Chile ? An enormous drill began preliminary work Monday on carving a half-mile chimney through solid rock to free the 33 men trapped in a Chilean mine, their ordeal now having equaled the longest known survival in an underground disaster.

The 31-ton drill bored 50 feet into the rock, the first step in the weeklong digging of a “pilot hole” to guide the way for the rescue. Later the drill will be outfitted with larger bits to expand the hole and pull the men through — a process that could take four months.

The men were trapped Aug. 5 in the San Jose mine in Chile’s northern Atacama Desert. Before rescuers dug bore holes to reach them, they survived 17 days without contact with the outside world by rationing a 48-hour supply of food and digging for water in the ground.