Blender, Joining, Transparent objects?

[Lucy Rust]

I am somewhat new to Blender, but have been putting in my time and beginning to understand it. I am creating basic models and understand UV unwrapping (for the most part.) I am using 2.7.  I have created a model for a bomb shelter entrance. The model is a cylinder, with a torus handle (with the number of faces dropped) and two cylinders as inner handles. I have managed to join the handles and the main cylinder, but the torus does not play well. When I try to join it to the rest the whole build goes transparent?

I've tried uploading without joining and that doesn’t seem to be an option (I get a parse error)

Am I missing something? Please help. 

[Pamela Galli]

You need to flip your normals, Lucy. 

[Lucy Rust]

Thank you so much. I selected the joined object, edit mode, A, then under mesh, normals > flip normals. 

Seems like there is some tiny thing every day that I learn about mesh. Should have come here long ago.

[Drongle McMahon]

It's easier to see this sort of problem if you turn on "backface culling" in the Blender 3D view. That makes the rendering one-sided, as it is in SL. You can do that in the "Display" section of the properties panel on the right of the 3D view.

[Chic Aeon]

Sometimes an object can be perfect with no problematic normal faces and when you join it to another "perfect" object, some of the faces flip. Oftentimes recalculate works but sometimes you actually have to select the problematic faces and flip them manually.

I haven't really seen a pattern to the why of the normal face issues. It does happen more easily if you are asking Blender to MAKE a new face. Happily I don't see those as often as I used to so I must be doing something a bit better .

Have fun.

[Pamela Galli]

This forum is a treasure for those of us trying to make our own mesh.

[Min Barzane]

This kind of joining error always happens when you dont apply position/scale/rotation on all objects before joining! If you dont apply one or more objects always get flipped normals!

[Medhue Simoni]

This also happens when you mirror a mesh and then join them together.