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albert

Messy first layers - no retraction

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Hi everyone,

I lately keep running into problems with larger models that have holes in them. On the first layer, the printer first traces the outer perimeter, then goes to the inside and traces the holes, but without retraction, so I get a lot of messy thin PLA tracks that will either not stick to the bed at all or they will melt and mess up the printhead when the head returns to the second round.

On a particular model I have restarted the print for an hour until I got it to do the first layer. I even tried to modify the model to start the holes a couple of tenths after the first layer and then drill them out.

I have tried several versions of CURA, even going back to 13.03 with Skeinforge. I think there should be a short stop, retraction, then going in for the inner perimeters of the holes...anyone had the same problem?

 

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Hi Daid,

thanks for getting back to me..I will try to get some photos but it may take a while since I'm out this afternoon.

BTW: you have helped me this summer to get CURA running on my two older machines. I'm happy to report that all your later versions run perfectly on my machines now.

 

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I think the issue may be that when doing the skirts, there is no retraction used. More recent Cura's draw a skirt not only around the convex outside of the shape, but also inside any internal holes in the first layer, if there is room. When moving between those, there's no retraction used, so an extra bead of plastic usually gets dragged across what will then become the base layer of the print.

 

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I wondered myself whether this is a bug or a feature?

Imho this really sucks. The inside skirt makes no sense at all but always messes up the first layer.

Using retraction for the first layer however might be problematic. I imagine that the filament wouldn't stick well after having been taken off the platform for retraction and put back.

However if there were no inside skirt, there would already be considerably less of a mess on the first layer. I guess we have to live with what's left, usually it wasn't too bad until recently when the inside skirt came.

Oh, and also I think the inside brim is more a pain than a help because if you have small holes (like for M3 screws) they will be completely covered up and you have to search for them and pry the brim out.

I would suggest solving the problem with introducing a rule for inside skirt / brim: Use an inside skirt / brim only if the surface area of the "hole" is greater than X mm2.

Ideally, put "X" into the expert settings and set it to 0 by default.

I don't find a better word for the "hole": I mean the inside opening of the part where there's going to be a skirt / brim.

 

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It does already do retraction when moving between islands of actual print on the first layer, and it works fine - so doing that for the skirt/brim as well shouldn't be that big of a problem. But then I never really have first layer problems anyway. I print by UM1 first layers at 75mm/s, and my UM2 at 40 - although I could probably do the UM2 quite a bit faster now everything is settled in.

 

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Hi again,

Thanks for all the replies, I have uploaded a few pictures to the gallery. Unfortunately I have forgotten how to embed them right in here....

The problem is not the skirt, it is the inner perimeters. The head does a fast travel move to get to the start point of the inner hole and leaves a messy line of pla behind. This empties out the nozzle and so the start point of the inner circle wont stick.

The remedy for this would be to either " print" the travel move or to retract - stop and re- prime the nozzle for the next step.

I have tried various bed levels, speeds and temperatures but could not get this to work....

can I change some other settings in Cura to get rid of this problem?

edit by gr5: added the images (next time click "my media" when you are want to insert the pic):

image

image

 

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Oh then that's just the general case of Cura not being as careful as it might be on top and bottom surfaces. You can make it retract by turning off combing in expert settings, and setting the minimum travel distance to something small, like 1mm, and the minimal extrusion to 0.

That should make the extruder retract for most every move, and so reduce the problem.

 

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I've recently started to use Cura (on my MendelMax 1.5), and have the same issue as Albert.

I guess I could try @ illuminarti 's solution, but it sounds like a significant overhead and may add far more retractions in the main body of the print.

I've not tested this, but is it just the skirt that doesnt retract or is it anything on the first layer?

I gues one alternative if its not everything on the first layer where retraction doesnt work, would be to turn off skirts and add some custom GCode e.g. via a plugin, that drew a few lines near the side of the print bed to effectively prime the printer which I think is basically what skirt is doing now ??

Thanks

Roger

 

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Skirt/Brim doesn't retract no matter what.

The interior parts of the first layer (or any other) won't retract unless you turn off 'enable combing'. Arguably you don't want the nozzle oozing on long internal moves anyway as it will cause under extrusion on the perimeters afterwards. So I'm not sure that turning it off is ever a bad idea - if you set the minimum travel and minimal extrusion according to your print's needs, then you really won't be any worse off.

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So... It seems in Cura 14.01 there has been a lot of improvement done with brim.

Small holes don't get brim anymore, and medium holes don't get closed all the way by the brim anymore. I like that very much, good work Daid!

However... (darn :???:) I frequently have problems with small holes (typically M3 holes for screws) on the bottom layer. The small circles usually don't stick well and get dragged around, messing up the entire first layer (and rendering the part useless or at least ugly in the process).

I'm currently working around that by not drawing these holes all the way through the part, but leaving 0.1mm of material on the bottom. This makes the bottom flat and gets me a clean first layer. The holes then start on the seond layer where they print fine.

The workaround has some annoying parts to it however:

For one, it means that I always have to use the same first layer height. If I ever choose to make my first layers thinner, I'll have to redesign every single hole in all of my parts...

And then there is the thing that if I do that with a design that I publish on YM, then I have to explain about that and everyone else will also have to use the same first layer height (or have stronger material to cut away when post-processing the part).

So, I want to propose another feature for Cura:

Make it possible to ignore all inside "islands" on the first layer, so that it will always print a clean and simple first layer and start with the inside structures on the second layer. Cutting that away afterwards is no problem, and the first layer looks much better because there aren't strings everywhere.

Maybe make it like that:

"Print inside structures on bottom layer only if larger than: XX mm2".

Default: 0 -> will always print everything. So, no change unless someone wants it.

That would pretty much solve every issue with the first layer!

/edit:

Some images to illustrate what I mean:

clean first layer

First layer is clean. Easy to print without any issues.

 

second layer

Second layer starts the inside strutures. These print nicely and without problems on top of the first layer.

Post processing is easy as there is only one layer that needs to be cut away. The result is still far better than normal.

Note that some filaments melt up very well on a HBP and that all the mess won't be visible anymore. But that is not always the case! Especially with my good, preferred PLA filament it is definetly NOT the case.

 

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@JonnyBischof

Isn't your request basically what the Platform Adhesion - Raft function do ?

You can set the Raft height in the expert settings to the height of your layers, so you'd only get one layer of Raft

Personally, I think its still a pain to have to remove the raft and punch out a load of small holes and makes things messy.

It would be better if Cura does what Slic3r does and only puts an outside perimeter / skirt.

BTW one other thing you can try is setting the skirt spacing to be quite large e.g 20 mm, I think I did some tests and this worked some of the time, but I don't think it was a usable solution all of the time.

 

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I have never really looked into the raft feature. From what pitures I've seen, I remember raft as some ugly and wide net printed under the actual part.

Tried it in Cura quickly (don't have much time - I'm just on a quick break) and I actually almost got the result I wanted. It's just a pity that you can't seem to combine it with a brim (which is necessary too or the part will warp).

The problem seems to be that the raft consists of two layers. Setting one layer height to 0 removes the extra margin (brim).

I'll have a large disc grinder soon, maybe I'll do tests with regular rafts that I can just grind away afterwards...

I would still appreciate the feature as I suggested above - using a raft seems more like a workaround than a real solution to me, even if you can configure it to do just the same thing it is not really intuitive.

Also, if it is independent of any platform adhesion type, then you can easily switch between using or not using brim, but still having no trouble with internal structures.

@gr5:

I do have a little issue with levelling atm: one corner is just a little bit too low (maybe 0.5mm or less) and can't be any higher. I'd have to add a washer, but I'm going to redesign the entire z-stage soon, and I don't usually have problems. The rest is levelled pretty good, you can see it very well with a polished glass (or stone in my case) plate.

/edit2:

I've printed multiple small and large parts using my workaround so far, and they all came out very good. I had a tiny bit of warped corners here and there, but only like a few mm2 areas and less than 1mm high...

 

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This problem is still existing today in Cura 3.2.1 - please could you enable retraction in first layer or slice so you don't move the head around so much. The setting says:

image.png.bfd8485f6fc2a466fc6c737eecad9b71.png

The print bed IS a "non-printed" area so it should retract. Right now first layers are ruined (ugly lines on the surface) at the moment due to this. The slicer does not show stray lines

ScreenShot338.thumb.png.8912d1dc8d54a03d717fb55082df3e99.png

but the real world does

5a8d315614075_2018-02-2109_38_04.thumb.jpg.48756a241c966fcf629d759420f3bbdf.jpg

Edited by hoegge
added picture showing explanation of the retraction setting

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I second the motion. :-) I see this all the time and have varied between living with it and heroically diving in with tweezers. Printing on a glass bed, that's typically my best surface of the print and I have to ruin it with these little dribbles.

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@hoegge & @AbeFM has anyone of you managed somehow to prevent those ugly lines in the first layer with some 'special' settings?

Maybe someone could write or has already written a small plugin for this, I'm new to 3D printing and GCODE, but I think it should be that hard to create a small plugin for that.

 

 

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On 2/21/2018 at 3:45 AM, hoegge said:

The slicer does not show stray lines

 

but the real world does

I think you have to check the box that shows moves (in blue).  I like to keep that one checked.

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1 hour ago, mat89 said:

has anyone of you managed somehow to prevent those ugly lines in the first layer with some 'special' settings?

If you disable combing for the bottom layer (type comb in the search terms just above the profile settings) then it will greatly improve the quality - those lines will mostly disappear.  Not all of them but most of them.  The difference is that if combing is disabled then it will retract every time it moves from one part of the print to another.

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combing mode: no skin

 

This disables combing on top and bottom layers - layers that are visible but keeps it enabled for internal layers.

 

Like I said above - type "comb" in the search box - this will show you settings that are hidden as well.  The search box is just above all the settings and just below the profile drop down.

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