Core Drilling Core drilling is a process used to create precise round holes in both horizontal and vertical surfaces. Common applications for core drilling may include test cores, dowels, anchors, and penetrations for plumbing, electrical, and HVAC. Donley Concrete Co. can drill ½” diameter to 60” diameter holes with unlimited drilling depth. Donley offers various core drilling equipment based on the job requirements. Based on the application, core drilling can be electric or hydraulic hand held or mounted to the surface which can be vertical, horizontal, angled, or upside down.