Move object by a given distance on rotation of another (bolt & screw) I am looking to make a constraint to animate a cnc model. So i want to have a given object travel along an axis as a result of the rotation of another screw and bolt. 

To be specific a 360 degree rotation should move the child object 2mm limiting the rotations to 125 or 45 000 degrees for a total travel distance of 250mm.

Constraint should be able to work in both directions like a normal bolt and screw animation.

Thanks
Sounds like you need to set up a custom driver based on the rotation of the screw. This video is on corrective shape keys but is a good introduction to the use of drivers in animation 
https://www.youtube.com/watch?v=6mrceZ6fe-o