Several companies have tried to buy there own drill rigs.  Industry in general doesn't like to see it.  None of the majors even buy there own rig, you need to specialize in that side of the biz.  One of the issues is what happens when you break down and only have the one or two rigs.  You have guys sitting on the sidelines twiddling.  You need to have a large parts inventory, bits, drill fluids, etc.  Also keeping valued staff around is a major thing to accomplish.  You would be stunned at how much more efficient certain drillers are than others.  It isn't uncommon to have one driller double the number of feet drilled per shift than other crews on the same project.

Look at the oil industry... they even contract drilling services.