The Deepest Hole by Alan Bellows:
In the 1960s the Soviet Union began a project to drill through the upper crust of the earth to reach the “mysterious area where the crust and mantle intermingle.” That project continued over 4 decades but they never were able to succeed. In order to drill at the depths they did reach they needed to engineer new drilling techniques.
Inside the project’s 200-foot-tall enclosure resides a unique drilling apparatus. Most deep-drilling rigs use a rotating shaft to bore through the ground– using a series of extensions which are incrementally added as the hole grows deeper– but such a method was unworkable with a hole as deep as Kola was planned to be. To overcome this, the Russian researchers devised a solution where only the drill bit at the end of the shaft was rotated. They accomplished this by forcing the pressurized “drilling mud”– the lubricant pumped down the drill shaft– through the specially-designed drill bit to cause it to spin.
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