Graphical Construction Glossary >> Tools. >> Power Tools >> Rock Drill

Rock Drill

An air operated tool mostly hand held, that uses various sizes and lengths of drill bits for drilling into rock or concrete.

Photo above thanks to Wikipedia. Modern machines are almost the same design as this 1930's model.

Note! It is a carry over from the origins of these machines that even companies that use metric measurements normally still use imperial when describing the size and weight of air operated jack hammers and rock drills.

• I am talking about here the hand held drills from about 35lb weight to 75lb weight.
• They typically need 120 cubic feet per minute (CFM) at 90 pounds per square inch (psi).
• These rock drills have 3/4" swivel claw fitting to attach standard 3/4" hoses from portable air compressors which are their main source of power.
• Air operated drills like this one are capable of drilling 1-1/4" diameter holes in rock and concrete up to say 8 feet deep. Here I am guessing, as everything depends on the material being drilled.
• To do this they rely on the fact that the bits , or steels can be joined together as the depth increases.
• There are special bits that have a 3" diameter cutting collar that sits about 6" above the normal tip that make it possible to drill 3" holes in rock that are very convenient for grouting in pipes for fence poles.
• The reason that these machines are so good at what they do is that they have a (relatively) slow rotation rate and a high impact force that produces small chips rather than just dust like the faster action electric tools.
• The reason that these machines can drill so deep without jamming in the hole, is the fact the a portion of the exhaust air is fed down a hole in the center of the bit to blow the waste chips and dust out of the hole.
• In addition to that, there is a lever on the handle that switches off the hammer action and delivers all the available air down to the bottom of the hole to blast out out of the hole the dust and stone chips.
• Not using this manual control often enough is the main reason for getting the drill steels stuck in the holes.
• The deeper the hole, the more it should be blown out!

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