Impact device for directional boring

A directional boring apparatus, comprising:

• a drill string;
• a directional boring machine connected to a rear end of the drill string and capable of forcing the drill string through soil;
• an impact boring tool connected to a front end of the drill string, which tool includes a tubular housing, a head mounted at a front end of the housing for sliding, lengthwise movement relative to the housing, such that shortening of the tool occurs as external force on the impact tool in its lengthwise direction becomes greater, the head including a chisel configured for breaking loose rocks and stones encountered in soil, the chisel having a sloped surface that can cause the impact tool to change its boring direction when pushed forward by the drill string without rotation of the drill string, a striker disposed within the housing for delivering an impact force to the head, and a trigger mechanism which causes the striker to deliver an impact to the chisel only when an external force exerted on the impact tool in its lengthwise direction exceeds a predetermined level, wherein the predetermined level is the maximum amount of force capable of being applied by the direction boring machine and is insufficient to move the tool past an obstacle, such that the apparatus can bore through the ground with the impact tool inoperative when the external force exerted on the impact tool in its lengthwise direction fails to exceed the predetermined level;
• and
• the trigger mechanism including a spring which biases the head and housing apart such that the spring is compressed as the tool shortens, and the trigger mechanism resets when the tool is lengthened back to a starting position.

A method of directional boring using a directional boring apparatus including a drill string, a directional boring machine connected to a rear end of the drill string and capable of forcing the drill string through soil, and an impact tool connected to a front end of the drill string, which tool includes a tubular housing, a head mounted at a front end of the housing for sliding, lengthwise movement relative to the housing, such that shortening of the tool occurs as external force on the impact tool in its lengthwise direction becomes greater, the head including a chisel configured for breaking loose rocks and stones encountered in soil, a striker disposed within the housing for delivering an impact force to the head, and a trigger mechanism which causes the striker to deliver an impact to the chisel only when an external force exerted on the impact tool in its lengthwise direction exceeds a predetermined level, the trigger mechanism including a spring with biases the head and housing apart such that the spring is compressed as the tool shortens, and the trigger mechanism resets when the tool is lengthened back to a starting position, comprising the steps of:

• pushing the impact tool forward through the ground using the directional boring machine;
• rotating the drill string while pushing it to move the tool in a substantially straight forward direction;
• ceasing rotation of the drill string while pushing to change the direction of travel of the tool;
• actuating the trigger mechanism by causing pushing force exerted by the drill string to exceed a predetermined level, wherein the predetermined level is a level at which the external force is insufficient to move the tool past an obstacle, such that the apparatus can bore through the ground with the impact tool inoperative when the external force exerted on the impact tool in its lengthwise direction fails to exceed the predetermined level;
• and
• pulling back on the drill string to re-set the trigger mechanism after actuating it.

A directional boring apparatus, comprising:

• a drill string;
• a directional boring machine connected to a rear end of the drill string and capable of forcing the drill string through soil;
• an impact boring tool connected to a front end of the drill string, which tool includes a tubular housing, a head mounted at a front end of the housing, the head mounted for sliding, lengthwise movement relative to the housing, such that shortening of the tool occurs as the external force exerted on the impact tool in its lengthwise direction becomes greater, and a trigger mechanism including a spring which biases the head and housing such that the spring is compressed as the tool shortens, the head including a chisel configured for breaking loose rocks and stones encountered in soil, a striker disposed within the housing for delivering an impact force to the head, the trigger mechanism causing the striker to deliver an impact to the chisel only when an external force exerted on the impact tool in its lengthwise direction exceeds a predetermined level, wherein the predetermined level is a level at which the external force is insufficient to move the tool past an obstacle, such that the apparatus can bore through the ground with the impact tool inoperative when the external force exerted on the impact tool in its lengthwise direction fails to exceed the predetermined level;
• and
• a coupling at a rear end of the housing for attaching the drill string to the tool.

An impact boring tool, comprising:

• a tubular housing;
• a boring head mounted at a front end of the housing;
• a striker disposed within an internal chamber of the housing to deliver an impact force to the head by lengthwise movement within the housing;
• a first spring confined within the housing such that rearward movement of the striker away from the head compresses the spring;
• and
• a trigger mechanism having an engagement surface that engages the striker and holds it in a position in which the first spring is actuated, wherein the trigger mechanism releases the striker to cause it to deliver an impact force to the boring head when an external force exerted on the impact tool in its lengthwise direction exceeds a predetermined level.