Is Cura Deranged?

[MrTechAgent 2]

So, as a beginner I had nothing but respect for Cura but over time I realised that it's pretty stupid.

I need some help from you guys who can tell me why is my print failing, I know why but don't know what's causing it, I'm pretty sure it's the slicing but I can't figure out what.

Here's the model -

As you can see I need to print in that orientation cause I don't want supports in a Ball and Socket joint also there's nothing wrong with the orientation anyway.

But....here's when things get interesting, when the stick begins to start it's first layer, the Z-Axis is almost too close to it for multiple layers until it goes up a few layers before the socket starts to print, the second half prints beautifully as the Z-Axis and Nozzle position is exactly as my levelling. I don't understand why Cura is being so difficult, this is such a simple model, my print settings were all perfect as far as I could tell -

Layer Height - 0.06mm

Speed - 40mm/s

Infill - 100%

Nozzle - 0.4mm

Shell Thickness - 0.4mm and 0.8mm (Tried Both)

Initial Layer thickness - 0.3mm

Here are pictures, these should clarify the slicing mess -

Sometimes Cura is the greatest free thing ever but other times it's just downright stupid as shit.

Any help solving this will be appreciated, I will also download the free sample of Simplify3D today and do the same print to know if it's a slicing issue or not.

Edited April 5, 2016 by Guest

[SandervG 1,521]

For the sake of testing, have you tried printing it with like.. 60% infill or less?

Does it even print infill or are the shells thick enough to touch / create the entire stick?

[tommyph1208 55]

Model isnt THAT simple, the "cup" part initially has quite an overhang to print, and the stick as you call it is quite thin...

If I had to bet I would say that Cura is slicing fine, but you have some setting problems that in combination with how these machines work, create your problems.

First off, you didn't post any temperature settings, but in general, the smaller the print (or part of a print), the lower the temperature you need... Printing that "stick" at a normal PLA temperature (~210 degrees) will melt and deform it as shown in your picture..

There are a few things you can do here:

1. Lower the temperature: When printing slow enough, you can print PLA at around 190 degrees, this will help the plastic solidify faster and reduce the constant heat radiation from the hotend while it is over the part.

2. Good cooling: make sure you have fans running at max, that they are working, directed properly etc. it really does wonders for printing small details and overhangs.

3. Print multiples at once: this is a common approach when printing small objects to help layers cool sufficiently before the next one is layed on top. Simply multiply the object in cura (say, 3 times) and enable the "print all at once" option under "Tools".

The minimum layer time setting you find in cura is there for the same purpose, but works poorly with small objects (like the stick part of your model), since it just slows down the print speed to match the layer time but the nozzle is still right over the entire (or most of the) model for the duration of the layer.

When printing multiples at once the printer will do travel moves between each model and allow the layers of each one to cool more before the next one is laid on top... As an added bonus you can pick the model that came out the best when done

3.B. Hone your retraction: Since printing multiples at once will cause travel moves, you need to have retraction enabled and somewhat honed in, in order to avoid ugly stringing on the outside of your part... The reduced print temperature greatly helps with this issue, and so will fast travel speeds, and some tests to get a good setting for retraction distance and speed (4mm. @ 40 mm./s is a good starting value... )

Edited April 5, 2016 by Guest

[avogra 68]

I see no error with Cura but your model is really tiny. There is not enough time between the layers to cool down. For this model I would print a larger pillar next to it. With a 0.25mm nozzle you can expect much better results too.

[gr5 2,229]

What tommy said #3 - print a tower next to it as high as the bottom of the cup. Your basic problem is that in the skinny part there isn't time to cool down and you get a globular mess - basically the nozzle is sitting in a glob of liquid plastic that never gets a chance to cool because the hot nozzle is *inside*.

The reason it recovers higher up is because it is farther from the heated bed. But the solution isn't to turn off the heated bed - it's to print a 1cm X 1cm tower next to your part. Or print 2 side by side.

[MrTechAgent 2]

Model isnt THAT simple, the "cup" part initially has quite an overhang to print, and the stick as you call it is quite thin...

If I had to bet I would say that Cura is slicing fine, but you have some setting problems that in combination with how these machines work, create your problems.

First off, you didn't post any temperature settings, but in general, the smaller the print (or part of a print), the lower the temperature you need... Printing that "stick" at a normal PLA temperature (~210 degrees) will melt and deform it as shown in your picture..

There are a few things you can do here:

1. Lower the temperature: When printing slow enough, you can print PLA at around 190 degrees, this will help the plastic solidify faster and reduce the constant heat radiation from the hotend while it is over the part.

2. Good cooling: make sure you have fans running at max, that they are working, directed properly etc. it really does wonders for printing small details and overhangs.

3. Print multiples at once: this is a common approach when printing small objects to help layers cool sufficiently before the next one is layed on top. Simply multiply the object in cura (say, 3 times) and enable the "print all at once" option under "Tools".

The minimum layer time setting you find in cura is there for the same purpose, but works poorly with small objects (like the stick part of your model), since it just slows down the print speed to match the layer time but the nozzle is still right over the entire (or most of the) model for the duration of the layer.

When printing multiples at once the printer will do travel moves between each model and allow the layers of each one to cool more before the next one is laid on top... As an added bonus you can pick the model that came out the best when done

3.B. Hone your retraction: Since printing multiples at once will cause travel moves, you need to have retraction enabled and somewhat honed in, in order to avoid ugly stringing on the outside of your part... The reduced print temperature greatly helps with this issue, and so will fast travel speeds, and some tests to get a good setting for retraction distance and speed (4mm. @ 40 mm./s is a good starting value... )

 

Hey,

The model is actually very simple and the printer has successfully printed it before, the successful print was on a different housing but the design stays the same, you can see it for yourself, printer had no issues with the overhang which was minuscule as the sphere was created linearly.

You can clearly see how "perfect" the stick is.

Answer to your questions -

1) I forgot, sorry...but yeah I printed at 210C.

2) Cooling did help but did not eliminate the issue irrespective of printing temperatures.

3) Good tip but it's still the nozzle touching and blobbing issue so even if I give it time the blob is persistent.

4) True but not really related to the problem.

Thanks for the tips anyway!

[MrTechAgent 2]

I see no error with Cura but your model is really tiny. There is not enough time between the layers to cool down. For this model I would print a larger pillar next to it. With a 0.25mm nozzle you can expect much better results too.

 

Way ahead of you, I tried 0.25mm but issue stayed because of the Z-Axis not going down enough and according to my leveling for the initial stick layers, it's a Cura issue cause I have printed the exact model before (Ball of the Socket but same thing) and it printed fine, I have attached that picture above when I replied to tommyph1208.

[MrTechAgent 2]

The reason it recovers higher up is because it is farther from the heated bed.  But the solution isn't to turn off the heated bed - it's to print a 1cm X 1cm tower next to your part.  Or print 2 side by side.

 

Didn't quite understand?

Are you talking about the Z-Axis blobbing in the initial layers of the stick part?

Edited April 5, 2016 by Guest

[MrTechAgent 2]

For the sake of testing, have you tried printing it with like.. 60% infill or less?

Does it even print infill or are the shells thick enough to touch / create the entire stick?

 

I did but it didn't make a difference as the size was too small for it to have less than full infill but I didn't try that with a 0.25mm Nozzle.

[gr5 2,229]

This "blobbing" issue you speak of is EXTREMELY COMMON on layers this tiny. I've seen this many times. I read EVERY post on this forum for the last 3 years. Please - I'm probably right about this. I could link you to 50 message 3 page topics about this but it's very simple.

In CAD create a cube of any dimensions. Drop it into cura next to your part. Click on it and scale it - unlock the dimensions. Set X and Y to 10mm. Set Z to a height that lines up roughly with the bottom of the spherical section. Print this next to your part so that while it is printing this cuboid the fans are blowing on the part you care about. Make sure "print all at once" is chosen and not "one at a time". Print it.

The reason it worked before - the red photo - is probably because it is just barely on the edge of working - 1C warmer air temperature 1% slower fan speed 1C hotter bed or 10C hotter nozzle temps is all it takes to push this over from working great to "the blob". Basically you were lucky before.

[gr5 2,229]

(sorry, it's a little frustrating when 2 people give you the correct answer but don't try it)

[MrTechAgent 2]

This "blobbing" issue you speak of is EXTREMELY COMMON on layers this tiny.  I've seen this many times. I read EVERY post on this forum for the last 3 years.  Please - I'm probably right about this.  I could link you to 50 message 3 page topics about this but it's very simple.

In CAD create a cube of any dimensions.  Drop it into cura next to your part.  Click on it and scale it - unlock the dimensions.  Set X and Y to 10mm.  Set Z to a height that lines up roughly with the bottom of the spherical section.  Print this next to your part so that while it is printing this cuboid the fans are blowing on the part you care about.  Make sure "print all at once" is chosen and not "one at a time".  Print it.

The reason it worked before - the red photo - is probably because it is just barely on the edge of working - 1C warmer air temperature 1% slower fan speed 1C hotter bed or 10C hotter nozzle temps is all it takes to push this over from working great to "the blob".  Basically you were lucky before.

 

Thanks, appreciate the help.

[nallath 1,124]

New cura has a cool head lift feature. Enabling that should also increase the results.

[MrTechAgent 2]

 Make sure "print all at once" is chosen and not "one at a time".  Print it.

 

So you were right gr5, the problem was fixed when I tried 'one at a time" but I was right about slicing, Cura is messing up something.

The initial layers and Z-Axis position with "one at a time" is perfect and is how it should be but the peculiar thing is when I do it solo, the Z-Axis doesn't go down enough and also the speed I think reverts back to the initial layer speed, almost as if it's considering initial layers of the stick as bottom layers.

The solution was simple but at the same time this error in slicing does exist and should be addressed, I think.

[tommyph1208 55]

 

 Make sure "print all at once" is chosen and not "one at a time".  Print it.

 

So you were right gr5, the problem was fixed when I tried 'one at a time" but I was right about slicing, Cura is messing up something.

The initial layers and Z-Axis position with  "one at a time" is perfect and is how it should be but the peculiar thing is when I do it solo, the Z-Axis doesn't go down enough and also the speed I think reverts back to the initial layer speed, almost as if it's considering initial layers of the stick as bottom layers.

The solution was simple but at the same time this error in slicing does exist and should be addressed, I think.

 

Don't you thin the print speed issues you are seeing are related to minimum layer time?

[IRobertI 521]

It could be a good idea if you shared the model and the settings (export them in cura so everything is included) and let us know which version you're using. That way it can be verified that it is indeed a bug in cura and not something with the model and/or the settings you're using.

Also, tommy is correct, the speed is being limited by the minimum layer time in an attempt to allow enough time for the tiny layer to cool.