[mejunkhound]

broke when I was cutting through a larger rock

Sounds familiar. My first DIY drill was a rotary bit with teeth. 3 HP motor driving old IHC transmission via the flywheel gear, with the tranny in granny gear coupled to 2" pipe. I was extending my 18ft hand dug water well due to a 50+ house subdivision going in up the street.

Twisted the 1.3" dia output shaft off the tranny when it hit a big rock only 10 ft downhole.
So, machined a new shaft out of a 2" dia 4340M steel billet I happend to have,
Next thing happened on next rock was to strip all the teeth off the tranny bull gear.

Abandoned the rotary, built a walking beam percussion drill setup using a welded '62 Impala reah end to drive the walking beam. That went thru everything, including a 3 ft dia basalt boulder (judging by the number of bailers full of black rock chips). Blue clay layer at 60 ft with 5 ft fine sand above it (bottom of Puget sound glacier)

You may want to consider going to percussion drill? I posted a pic of my setup further back in this thread.

I see in a previous post in this thread that AC requested I add some data on my drill rig.
It is all pretty overgrown as quite a few years since last used but will try get some photos and post in a new thread tomorrow or next week. It is disassembled and laying in weeds but may be able to get enough pic to show the intent.