That used to be a standard fixture in door and millwork shops in the 60s and 70s. Around here they were called VisaDoor door routers. A door was laid on the bench, a template clamped down and the router was lowered from a counterbalanced cable. The router just swung in the air most of the time. It would punch through a solid core 1-3/4" door and rout out a hole for either for a grille or a light. Lots of people would try to rig them as router tables but they were just too big and awkward. I've had a few back in the day and yes, they were very heavy but that weight helped smooth out the door cutout operation.