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I'm working on a cube in Blender. I just deleted one of the faces (the top face) of the cube and added solidify to avoid non manifold edges.

In this case, when I check the design it shows that the bottom face is an overhang face (shown with yellow color). However, if I change the overhang parameter in 3D printing tool box from 45 to 90° and then check the model, it doesn't show any overhang faces and it seems that everything is okay. I don't think increasing the overhang parameter could be a good idea. However, this is my first time that I'm trying to design a model for 3D printing. Can this model with the overhang parameter equal to 90° be printed using a 3D printer? How can I fix the overhang problem in this simple model.

Blender screenshot]

Today I tested another simple model. I used a fill circle and added solidify to the model. Although the model is really simple, check the model shows the same as the previous design - the bottom face is an overhang face. It seems that adding solidify to a shape leads to this problem. I don't know how can I fix this problem. Changing the overhang parameter fixes the overhang problem but it seems that this not a good idea for printing models.

Unfortunately, I can not test the print myself as I do not have a printer myself and I need to outsource the print job.

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    $\begingroup$ welcome to the 3D Printing Stack Exchange site. I hope you find find this a valuable location both for questions, and to help others with answers. Your question woule be better if you added a picture of the model. I am not a Blender user, and although your description may be perfect, I have trouble visualizing the model you are asking about. $\endgroup$ – cmm May 31 '19 at 16:45
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    $\begingroup$ It may not be a problem. Technically, the bottom face is an overhang face, but if it is sitting on the print bed, it doesn't matter. Have you tried printing a model? $\endgroup$ – Mick Jun 1 '19 at 13:17
  • $\begingroup$ Unfortunately, I do not have a printer myself and I need to outsource the print job. $\endgroup$ – Sara Jun 1 '19 at 15:01
  • $\begingroup$ Hi Sara, and welcome to SE.3DP. Do you know that there is a Blender Stack Exchange site..? Should I migrate your question there for you? However, after re-reading, your question is actually about printing an overhang, so maybe it is better suited here. Let me know what you think :-) Also, when you take a screen shot, maybe zoom in closer so that the model isn't so small. Also, please add information in the question and not the comments. I have put the additional info from the comments into the question. $\endgroup$ – Greenonline Jun 2 '19 at 7:06
  • $\begingroup$ Thank you very much for making changes. I did not know the blender stack exchang. But so far I have received good answers in 3d printing stack exchange and I am very grateful for that :). $\endgroup$ – Sara Jun 2 '19 at 8:01
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You are looking at overhangs in the design tool. What matters are overhangs when printing.

When designing the object, the coordinate system is convenient for working with the object. Before slicing, the object can be rotated and repositioned for better printing. Only after is it positioned for printing can the actual overhangs and bridges determined.

Unless you wish to limit yourself to the design tools coordinate system, I wouldn't have the design tool generate support material, and I would ignore its comments about overhang angles. First, bring the object into your slicer, position it on the print bed, and only then evaluate the need for support material.

To be honest, I often have a printing strategy in mind while I am designing an object, but when the object hits the printer I sometimes completely change my plan.

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Overhangs that are substantially greater than 45° to the vertical generally require supports, and overhangs of 90° will definitely require supports, unless they are bridges (supported at both ends). Depending on how well you have your printer and filament "dialled in", it is possible to print overhangs up to 70° without supports. However, if your model is a simple cube, it will have no overhangs, so it doesn't really matter what value you give the overhang parameter. Supports are usually generated when the model is sliced, but some modelling software will generate supports as part of the model.

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I'm a regular user of Blender and the 3D Printing add-on to design and print stuff. It will always consider the bottom of your model as an overhang, and it should pose no problem when you send it to print.

The add-on will say the bottom is an overhang because, in the virtuality of Blender, the object you're designing, like the cube in your picture, is floating in an empty void and the add-on has no setting to tell it 'this face is a bottom, don't check it for overhang'. I guess it could be programmed, but I'm not sure that it would be a good idea since it would then keep considering this face as the bottom even if you turn the object 180°.

You can safely ignore that particular warning from the 3D printing add-on when you send your object to be printed, as long as it is printed with the same orientation than in Blender. And it should be, since the export in STL will keep the orientation of the object along the X, Y and Z axis.

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