What to do when Blender behaves badly

There's nothing so frustrating as spending hours in Blender working on a model or tutorial and suddenly noticing things aren't working the way you expect them to. Your Mirror Modifier sends the mirrored image of into left field. Your Array Modifier snakes uncontrollably in the all directions. You go to add a new Loop Cut and your geometry shatters like broken glass.

The fixes for these problems are often buried in a tutorial somewhere or some online documentation. Most of us don't pay much attention to these valuable tips until disaster strikes. In the spirit of helping new Blender user get up to speed with this fantastic CG suite, I have put together some of these tips here to save time and frustration.

Select your mesh in Object Mode and press Ctrl+A then click Apply Object > Apply Scale and Rotation to ObData

This is a simple tip, but it fixes or prevents a variety of problems. It's best to apply this before you apply an Array, SubSurf or other modifier so that you will be starting with a "clean" object. You should try this fix if your arrays are going in strange directions or your SubSurf is badly deformed even though the geometry looks fine. You might need to use this fix if your Mirror Modifier mirrors along the wrong axis even though you have the correct axis selected. The reason why this works is because it re-aligns your object to the global coordinate system.

Object data before Ctrl+A > Object > Apply Scale and Rotation to ObData

Object data after Ctrl+A > Object > Apply Scale and Rotation to ObData

Note how the rotation data and scale data have been reset.

Use Remove Duplicates after applying modifiers like Array, Mirror or any modifier that creates new geometry

Unfortunately the modifiers that create new geometry often create extra vertices or faces that are not easy to spot until it's too late. Duplicate vertices or faces create a whole slew of problems. The symptoms of stray duplicates can be strange defects in textures, strange behavior when adding other modifiers, dark colored areas in what should be smooth meshes and difficulty in adding control loops to name but a few. You may not notice a problem until you hit the Apply button because that's when the modifier is converted to an actual mesh. The trick is to remove the dups immediately after your apply a modifier. That way you prevent problems later on. Just select your mesh in edit mode, select all the vertices, then press the W > Remove Duplicates. If there are any duplicates a menu will pop up to tell you. Just click it to confirm. If this breaks your mesh then you can adjust the Limit value in the Mesh panel and press the Rem Doubles button. Experiment with limit values to get rid of just the dupes. If that still doesn't work then you need to bite the bullet and remove them manually. Duplicate faces are more difficult to spot in a complex mesh. I have spent hours trying to smooth out a SubSurf modifier only to find that Blender had created duplicate faces over the faces of the original mesh. Examine your mesh carefully.

Subtle flaw introduced by duplicate faces.

Actual mesh with duplicate faces.

Same mesh with duplicate faces removed.

One trick that might help is to go into Edit Mode, select all vertices, and then go to the Mesh Tools More panel and press the Edge Length button. This prints the edge length next to each edge. Zoom into your mesh and look at the numbers. The zoom is important because a complex mesh may have lots of numbers. You should see one and only one number next to each edge. If you see two or more numbers next to what should be a single edge, then you have duplicates. You may also spot duplicate verts by seeing 0's next to a vert meaning that there are actually 2 verts right on top of each other.

Using Edge Length button turned on to expose duplicate verts and faces. 0.000 indicates that there are 2 verts in nearly the same spot.

Same mesh with duplicates removed.

The bottom line is that until you remove all duplicates none of the other fixes will work.

Watch out for the Object Center or Origin

If your still having problems with modifiers and transformations even after doing the other tips mentioned here then there's a good chance your object center has shifted. How can this happen? Easy. When you move your object in Object Mode the center moves with the object. When you move your object in Edit Mode the center does not move!! The Rotate/Scaling Pivot is usually set to Median by default so your modifiers and transforms will use the object center as the reference point by default. If the center has shifted you may notice scaling that is off, rotation does not work on the object's local axis, arrays do not follow a normal path as well as numerous other problems

Center of object is no longer at the center of the cube because the cube was moved while the object was in edit mode.

Rotating cube 45 degrees with the center in the correct location.

Rotating cube 45 degrees with the center shifted to another location.

Try these simple steps to get things working.

• Mirror Modifier - go into Object Mode and click the object you're trying to mirror. Take note of where the little origin is. This is the point along which your mesh will be mirrored. If it's not where you want it then select your object, go into Edit Mode, select all the vertices and move it to the spot that works for you. If you want a seamless mirror of your mesh then position it so that the edge you want to mirror along is on the object center.
• Array and other modifiers - these modifiers work best when the origin is at the true center of your mesh. To get it to true center, go into Object Mode, select your mesh object, go to the Mesh panel and press the New Center button. The origin will now snap into place. Your Array Modifier should work as expected now.
• Scaling and Rotating - These transforms work best when the origin is at the true center of your mesh. Go into Object Mode and select your object. Go to the Mesh panel and press the New Center button. This will move the origin to the true center of your object. Note that if you have an irregularly shaped mesh Blender will perform a complex calculation to find the center of the mesh based on all its faces and vertices. Your mesh should scale and rotate properly now.

If you plan to do any serious modeling and animation in Blender you need to fully understand the notion of "object center." Check the online Blender Users' Manual especially the section on Individual Object Centers.

Conclusion

These are some of the most common problems new Blender users encounter. I'm sure I'll be adding to this page in the future as people email their particular experiences. Until then, stay out of tall trees and rubber rafts. Happy Blending.