How to drill a 4 inch hole in concrete
The walls at our new place are 6 inch thick concrete (it's an old Naval base) and we needed a few holes for vents. I've hammer-drilled through concrete to sink anchors, but a 4 inch diameter hole is a little intimidating -- until you have the right tool.
Here's a few pictures of the right tool. I only watched, so I don't know the finer details, but I thought people would appreciate just seeing the tool. The work flow went something like this:
1) hammer-drill and sink anchor to attach machine to wall
2) turn on machine; insert earplugs
It took quite a while, and that drilling noise reverberated throughout the whole place!