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Merged Models weirdness UM3 and Cura 2.4.0

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New to 3D printing so maybe it's a simple issue. I made a 2 part model (light squares and dark squares) in Blender for a chess board. After exporting each as STL files, importing, assigning extruder 1 and extruder 2, respectively, all looks fine. But when I go to print it, it draws a skirt around the model that is assigned to extruder 1, but invades the space of the second part of the model (see screen shot 1). If I select build plate adhesion, the brim is created around the first part of the model as if the second part doesn't exist (screen shot 2). If I print it, it appears that it is completely ignoring the first layer of the second part that is assigned to extruder 2. Screen shot 3 is layer 1 of the model with the second extruder selected. You can see that it shows the brim and nothing where the second set of squares should be.

So what am I doing wrong?

Screenshot 1

5a332888e9244_CuraScreenShot1.thumb.png.54884a63073aa21228a9b738e7161850.png

Screenshot 2

5a3328890d34d_CuraScreenShot2.thumb.png.8329b124a5bc136f8b5e0d355a2b2023.png

Screenshot 3

5a332889210f5_CuraScreenShot3.thumb.png.c008f1d2f037cdde60115de82fa7fa1d.png

5a332888e9244_CuraScreenShot1.thumb.png.54884a63073aa21228a9b738e7161850.png

5a3328890d34d_CuraScreenShot2.thumb.png.8329b124a5bc136f8b5e0d355a2b2023.png

5a332889210f5_CuraScreenShot3.thumb.png.c008f1d2f037cdde60115de82fa7fa1d.png

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Hello? Is this thing on?

Some more testing. Thinking the problem could be one of the STL files I tried several combinations and all of them still showed the same problem. I can load one STL twice, turn one 90 degrees to fill the chess board pattern and it still draws the skirt as if the second model isn't there. I can set both models to the second extruder and it still does it. Set both models to the first extruder, same thing.

I'd upload the STLs for someone to try but I don't see a file attachment feature.

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Looks like the tiles assigned to the second extruder are not touching the build plate.

You could try adjusting the Z axis down maybe by .1mm at a time until you get proper brim around everything.

Go back into Blender and verify that both sets of tiles are perfectly aligned at their bases on the Z-Axis and adjust if otherwise. Also make sure they are perfectly flat. If you have even the smallest protrusion on the bottom, Cura will use that as the part to touch the build plate.

Edited by Guest

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I did merge the models.

It does seem that it may have been the flat bottom issue pointed out by DaHai8. I reviewed the models and could not find any problems, but that doesn't mean there wasn't a tiny protrusion somewhere. So I redid the model very carefully making sure I kept everything aligned perfectly. But I ran into another problem because the two parts of the model wouldn't merge. I suspected it might be that the models conflicted in some way so I redid the models a third time and scaled each square to .99 cm instead of 1.0 but centered each square as if it was 1.0. Then it merged and I was able to print it.

This raises a question about merging models in general. Does Cura have a way of clipping models that overlap after merging? Complex models are almost sure to have those types of tiny imperfections.

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This raises a question about merging models in general. Does Cura have a way of clipping models that overlap after merging? Complex models are almost sure to have those types of tiny imperfections.

 

Yes. Depending on settings, but the defaults are:

Remove model 1 from model 2 on even layers and remove model 2 from model 1 on odd layers.

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