You are speaking about drilling a socket hole. In that case you are drilling.
I am talking about the first part of the job which was to enlarge the cut-outs for the PU's ears, if you will.
You can't enlarge a part of a hole with a drill bit and not have problems with wandering and chatter. You need to replace the material that was removed where the body of the PU sits adjacent to the ear cut-outs then drill and enlarge a whole hole, if you get me, not part of one.
Hope this helps clarify my awkward wording.