Printing...tool paths, slicer issue?

[uze6666 1]

Hi, I have noticed some of my prints sometimes appears to print some of the tool paths on some layers (using Cura 4.03). Although not so critical in my case, it's sad to see those scars on an otherwise smooth surface. I'm using a UM2, ColorFabb PLA @ 210deg, .100mm layers@ 125mm/s. Since that material is wasted there, I get some under extrusion in other parts of the model.

But today it actual build up a "wall" of tool path! What is going on? Is this a bug in Cura or the printer (UM2)? Any ideas what's could cause this? I've read a bit and will try Cura 14.04RC1 to see if it still does the same thing.

 

[gr5 2,266]

You need to enable retraction.

If retraction is on those blue lines will have a vertical line at the start to indicate it is a retracting move instead of just a non-extruding move.

Also in addition slowing down the print speed (to reduce pressure in the nozzle) and/or lower the temperature often helps.

Also for that bottom layer if you *disable* combing it will typically force it to retract for that non-extruding move also and reduce that "scar". That may have changed in a recent version of Cura though.

 

[uze6666 1]

Retraction is actually on and I can see vertical blue lines in Cura. Here's the setting used, anyone see's something tyo correct under the retraction section?

If will try printing at lower temp and speed and disable combing to see how it improves.

Thanks!

 

[dreamworker 1]

I have the same problem on flat surfaces with retraction on, like you.

 

[Dim3nsioneer 558]

Retraction is actually on and I can see vertical blue lines in Cura. Here's the setting used, anyone see's something tyo correct under the retraction section?

If will try printing at lower temp and speed and disable combing to see how it improves.

Thanks!

you might try if disabling combing makes a difference. But probably it won't.

Something else you can test is to increase the filament diameter setting. Best thing would be - if not done yet -to measure it at ten different spots and then take the smallest value. From that point on iteratively increase the diameter by 0.01mm and see how it works.

Lowering the print temperature might also work.

[conz 0]

I have observed the same behaviour. Single lines on the clean, nice surface made by these pathes/movement.

Retraction is on. But it seems, that cura is not adding a retraction command before these pathes. (I have not looked in the gcode). I got some material on the infill, too, on these movements. It looks really like there is some extrusion of material at the time of the movement. (Looks like a bug)

Maybe as a workaround there could be an option for lifting the head on pathes over finished surfaces (if it's on the same layer)

Sometimes the path could be more optimized to take the shortest line over a finished surface.

EDIT:

Some sample image with material over infill. Seems the same problem.

It doesn't look like smearing, it looks like added material on the movement to the new printing position.

EDIT2: Combing and retraction are on for this print.

 

[Dim3nsioneer 558]

I don't think there's a bug. The effect is quite well known. If you have combing enabled, there is not retraction and the hotend is oozing during the travel which creates the lines on horizontal surfaces. If the the travel distance is large enough the loss of material can even lead to underextrusion afterwards as e.g. illuminarti has pointed out many times here in the forum.

The recepy to avoid the effect is:

- disable combing

- low temperature decreases oozing

- fast travel speed minimizes the material loss

- the retract hop feature further minimizes the effect

- keep your nozzle clean (also on the outside)

 

Sometimes the path could be more optimized to take the shortest line over a finished surface.

 

I remember Daid having written in a post that everybody who is able to program a better combing algorithm than the existing one is highly welcome to contribute it to Cura.

Finally, the RetractWhileCombing plugin allows to 'disable' combing and provoke retraction for certain print heights/layer numbers. The plugin also includes the hop feature ('lifting' the head).

 

[conz 0]

Thank you Dim3nsioneer, I have to test disabling combing and the plugin.

... the plugin ... where can I find the plugins for cura?

 

[Dim3nsioneer 558]

... the plugin ... where can I find the plugins for cura?

 

Here: http://wiki.ultimaker.com/Category:CuraPlugin

 

[uze6666 1]

Thanks Dim3nsioneer for the plugin, I'll give it a spin too. I don't care if the slicer doesn't retract inside the infill or in invisible parts, but if at least I can force it to do so a couple layers before the surface, that's good enough for me! :smile:

 

[gr5 2,266]

Getting back to the original poster. Since you have retraction happening then the best solutions are to speed up travel moves. 150mm/sec is the minimum recommended speed. 300mm/sec should be fine (it's more the acceleration that is difficult - not so much the speed so 300mm/sec should be fine).

Also lower temperature. Here are some tests I did with stringing and temperature (see very first post, very first picture):

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

 

[uze6666 1]

Made another print yesterday. All in all, I'm very happy and impressed by what the UM2 is capable! You can still see those scars on the surface, they are everywhere. It's kinda of a shame considering the rest is so awesome. I printed at .1mm layers, 50mm/s, 150mm/s travel @ 219 deg on UM PLA. Though I forgot to use Dim3nsioneer 's plugin. I'll do more tests with the ideas mentioned by you guys.

 

[uze6666 1]

I did a test print of the last few milimeters with the same params but combing disabled. Indeed all but one scars are gone. Though it seems to introduce other artifacts.

I'll try another one, a 210 deg, 300mm/s travel, Z hop at 0.075mm. Btw why not have Z hop on all the time? Also, what is the bad side of disabling combing altogether? Too much retraction will damage the filament or something?

Oh, one more, you guys think it's possible to have better surface finish on the UM2, perhaps with specific brands of filament?

 

[profepaco 0]

is the same question I am asking here:

http://umforum.ultimaker.com/index.php?/topic/5646-top-and-bottom-layers/

 

[uze6666 1]

Alright, I tried printing at 210, but the filament feeder would start to skip, so I brought it back to 220. UM Blue PLA, 50mm/s print, 250mm/s travel, Z hop at 0.075mm with combing on and using the retract while combing plugin for the last few layers. Problem solved, no more scars or other artifacts! You can see some in the middle part, but that's ok, they are in layers before the plugin kicked-in and it will be covered by a cover plate anyway. Thanks for the tips gr5 and Dim3nsioneer! :-P

 

[Dim3nsioneer 558]

Be aware that any Cura plugin can be used more than once in a print. With the RetractWhileCombing plugin, you could specify two single layers, some layers apart, by setting start and end layer number the same for each time.

 

[conz 0]

Why is there this hardwired connection between retraction and combing? Couldn't be this a seperated option to activate / deactivate the retraction with combing on?

Why would I activate it on a specific layer and not for the whole print?

 

[Daid 306]

Why is there this hardwired connection between retraction and combing? Couldn't be this a seperated option to activate / deactivate the retraction with combing on?

 

IMHO, when combing (staying inside the print area) no retraction is needed, as any oozing that will happen will end up inside the print and be invisible. With combing it still retracts when moving outside the print object boundary.

 

[conz 0]

IMHO, when combing (staying inside the print area) no retraction is needed, as any oozing that will happen will end up inside the print and be invisible. With combing it still retracts when moving outside the print object boundary.

 

IMHO, it will make a difference.

- It is some added material that is not intended, and there is always some oozing.

-- It will take some layers to even out the additional lines/material. Sometimes you can see these lines on the finished surface from the layer below.

-- It seems that the combing algo isn't aware of a finished surface (EDIT: on the same layer). A finished surface could be marked as outside the print area.

- If I have a lot of plates on different hight, than it would be anoying to activate / deactivate the "Retract while combing" (with the plugin) for every plate.

 

[gr5 2,266]

There is some kind of "hop on move" setting or something where it moves the Z up - does that make a difference?

 

[illuminarti 18]

Z-moves are very slow, compared to x-y, on non-delta printers like the UM, so you can introduce other issues such as blobbing in place during the lift. But there may still be good use cases for z-lift.

I agree with Conz, and we've also shown several times on here that the oozing that happens during combing moves can impact the finished surface quality by leaving the head under-pressure when the time comes to start printing the perimeters. The decision to retract or not should be independent of the one about combing.