end portion 60 of shaft 20 and comprises a generally conically shaped portion provided with a helical thread 62 of substantially constant pitch as shown end portion 60 of shaft 20 projects axially outwardly from surface 30 of blade carrying portion 26 a substantial distance and is designed to engage the workpiece with self feeding helical thread 62 being operative to form a threaded engagement therewith and thereby draw boring tool 10 into and through the workpiece at a desired feed rate directly proportioned to the pitch thereof shaft 20 also includes an enlarged diameter portion 64 disposed between portion 58 and 60 which is received within portion 50 of bore 42 portion 64 includes an annular groove 66 adapted to be positioned in radial alignment with set screw 52 when shaft 20 is fully inserted into bore 42 and is cooperable therewith to maintain shaft 20 and body 12 in assembled relationship it should be noted that set screw 52 is positioned to engage shaft 20 on the side approximately opposite planer blade 18 and thus will operate to urge shaft 20 and end portion 60 into close proximity with the radially inner edge 67 of planer blade 18 thereby insuring more complete efficient cutting action of the boring tool and also serving to prevent fibers or other portions of the workpiece from becoming lodged therebetween and or wrapping around self feeding threads 62 and possibly interfering with or otherwise impairing the advancement of boring tool 10 through the workpiece it should also be noted that the cutting depth of each of the cutting edges 32 of spur cutters 14 and 16 and cutting edge 36 of planer.