Roof drill bit and cutting insert therefor

Abstract

A roof drill bit has an elongate roof drill bit body having a forward end and a rearward end. The bit body includes at least one helical twisted surface terminating at a dust port and a feeder ledge proximate the at least one helical twisted surface. A hard insert is affixed to the bit body at the axial forward end thereof. The hard insert includes a plurality of leading cutting edges for cutting the earth strata. The at least one helical twisted surface and the feeder ledge enhance the flow of debris into the dust port.

What is claimed is: 
     
         1 . A rotary drill bit for penetrating earth strata, comprising:
 an elongate bit body having an axial forward end, the bit body including at least one helical twisted surface terminating at a dust port and a feeder ledge proximate the at least one helical twisted surface; and   a hard insert being affixed to the bit body at the axial forward end thereof, the hard insert including a plurality of leading cutting edges for cutting the earth strata,   wherein the at least one helical twisted surface and the feeder ledge enhance the flow of debris into the dust port.   
     
     
         2 . The rotary drill bit of  claim 1 , wherein the at least one helical twisted surface has a helix angle, HA, of between 10 degrees and 50 degrees. 
     
     
         3 . The rotary drill bit of  claim 2 , wherein the helix angle, HA, is 30 degrees. 
     
     
         4 . The rotary drill bit of  claim 1 , wherein the bit body includes a lobed socket in the axial forward end thereof, and wherein the hard insert includes a lobed projection, and wherein the lobed projection of the hard insert is received within the lobed socket in the bit body. 
     
     
         5 . The rotary drill bit of  claim 1 , wherein the bit body has a lobed projection projecting from the axial forward end thereof, and wherein the hard insert includes a lobed socket, and wherein the lobed projection is received within the lobed socket. 
     
     
         6 . The rotary drill bit of  claim 1 , wherein each one of the leading cutting edges for cutting the earth strata have a generally radial orientation. 
     
     
         7 . The rotary drill bit of  claim 1 , wherein each one of the leading cutting edges for cutting the earth strata have a corresponding side clearance cutting edge. 
     
     
         8 . The rotary drill bit of  claim 1 , wherein the rotary drill bit has a central longitudinal axis passing through a center point of the hard insert, and wherein the bit body has a peripheral surface, and wherein each one of the leading cutting edges for cutting the earth strata begins at a point radially outward of the center point of the hard insert and extends in a direction away from the center point so as to terminate at a point radially outward of the peripheral surface of the bit body. 
     
     
         9 . The rotary drill bit of  claim 1 , wherein each one of the leading cutting edges for cutting the earth strata is formed by a corresponding leading surface of the hard insert intersecting a corresponding top surface of the hard insert, and wherein each one of the leading surfaces are disposed at a rake angle of between 0 degrees and −15 degrees. 
     
     
         10 . A rotary drill bit for penetrating earth strata, comprising:
 an elongate bit body having an axial forward end, the bit body having a peripheral surface and containing a central bore, the bit body including at least one helical twisted surface terminating at a dust port and a feeder ledge proximate the at least one helical twisted surface, the bit body further including at least three debris ports in the peripheral surface communicating with the central bore, and each one of the debris ports has an axial forward edge, and the axial forward edge of each debris port is spaced a different distance away from the axial forward end of the bit body; and   a hard insert being affixed to the bit body at the axial forward end thereof, the hard insert presenting at least three discrete leading cutting edges for cutting the earth strata,   wherein the at least one helical twisted surface and the feeder ledge enhance the flow of debris into the dust port.   
     
     
         11 . The rotary drill bit of  claim 10 , wherein the at least one helical twisted surface has a helix angle, HA, of between 10 degrees and 50 degrees. 
     
     
         12 . The rotary drill bit of  claim 11 , wherein the helix angle, HA, is 30 degrees. 
     
     
         13 . A rotary drill bit for penetrating the earth strata, comprising:
 an elongate drill bit body having an axial forward end, the elongate drill bit body having a longitudinal axis, the axial forward end being defined at least in part by a discrete first axial forward surface that is generally perpendicular to the longitudinal axis and a discrete second axial forward surface that is generally perpendicular to the longitudinal axis, the first axial forward surface being axially spaced apart from the second axial forward surface, the bit body including at least one helical twisted surface terminating at a dust port and a feeder ledge proximate the at least one helical twisted surface; and   a hard insert being affixed to the axial forward end of the drill bit body so as to form a joint between the hard insert and the bit body, the joint being defined at least in part by the second axial forward surface,   wherein the at least one helical twisted surface and the feeder ledge enhance the flow of debris into the dust port.   
     
     
         14 . The rotary drill bit of  claim 13 , wherein the at least one helical twisted surface has a helix angle, HA, of between 10 degrees and 50 degrees. 
     
     
         15 . The rotary drill bit of  claim 14 , wherein the helix angle, HA, is 30 degrees. 
     
     
         16 . The rotary drill bit of  claim 13 , wherein the first axial forward surface is generally parallel to the second axial forward surface. 
     
     
         17 . The rotary drill bit of  claim 13 , wherein the drill bit body has a projection projecting away from the axial forward end thereof, the second axial forward surface defining a distal end of the projection, and the first axial forward surface being radially outward of the second axial forward surface. 
     
     
         18 . The rotary drill bit of  claim 13 , wherein the drill bit body includes a socket at the axial forward end thereof, and the first axial forward surface defines a periphery about the socket, and wherein the first axial forward surface is radially outward of the second axial forward surface. 
     
     
         19 . The rotary drill bit of  claim 13 , wherein the drill bit body having a central bore, the hard insert containing a first passage therethrough, the drill bit body containing a second passage therethrough, and the first passage in the hard insert being aligned with the second passage in the drill bit body so as to provide direct communication between the hard insert and the central bore of the drill bit body.