Adaptive Layers Melting on Top

[splitsecond 0]

hi,

  The adaptive layers functionality almost perfectly solves a problem I had...but not quite.  I am printing a (bald) head figure and so the top is basically like the top of a sphere.

I am printing 0% infill and spiralized so if I don't use adaptive layers the only way the top part of the head will come out as a solid surface would be to print the entire thing at a tiny tiny layer height (there are holes/gaps between lines of filament near the top of the head).  I tried printing without spiralizing with a one-nozzle-width wide wall and and a top thickness of a mm or so but that's ugly as the light coming through the model shows the internal structure which I absolutely don't want.

  Anyway: adaptive layers would actually fix this problem except when I printed it the top of the head melts.  The layers are apparently very thin and the plastic keeps getting run over by the hot print head.

  Any suggestions on how to fix?  If there were a post-processing g-code extension to make minimum layer time much greater the last few vertical mm's of the print that might work but I don't find such a thing.  Is there?  I haven't tried changing the extruder temp with ChangeAtZ v5.1.1 ....maybe that'd work but I kind of doubt it.

Underextrusion?  Something else?  I saw this https://community.ultimaker.com/topic/10953-top-of-print-melting and haven't tried it yet.

  I'm playing around with the parameters in Adaptive Layer Height now but wanted to reach out and see if anyone had a similar problem and maybe a solution or suggestion.

 

 

 

[gr5 2,167]

Please show a photo of the "melted top".  Otherwise, the advice you get here is often useless.

 

For parts with small top layers (like the top of the eiffel tower for example) we indeed get melting issues where the PLA never gets a chance to cool enough (not a problem for other materials as they are all higher temperature).  The best solution is to print a tower next to your part that is taller.  When the head moves over to the tower the part gets a few more seconds to cool.  Alternatively I will print 2 or three of the same part.

 

Position the tower left or right of your part (assuming your fan(s) are on the side) such that the fan is hopefully blowing on the part while printing the tower.

 

[splitsecond 0]

Here is the melted top of the head figure mentioned in the previous post:

 

same print slightly different light angle to bring out different details

 

In the meantime I got a somewhat better result (just printing top of head since the rest of the model prints fine and I don't want to waste time and plastic).  Some settings:

Ultimaker Original

print in PLA

Layer height: 0.25mm  (I'll do 0.1 or 0.15 for final version after fixing issues, but for sake of speed in testing, 0.25)

Wall thickness: 0.6mm (nozzle diameter)

Spiralize

Smooth Spiralized Contours

Speed 90mm/sec.

Temp: 214°C

Adaptive max. variation: 0.27mm

Adaptive step size: 0.03mm

Adaptive layer threshold: 200

 

It's almost usuable, at least there's no hole.  I'm not sure what to tweak next to get rid of the peaks and valleys.  Maybe reduce extruder temp at that z-height.

 

 

Below was the first attempt, for reference.  Just spiralize, no adaptive layer height.  I think the layer height was 0.15mm and the overall height 120mm, that hole about 30x38mm.

 

Edited August 21, 2019 by splitsecond

[Smithy 1,144]

I would say you print too fast. 90mm/sec is too much and with the small area at the top the material has no chance to cool down.

If you print slower, you might be able to go down a bit with the temperature, but you would have to test that.

 

In addition, the model is not easy to print in spiral mode. At the head end you have a massive overhang and since you only have one perimeter, little contact area. The material in this region is almost printed in the air.

 

So I'm not sure it'll print the way you think.

[splitsecond 0]

ok, thanks for the thoughts.  I will keep testing things and if I succeed will post a pic.'n params.

[Smithy 1,144]

Good luck and I hope it works out. Such a head in spiral mode surely looks great.

[gr5 2,167]

Do the tower thing I talked about.  Why didn't you do the tower?  It makes a HUGE difference.  It's easy.  You just need a cube and you can resize the cube in cura with the scale feature (unlock the 3 axes so you can make it

 

10mmX10mmXslightly_taller_than_model

 

When you go to print the hole thing to make it only 10mm on a side or it might fall over.  As a general rule towers should be 1/5 as wide as they are tall to not fall over (to be nice and safe).

 

[splitsecond 0]

I didn't do it yet as I have other things going on but I will try it.

[burtoogle 513]

23 minutes ago, gr5 said:

Do the tower thing I talked about.  Why didn't you do the tower?

 

But then it will not be possible to use spiralize and there will be all the normal z-seam unhappiness to contend with.

[burtoogle 513]

Coming late to this thread. I assume you are using adequate cooling with a lot of fan for the top layers?