Raise borer
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A raise borer is a machine used in mining for drilling a circular hole or shaft between two levels of a mine. The borer is set up on the upper level of the two levels to be connected. A small-diameter hole is bored to the level required, using a conventional drill bit - the diameter of this hole is only large enough to accommodate the drill string. Once the drill has broken into the open on the target level, the small bit is removed and a reamer bit, of the required diameter of the shaft, is attached to the drill string and raised back towards the machine. Any spoil from the operation falls away from the cutting surface due to gravity, removing the need for large amounts of water or drilling mud to remove the spoil, although some water may be necessary for cooling the reamer. Machine variants can also ream horizontal shafts via the same method.
The boxhole borer is a variant of a raise borer that is used when there is not enough space on the higher of the two levels to be connected. The boxhole borer is set up on the lower level, drills a pilot hole as a guide, then drives the reamer bit along the pilot hole from the lower level to the upper. Precautions have to be taken to redirect falling spoil from the machine, and to reinforce the drill string.
The term raise refers to a vertical or inclined opening which joins two levels of a mine.
The Beaconsfield mine collapse necessitated the use of a raise borer, operated in a boxhole manner, due to the need for minimal vibrations during the rescue.
