Methods of drilling; dust-collector unit.

§ 33.35 Methods of drilling; dust-collector unit. (a) General. All drilling shall be done with conventional, commercial drilling equipment—pneumatic-percussion, hydraulic-rotary, and/or electric-rotary types—in accordance with the applicant's specifications. (b) Pneumatic-percussion drilling. A stoper-type drill with a piston diameter of 2 1/2 to 3 inches shall be used for roof drilling, A hand-held, sinker-type drill with a piston diameter of 2 1/2 to 3 inches shall be used for down drilling and also for horizontal drilling, except that the drill shall be supported mechanically. Compressed air for operating the drill shall be supplied at a gage pressure of 85–95 pounds per square inch. Drill bits shall be detachable, cross type with hard inserts, and shall be sharp when starting to drill each set of 10 holes. In roof drilling, 1 1/4 - and 1 1/2 -inch diameter drill bits shall be used; in horizontal and down drilling, 1 3/4 -inch diameter bits shall be used. The drill steel shall be 7/8 -inch hexagonal and of hollow type to permit the introduction of compressed air through the drill steel when necessary to clean a hole during drilling. (c) Rotary drilling. A hydraulic-rotary drill with a rated drilling speed of 18 feet per minute free lift, capable of rotating drill steel at 900 revolutions per minute with 100 foot-pounds torque, and having a feed force of 7,000 pounds, shall be used for roof drilling. An electric-rotary drill, supported by a post mounting, with a rated drilling speed of 30 inches per minute and powered by a 2.25 horsepower motor, shall be used for horizontal drilling. For roof drilling, the bits shall be hard-tipped, 1 3/8 and 1 1/2 inches outside diameter, and 1 1/4 -inch auger-type drill steel shall be used. For horizontal drilling, the bits shall be hard-tipped, 2 inches outside diameter, and 1 3/4 -inch auger-type drill steel shall be used. Drill bits shall be sharp when starting to drill each set of 10 holes.