Can you help me ? I think I can explai It better now, I delete all my joints to try to simplify them, but still cant make my assembly move in the rails. I made an rigid group between all the moving parts of the Z axis ( of the 3D printer I'm designing, not the z axis of Fusion) , then I made the same thing with all the other moving parts(not the moving parts of the Z axis and not the base rails). Then I tried to make the Z movement by making a joing between the vertical linear rail( included in the second rigid group I made) with the linear bearing( included in the first rigid group, the one of the Z axis). But then my model stopped the relative Z movement. Then also when I try to make the as built join with the base rails, selecting the linear motion, my assembly also stops moving relative in the rail axis( they move together with all the other parts). So at the end, the only relative movement left is the movement of the red cart.