) and so you need to print much slower - about half the speed you were at or half the layer height. But if you are happy I would stick with those settings. Just be aware that you are "on the edge" of more serious underextrusion so one minor filament tangle may push it over the edge.