How to orient objects so that SimpleTransform/Bend works correctly?

Question

SimpleTransform:Bend requires the object to be pre-rotated into an undocumented 'correct' combination of local and global rotations. Anything else causes the total fail of the code and you get the well-known fail cases (where it doesn't actually bend the vertices, and instead garbles them).

I have previously managed to find the rotations by trial-and-error but I can't seem to reproduce it. Some combination of rotating your object in the wrong orientation, Applying rotation, and then re-rotating back to the correct orientation, so that Bend is tricked into doing what it should have done in the first place.

The docs are a dead-end merely admitting that Bend needs an extra parameter (which is missing from the UI) and without that parameter it makes some bad guesses. They don't state either what the correct setup is, nor how to force Blender into that state.

So I can:

1. force it to fail, looking like this: https://developer.blender.org/T61523 -- all you have to do is rotate the object 90 degrees and Apply rotations, and Bend is now useless.
2. force it to succeed for one axis - the mesh's original X axis - by a different combination of rotations and Apply rotation

What I can't do is change it from working on the mesh's X axis to working on any other axis. Rotating the object then adding the modifier gives failure on all axis. Rotating the object, then Applying rotations, then adding the modifier gives success on the mesh's original X axis, but all others fail.

Answer 1

The modifier doesn't like half of possible orientations. Because it's dumb.
In that case you need to rotate 90° around the deform axis.

You can either:

• Rotate your geometry around the deform axis (often impractical)
• Rotate the origin
• Rotate a control empty

^{Rotating geometry around the deform axis - Z. Notice it only works in two of possible 4 positions.}

^{Rotating origin point (or an empty) around the deform axis - Z}