[Cura 4.8.0] Model does not sit flush on buildplate

[TheLoki 0]

Hi everyone,

 

I am at a loss and after many hours of googling I can not find any help to my problem.

It was hard to come up with a title for the thread, but basically my problem is that when I am slicing a model I made in Fusion360, what is supposed to be the bottom of the model only starts printing at the second layer.

 

I double checked the model and it has a perfect flat surface, I even aligned it with the bottom plane and made sure that everything is correct with the model.

I tested with PrusaSlicer and there the first layer get's sliced correctly. But as I have all my conifgurations in Cura and need specific features from it, I don't want to go through the hustle of using another slicer. But I assume when PrusaSlicer can correctly slice it that the issue is not with the model.

 

This is a screenshot of the model in Fusion360, as you can see, according to Fusion the whole bottom is one (flat) face.

 

I also tried several of Curas features ("Lay Flat", "Align Face") but the issue persists.

Even when lowered -0,2mm beneath the buildplate the hexagonal cutouts do not get sliced. And the parts that do get sliced are slightly thinner than the should be.

 

First import an alignment

 

After "Lay flat" and alignment:

 

Layer 1:

 

Layer 2:

 

I would really appreciate help on this matter.

As the model barely fits the buildplate, I cannot use a raft so I am highly dependend that the first layer goes down as perfect as it can be and a Z difference of 0,35mm isn't helping with that.

 

BR,

Loki

 

 

 

[nallath 1,120]

I think the features that you are trying to slice might be a bit too thin. Could you check it with the Beta release of Arachne?

[TheLoki 0]

I checked with the Arachne Beta but it happens there as well. Same result shown in the screenshots.

 

All the walls are 2mm in thickness and the connectors between the hexagons are 1mm in thickness and 2mm high. And it gets correctly sliced at the second layer and on. Only 1 layer too high.

 

What baffles me the most is that it does it even when submerging the model well under the bed. I deactivated "Drop model to buildplate" and lowered it to -1mm and the layer view showed the same image as in the screenshots but naturally only for 4 layers instead of 8.

 

Maybe as a sidenote: this also happens when no support are generated.

 

I attached the STL, maybe so we can rule out a general error and that it's only on my side or not.

If necessary I can also provide the F3D or the OBJ file.

 

SinkOrganizer_v2.stl

[Torgeir 242]

Hi @TheLoki,

 

I uploaded your stl file and sliced it for my UM2E+. The only printer I have that can -"hardly" print that object with.

So, had to deselect brim/skirt - set to none.

 

I sliced it with Archcne beta, standard profile (Normal 0.15) increased to 0.2 height..

Also used support with support blocker inside cause cura like to support inside, -no combing -but used retraction.

 

Layer one is all completed.

 

Here is how it looks.

 

 

 

 

Good luck

Thanks

Torgeir

 

 

[GregValiant 1,251]

Since Torgeir did the work with Arachne I went with 4.8.  I achieved the same results as Torgeir.  The first layer looked good.  The model appears to be sound with no errors.

 

I started playing with settings trying to get the first layer to disappear but I wasn't able to hit on a combination.

 

If you still have trouble do a "File | Save Project" and post the 3mf file here.  It will contain the model and all your settings.  Maybe somebody can see a conflict.

[TheLoki 0]

@Torgeir & @GregValiant thank you both for testing and verifying that the issue is something in my configuration. I don't know why it never occured to me to simply test another profile, but when I switched to the "Standard Profile 0,2mm" it worked.

 

For research purposes I've uploaded the 3mf file

CE5_SinkOrganizer_v2.3mf

 

For my issue I will simply tweak the standard profile (mostly speed and retraction) and roll with it.

 

I'm unsure what could possibly cause this behaviour. At first I thought it could be the first layer height of 0,35mm, but another PETG profile of mine has the same configuration and with this it is slicing correctly.

 

Anyway thank you all for your help.

 

BR,

Loki

[GregValiant 1,251]

The (-.5) Initial Layer Horizontal Expansion was too much for those thin cross-sections.  Setting it to "0" makes everything OK.  Related but not the problem - the Initial Layer Height of .35 is real tall for a .4 nozzle and if the first layer gap between the nozzle and bed is short by a bit it makes elephant foot worse because you are pushing a lot of plastic.  Backing that down to .20 or .24 may help with that.

 

With nothing to do while waiting for the sun to come up so I can go fishing (and do nothing), here are other thoughts...

I don't know if you have the model but in the black highlighted area, the vertical tubes aren't connected to the back wall.  Any weight in them will cause stress along the bottom corner where the back wall meets the bottom honeycomb.  I don't know if that is necessary to the part but the joining I've shown would be stronger (even if it's just the tube on the very end.  FDM parts just aren't as strong as "real" parts so they often need additional features to buttress them.

 

 

 

All the weight is going to hang off the top corners so those sharp inside 90° corners are high stress points.

With your settings, here is layer 624.

 

And here is layer 625.

 

 

You can see that the "top" is connected by very little material and counts on layer adhesion for strength.  Not good.

By adding some plastic at the top corners (either an inside radius/fillet like in the black highlight, or outside like in the red highlight) the durability would be increased.  This print is going to take the better part of a day to complete and it would be better if it held up for a while.  If it fails, it instantly becomes a "Sink Dis-Organizer".

 

 

 

Edited March 19, 2021 by GregValiant

[TheLoki 0]

@GregValiant thank you for taking your time and diving into this problem. It's interessting because I can't recall ever setting this feature, must have happened in dire attemps to fix some problems in the past 😄 Setting the initial layer to 0.35mm was also one of this attemps as in the past I had massive problems with the first layer sticking to the print bed. Since I use a glass bed and 3DLAC no such problems occured so 0.35mm on the initial layer is in fact not necessary anymore.

 

Thank you also for analysing my model. I am no material engineer or designer and never learned those things. So every bit of information is highly appreciated. I never considerd the stresses that occur on the 90° angles and on the tubes.

 

As the STL indicates this is V2. V1 is doing it's job since October, so I can access some experience with it.

 

 

The tubes are simply there for holding brushes, so the stress they transfer to the tubes aren't that high. I am sure that they will hold even when not attached to the back wall. But I will consider it as V2 hasn't been printed yet.

 

For the hooks, as you can see, here some more changes were made, I took a good bunch of material away. Before the stress would be distributed over the whole length/width of the organizer but with V2 it solely relys on the hooks. So strenghten these would really be a wise choice and I will definitley look into this. Thank you also for pointing in the right directions with the inside/outside fillet.

[GregValiant 1,251]

If it was an injection molded part then your design would work no problem.  I've found that functional parts need to be designed with FDM in mind because the strength isn't good when layers are in tension.  I've had to revise much of how I think about designing things since I started with the printer.  It's been an interesting journey.  For something simple like a phone holder for the wife I had to use wrap-around gussets.  It's in a hot car and wanted to deform without them.