>>Hi Tom, it would probably help if you could post the 3DM model file as well.<<
I had uploaded it but sth went wrong - should be attached now !>>Do you want the gem object to deform at all or do you want it to only be moved and rotated?<<
The gem should not be deformed.>>If you don't want any deformation I'm not sure that there is actually any possible solution to the problem as stated<<
It seems to be difficult and that is why I decided to ask for ideas>>if the rails are not planar and have different lengths and different tightness of bending in them.<<
Ís there a solution if the rails keep exactly the same distance from each other ?