Attach imported stl models with one another using haptic feedback system?

We're trying to connect two (or more) stl models with another using the geomagic touch haptic feedback system. Importing stl works well and I think they are transformed into normal obj files once in unity. However, making one the child of the other, creates a problem with the haptic feedback system. The models don't work as they should and you can feel resistance where there shouldn't be any... Using a primitive such as a 3d cube as a parent and then attaching an "stl" works without any problems. Any ideas?