How do I prevent damn randomly flipped normals?


I spent 4 hours creating myself a gun model. It is around 900 polys. I checked texture mode every once in a while. It all looked fine.
So, when I actually look at it in Render or the Game engine, it is all screwed up. Normals flipped at random.
I’ve been slowly hand flipping them for around 2 hours now and am nowhere near complete.

When modeling, how the hell do you prevent those stupid things from happening? How are you supposed to know without rendering or playing the game if it is modeled correctly?

I love blender; but this normal thing pisses me off so much. It makes me sick at my stomach when I spend all of my free time making this, getting ready to enjoy it just to find out that I have to spend double the time just to FIX the model.

Run Recalculate Normals. In Edit Mode with the faces you want to calculate selected, you can go to the Mesh menu under Normals. The key shorts are there as well.

Scroll down to where this picture is:

or select everything in edit mode and press CTRL+N then enter, or click.

Sometimes, when that doesn’t work fully, you can select the flipped faces and type W->flip normals.
I’ve found that setting the display to Multitexture Mode can be be an easy way to find “flipped” faces: they show as transparent.

Another handy tip:

If you have a large flat or curved surface where some normals are reversed and some aren’t, select one that’s reversed and do Select -> Linked Flat Faces, and specify an angle tolerance. Linked flat faces will only select faces that are joined, within the angle tolerance, and have the same normal direction - making it a fairly quick and easy way to select all of the reversed normals in some situations.

Also, in the ‘Mesh Tools More’ tab of the Edit buttons window (appears whilst in edit mode on an object) there is a box you can check to get it to draw normals in the viewport. This allows you to see instantly if any are the wrong way. It’s handy because big normal flipping issues usually stem from one error which you have built out from. If you catch that error straight away it makes life a lot easier.