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Cura 3 showing smooth object but printing blocky

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Ok so I did some searching but not quite sure what wxactly to search for.  I’m new to printing and kind of new to 3D software.  I’ve downloaded a couple of items that have stl and obj files.  I can load the obj into Cura 15 and you can see all the flat areas like a lower poly object.  In Cura 3.1 it looks perfect and smooth like I want it to print, but when I look at the layers it looks like it sliced the lower poly that Cura 15 showed.  I’ll attach images. If you look at the image of the top view sliced, you can see the tail shows the blocky look is takingaboutas well as the body have flat edges instead of round.


2 questions

1. How do I print the high quality smooth obj that I loaded?

2. Why does Cura 3.1 show it smooth but not slice it like that?


thanks for any and all help ?




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The part is low poly (lowish).  It is what it is.  The bottom image looks smoother probably because they used some "smoothing" feature built into openGL which is the library that displays these polygons in 3D.  


Both obj files and STL files define vertexes and triangles.  They don't support the description of curved surfaces.  So it's just a matter of how high a resolution (how many triangles) you want - the higher the qty of triangles the smoother the surface gets.  At some point you are smoother than the curvature of the nozzle and there's no point and increasing triangles.


You could ask the original designer if they have a higher polygon version of the model.  I suspect when you print it you won't see the polygons anyway.  For the most part.

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Obj files can contain "normals" per vertex that basically "instruct" Cura to display the object smoothly. Cura should in my opinion ignore these normals. The problem is, Cura needs normals, so it should create a new set of normals that display the faces as is without smoothing (like legacy Cura did).

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I agree with @ahoeben that it should visually represent the actual model. This would remove any questions of this kind as a lot of users, especially noobs, are not used to the idea of polygon smoothing and what it will actually print. Also, if you have not seen the model in a viewer that displays the poly data properly, then this could be a nasty surprise.



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Thanks guys!  Thais definitely helps me understand the file better.  It makes sense that the normals in the obj file make it look smoother.  I just wish t would slice the normals.  It is the exact same file in both versions and that’s why I was confused.


@gr5 it’s not the most challenging I’ve done, but I did want it with as little vertices showing as possible.  I’ve had great luck with the supports in Cura 15 and am experimenting with Cura 3 so hopefully this one will turn out good.  I did a gyarados last week with it curling over itself and the supports on that were crazy lol.  It turned out perfect... imo ?

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On 2/3/2018 at 11:07 AM, gr5 said:

By the way - this is a challenging print - needs lots of support - lots of overhangs.


I had no idea how challenging it would be.  I've had a few mechanical issues, but I'm hashing those out.  Everything was good except the arm hanging down was only connected by the fingernail tips.  It's so high up that it got unstable before the arm attached to the body and the arm fell off twice.  I've slowed the infil and inner edge speeds, increased the supports size, adjusted the angle of the support "roof", decreased the distance the support is from the model and had it make a thick interface between the support and model.  It's going again right now.  The only other thing I can think of is pause the print when it's almost to the arm and attach the tower support to the body with tape or something before it gets to the arm so it does not move when the arm is printing.


I'm having fun learning, but this thing is testing the limits of my printer and my patience... :/

Edited by opy01

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