Importance

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Abstract

A method and apparatus for drilling a curved bore are disclosed, wherein the apparatus includes a handle (20) and a removable cartridge (174) in which cutting bits (240) are disposed to produce the bore. The handle includes a trigger (66), (66'), or (66'), which the user squeezes toward a grip (24) of the handle to both energize a pneumatic motor (42) and to advance the opposed cutting bits in curved arcs at different rates. As the trigger is squeezed, a curved guide arm (234) conveying one of the cutting bits is advanced more rapidly than the other curved guide arm, passing a median point in the bore and then being withdrawn as the other curved guide arm and cutting bit are advanced past the median point. Thus, interference between the two cutting bits is avoided and a clean bore hole is produced. In addition, the removable cartridge minimizes breakage of a flexible drive cable (238) used to transmit rotational force to the cutting bits from rotating left and right extended drive shafts (190 and 192). A straight segment (236) of each curved guide arm is provided adjacent the point where the cutting bit connects to the flexible drive cable, to substantially eliminate stress on the flexible drive cable at that point. Instead, the stress is shifted to a portion of the flexible shaft where its flexibility is greater. A push-button release (122) is provided on a barrel (26') of the handle to facilitate release of retainer pins (106') that engage push bars in the removable cartridge so that the removable cartridge can more easily be disengaged from the barrel.

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First Claim