The 30cm-wide drill guided by a pilot hole half its diameter reached 633m beneath the surface, puncturing the top of a passage near the chamber in the San Jose copper and gold mine where the men have taken refuge. The next step is to place a wider drill on the rig and start a hole 71cm across - wide enough for the miners to get out.
The government previously said it would take until early November to rescue the miners under the most optimistic scenario, but Mining Minister Laurence Golborne said on Friday that now "we're a little bit ahead". The earlier estimate had built in the possibility of more setbacks than the effort has seen so far, he said.
Golborne did not provide a new estimate.
The government did not provide any reaction from the miners on Friday's breakthrough; it has made a habit of waiting a day to release video of the trapped men.
Point of pride
The miners have endured sweltering conditions for weeks, and the discipline and resiliency they have shown through their ordeal has been a point of pride among Chileans - perhaps especially so as the nation celebrates the bicentennial of its independence on Saturday.
The miners celebrated the bicentennial on Thursday, with beef and empanadas, and they decorated their chamber with a plastic Chilean flag.
Two rigs have been drilling holes separately to ensure that rescuers wouldn't have to start from the beginning if a major problem arose. A third, much larger rig is to begin drilling Monday.
The piston-driven air compression drills being used on the Schramm T-130 rig that broke through the passage chips away at rock like a jackhammer. Its hammers are made of diamonds, tungsten carbide and other alloys. The 12-inch drill was down for several days after a bithead broke - but still beat the more traditional competing drill down to the trapped miners.
Brandon Fisher, whose American company built the drills used on the T-130, said in a telephone interview with The Associated Press that the piston-based drilling system that will dig the larger hole will have four hammers instead of just one. Each hammer pounds independently, an average of 1 500 times per minute, he said.
The rest of the process will take weeks, but Fisher, of Berlin, Pennsylvania-based Centre Rock, Inc, said he could not estimate how long.
"There's just no way of knowing. We're drilling in extremely hard rock," Fisher said. "It's a volcanic conglomerate with a very high silica content and silica is the most abrasive substance that can be found in rock."
Once the larger hole is dug, it will be reinforced with a metal sleeve. The miners will be hoisted up in a steel "escape capsule" that is still being designed but will be fitted with oxygen tanks and a communications system.
Not a cakewalk
Widening such a deep hole has its dangers, including cave-ins that could trap the drill and halt the operation.
"By no stretch of the imagination is this a cakewalk," said Fisher.
The 38-year-old said he'd been working nearly straight for the past two weeks and was looking forward to eating and sleeping before resuming work.
"We hope to be drilling (again) in the next couple of days," he said.
The trapped miners work for a company with a history of safety violations that has pursued bankruptcy protection since the collapse and has said it can't afford to pay the men. They have been offered new jobs with larger mining companies in Chile that apply modern technology and safety standards to extracting the copper, gold and other minerals that provide for about 40% of the government's revenue.
http://www.news24.com/World/News/Miners-rescue-ahead-of-schedule-20100918
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