Boring bit and method of manufacture

Abstract

A boring bit has a shank, a head and teeth distributed around the head. The teeth have a root embedded within the head's core body, a tip extending out of the head, and a narrowing region between the root and the tip. More than approximately two-thirds of the tooth length is embedded in the core body, including a portion of the narrowing region. Stabilizing rods are welded to the tips of the teeth to form a temporary connection, and the core body is formed from a molten metal poured into a cavity of a cast mold. The rods are inserted into indentations in the cast to hold the teeth in place, and the molten metal heats the teeth and weld to substantially loosen the temporary connection. As the molten metal cools, it solidifies around the teeth and secures the root and narrowing region of the teeth within the core body.

What is claimed is: 
     
         1 . A boring bit, comprising:
 a shank portion;   a head portion connected to said shank portion, said head portion having a core body and a peripheral surface; and   a plurality of teeth distributed around said head portion, wherein each of said teeth has a root embedded within said core body, a tip extending out of said head portion away from said peripheral surface, a narrowing region between said root and said tip and a tooth length from a bottom of said root to a top of said tip, wherein said narrowing region has a decreasing width from a root width to said tip, wherein more than approximately two-thirds of said tooth length is embedded in said core body of said head portion, wherein said core body of said head portion covers a portion of said narrowing region.   
     
     
         2 . The boring bit of  claim 1 , further comprising a plurality of stabilizing rods, wherein each of said teeth has one of said stabilizing rods releasably connected to said tip. 
     
     
         3 . The boring bit of  claim 2 , further comprising a cast mold, wherein said cast mold forms a cavity and comprises an inner surface in contact with said peripheral surface and further comprises a plurality of indentations in which each tip of said teeth are embedded, wherein said stabilizing rods are encapsulated in said cast mold at said indentations and wherein said root and a portion of said narrowing region of said teeth extend into said cavity more than approximately two-thirds of said tooth length. 
     
     
         4 . The boring bit of  claim 3 , further comprising a weld forming a temporary connection between each one of said stabilizing rods and said tip of said teeth, wherein said core body is formed from a molten metal poured into said cavity, wherein said molten metal heats said teeth and said weld and substantially loosens said temporary connection while said molten metal cools and secures said root and said narrowing region of said teeth within said core body as said molten metal solidifies around said teeth. 
     
     
         5 . The boring bit of  claim 4 , wherein said teeth are formed from a carbide material having a first melting point at least 1,000° F. greater than said molten metal and wherein said weld is formed from a brazing material having a second melting point less than said first melting point by more than 1,000° F. 
     
     
         6 . The boring bit of  claim 3 , wherein said stabilizing rods have a rod length and wherein said rod length is greater than a length of said root and said portion of said narrowing region extending into said cavity. 
     
     
         7 . The boring bit of  claim 1 , further comprising a cast mold, wherein said cast mold forms a cavity and comprises an inner surface in contact with said peripheral surface and further comprises a plurality of indentations, wherein each of said indentations is comprised of a releasable connection with a corresponding one of said tip of said teeth. 
     
     
         8 . The boring bit of  claim 7 , wherein said core body is formed from a molten metal poured into said cavity, wherein said molten metal substantially frees said releasable connection between each one of said indentations and said tip of said teeth. 
     
     
         9 . The boring bit of  claim 8 , wherein said releasable connection is comprised of a stabilizing rod welded to said tip. 
     
     
         10 . The boring bit of  claim 1 , wherein said shank further comprises a mounting face, a pair of sides and a set of teeth embedded into said sides, wherein said root is comprised of a substantially cylindrical surface and a notch in said cylindrical surface, wherein said core body of said head portion is in fixed contact with said cylindrical surface and with said notch. 
     
     
         11 . The boring bit of  claim 1 , wherein said head portion further comprises an upper row of teeth, a lower row of teeth and a middle row of teeth, a top surface proximate to said upper row of teeth and a bottom surface proximate to said lower row of teeth, an angled surface between said shank and said top surface, a single passageway extending through said core body from an entrance in said angled surface to an exit in said bottom surface. 
     
     
         12 . The boring bit of  claim 11 , wherein said single passageway at said entrance is further comprised of a countersunk hole having an outer diameter approximately twice an inner diameter of said passageway, wherein said exit in said bottom surface is located at a substantially planar surface and is not located between a pair of said teeth in said head. 
     
     
         13 . The boring bit of  claim 12 , further comprising a drill stem with a nozzle extending to said passageway, wherein said drill stem has a longitudinal axis, and wherein said single passageway has a planform centerline aligned with said longitudinal axis. 
     
     
         14 . A boring bit for a horizontal directional drilling machine having a drill stem with a longitudinal axis and a nozzle, comprising:
 a shank portion comprising a mounting face, a back face, a pair of sides between said mounting face and said back face, and a plurality of mounting holes;   a head portion connected to said shank portion, said head portion having a core body and a peripheral surface, wherein said peripheral surface has a top surface, a bottom surface, at least one side surface between said top surface and said bottom surface, and an angled surface between said shank and said top surface, a single passageway extending through said core body from an entrance in said angled surface to an exit in said bottom surface, wherein said single passageway has a planform centerline aligned with the longitudinal axis; and   a plurality of teeth distributed around said head portion, wherein each of said teeth has a root embedded within said core body, a tip extending out of said head portion away from said peripheral surface, a narrowing region between said root and said tip and a tooth length from a bottom of said root to a top of said tip, wherein said narrowing region has a decreasing width from a root width to said tip, wherein more than approximately two-thirds of said tooth length is embedded in said core body of said head portion, wherein said core body of said head portion covers a portion of said narrowing region.   
     
     
         15 . The boring bit of  claim 14 , wherein said wherein said root is comprised of a substantially cylindrical surface and a notch in said cylindrical surface, wherein said core body of said head portion is in fixed contact with said cylindrical surface and with said notch and provides a positive lock between each one of said teeth and said head portion with said core body projecting from said cylindrical surface into said indentation. 
     
     
         16 . The boring bit of  claim 14 , further comprising a plurality of stabilizing rods, a cast mold and a weld forming a temporary connection between each one of said stabilizing rods and said tip of said teeth, wherein each of said teeth has one of said stabilizing rods releasably connected to said tip, wherein said cast mold forms a cavity and comprises an inner surface in contact with said peripheral surface and further comprises a plurality of indentations in which each tip of said teeth are embedded, wherein said stabilizing rods are encapsulated in said cast mold at said indentations, wherein said root and a portion of said narrowing region of said teeth extend into said cavity more than approximately two-thirds of said tooth length, wherein said core body is formed from a molten metal poured into said cavity, wherein said molten metal heats said teeth and said weld and substantially loosens said temporary connection while said molten metal cools and secures said root and said narrowing region of said teeth within said core body as said molten metal solidifies around said teeth. 
     
     
         17 . A method for manufacturing a boring bit, comprising the steps of:
 forming a cast having a cavity for a head portion with an inner surface and a plurality of indentations in said inner surface;   embedding a plurality of teeth in said indentations of said cast, wherein a tip of each of said teeth contacts said indentations and wherein a root of each of said teeth extends outwardly from said cast into said cavity of said head portion, said tip being less than one half of a tooth length and said root extending more than one half of said tooth length into said cavity;   creating a temporary connection between said tip of each of said teeth and said cast at said indentations;   pouring a molten metal into said cavity of said cast, said molten metal surrounding said root of each of said teeth and filling said cavity to said inner surface, wherein said molten metal heats said teeth and loosens said temporary connection between said tip and said cast.   
     
     
         18 . The method of  claim 17 , wherein said step of creating said temporary connection is further comprised of the steps of welding a plurality of stabilizing rods onto said teeth at said tip, inserting said stabilizing rods into said cast at said indentations and hardening said cast with said teeth and said rods in situ. 
     
     
         19 . The method of  claim 18 , further comprising the step of cooling said molten metal to solidify into a core body supporting each of said teeth at said root as said temporary connection between said tip of said teeth and said cast is loosened, breaking off said cast from a solidified core body with said stabilizing rods remaining in said cast, and drilling a passageway in said head portion through said solidified core body. 
     
     
         20 . The method of  claim 19 , further comprising the step of preparing a mold pattern for said cast, wherein said mold pattern includes a plurality of recesses for at least one of said teeth and a plurality of tooth blanks.