What is the simplest way to rotate joints manually with the bones api?

Currently i'm using JointChannel/SkinClip/SkinClipSequence which works fine. But i'm reading the ogre bones.xml manually for this purpose, because i didnt managed to get the correct roations and translations from the binding matrices so far. Where is the joints binding matrix calculated?  While merging the two xml files or does this happens through the other used apis?