A broach is the little web between the consecutive holes of the channel. A continuous channel or cut slot would have to be cut into the granite floor. The process involved having a channel bar drill a row of holes that did not meet but came close together. The drill assembly traveled along the “channel bar” so that the holes would match…like a drill press.
Evolution of the Drill Bit
There are three stages (plus a pre-stage) of the evolution of the drill bit:
Pre-stage 1: A hand drill was used for blast holes. A bit would be struck with a sledge hammer (held by a succession of teenage apprentices) with one, two or three drillers striking a single, double or triple jacking! Stage 1: One piece is forged on the end of a drill steel. Stage 2: There is a detachable threaded bit that is made of steel as opposed to carbide. Stage 3: This would be a detachable carbide bit (widely used by 1950). Our quarry never got to this point in time. Stage 3a: Is step one in the evolution of the steel drill. Courtesy of the Becket Land Trust and Historical.