Weird bone deformation

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  04 April 2013
Weird bone deformation

Hi everyone.

I have a certainly annoying problem with some weird bone deformations. Basicly, whenever I move or rotate a bone in my model, it deforms. The model is linked to the bones with a Skin modifier, so when the bone deforms, the mesh deforms as well. I can't go on to the animation part with this problem (obviously). Here you have some pictures of the problem:

This is the model before rotating the bones:

And here it is after rotating the head bone:

I think the problem is quite obvious, you should be able to notice the horrible deformation of the head in the second picture. The head bone is the only bone that's having this problem. This bone is linked (with the "Select and Link" tool) to the torso bone (this bone does not deform whit rotation, only the head bone).
I think I have already seen other people with this problem, but the solutions that were given to them did not work for me (or I didn't understand them correctly). Any solutions?

Kind Regards
  04 April 2013
Looks like you scaled the bone or it's parent.
Do not scale anything in a hierarchy.

If you need to adjust the bone's size, use the bone tools.
You may try to resetXform the bone and readjust the size, to avoid deformation of the mesh, turn 'Always Deform' off in the skin modifier.
  04 April 2013
Thanks for your reply.
Well, I may have scale something (I don't really remember), but adding a Reset Xform and readjusting the bone did not work (it still deformed after that). Actually, I deleted the old bone and created a new one (making sure I didn't edit or scale the new bone at all), and it still deforms.

However, I found something that could help find a solution: the deformation only happens when I use the "Select and Link" tool to link the head bone to the torso bone. I unlinked them, and the head bone didn't deform at all. Why?
I obviously need the head to move with the torso, so they have to be linked. But when they are linked, the head bone deforms when it's rotated.

Kind Regards
  04 April 2013
You need to make sure the parent bone is not scaled either. Suppose Bone A is linked to Bone B in that case if bone A was scaled bone B will deform when rotated.

I hope i make sense.

Its the scaling of parent bone that causes this not the bone itselt
  04 April 2013
Originally Posted by scrimski: Looks like you scaled the bone or it's parent.

Read more carefully. If it's not the head bone, then go one step up in the hierarchy. If I were you I'd replace the whole rig. If there's one scaled bone it's likely that there are others.
  04 April 2013
I see... it's because of scaling in the parent bones (sorry, I should have read more carefully your reply). Well, I guess the entire rig was messed up then.

I ended up remaking the rig, and this time I adjusted the bones' size with the Bone Tools, not with the Scale tool. The deformations disappeared! I hope I won't make the same mistake again on my next works.
Thank you all for the help!

Kind Regards
  04 April 2013
Never scale anything ever in a rig. Just don't do it!
Paul Neale
  04 April 2013
This is kind of an old tool now (Rigging Army Knife v1.8), but I still use it in place of the built in Bone Tools. It has a Rebuild Bones button that will create a new hierarchy based on positions without the unwanted scale.

Of course I never need it because my skeleton are always perfect.
Juan Martinez | Blog | Animator
  04 April 2013
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