The drill is used to make a hole in the stone, usually at 90° to the surface, that has a uniform diameter its entire depth. In the Roman period the standard form of drill was the strap or cord drill. This consists of a bit, usually a chisel-like metal tool, set into a shaft connected to a wooden handle within which it can rotate freely. The shaft is moved by pulling back and forth on a cord wrapped around it several times. This cord is operated by one person while another directs the drill itself, applying pressure on the handle and deciding where the bit is placed. The speed of rotation and the pressure applied can both be varied. Since the drill operator is free to use both hands to direct the drill and apply pressure the cord drill is more flexible than most other types of drills (such as the staff drill or bow drill) which are operated by just one person. Peter Rockwell notes that the cord puller was often an apprentice and had to work hard to keep up with the drill operators actions: ‘I have been told by workers who were trained with this tool that the strap puller, usually an apprentice, learned quickly because he had his head slapped every time the cord slipped off the shaft, something which can happen quite easily’ (1993: 37).
The drill was used for a variety of tasks. These included creating holes for dowels or metal fittings but mainly it was employed to achieve depth in delicate areas of carving where the chisel might cause damage. To achieve a deep channel a row of drill holes would be created next to each other, at 90° to the surface of the stone, and the bridges between them then knocked out with a fine flat chisel or channelling tool of some description. Rows of drill holes which were not joined together can be seen on a range of Roman monuments and become increasingly common from the third century AD onwards. The cord drill could also be used as a running drill. Using a wooden support held in one hand to guide the drill bit, the drill operator would drill into the surface at a 35-45° angle, lifting the drill out and moving it slightly along continually to create a series of holes which are at such a shallow angle to the surface of the stone that they look like a channel. The Roman carver Eutropos depicts himself and his assistant, on his grave plaque from Urbino, using a cord drill in this way to finish the detailing on a sarcophagus.