Unibit with replacement blade

Abstract

A unibit with replacement blade provides economical refreshing of the many cutting facets of a unibit drill bit with a unibit replacement blade that is releasably secured in the unibit body. In one aspect of the invention, a replacement blade with cutting edges on one or both opposite side edges is releasably locked into the unibit body by a transverse locking screw. The blade can be provided with an integral tip drill when desired. In another aspect of the invention, one or more replacement blades is releasably secured in a recess in the unibit body with a simple blade lock mechanism, the blades being positioned symmetrically around the axis of the drill. In one embodiment, the blade lock is an eccentric cam member that rotates into and out of locking engagement with the blade. Other blade locks include clamping screws, screws through the blade, cam plates, tapered blades, and blade receiving grooves. Another aspect of the invention provides a replaceable tip drill.

1 . A unibit with replacement blade comprising: 
 a body of rotation having an axis, the body including a generally conical head having a base and a tip at opposite axial ends thereof and having an inclined outer surface extending between the base and the tip, the head further including a mounting shaft extending axially from the base for mounting the unibit in a rotating tool;    the head including an axially extending recess in at least one side thereof, the recess being formed in the outer surface of the head and extending inwardly toward an interior of the head;    a replacement blade that fits in the recess, the blade having a stepped cutting surface on at least one outer side that extends outwardly beyond the outer surface of the conical head, such that the cutting surface of the blade engages edges of a hole in a work piece before the work piece engages the head; and    a blade lock that releasably holds the blade in a secure cutting position in the recess in the head.    
   
   
       2 . A unibit as in  claim 1  wherein: 
 the recess comprises an axial slot extending laterally all the way through the conical body such that the sides of the slot are open at opposite sides of the inclined outer surface of the head;    the blade fits in the slot and includes stepped cutting surfaces on at least one of two opposite sides edges of the blade, the sides with stepped cutting surfaces protruding beyond the inclined surfaces of the body at the sides of the body; and    the blade lock comprises a fastener that engages the blade and locks it in position in the body.    
   
   
       3 . A unibit as in  claim 2  wherein: 
 the blade lock fastener comprises at least one locking screw that engages a threaded opening formed in the body transversely to the slot and extending from the inclined outer surface into the slot, the locking screw engaging and locking the blade in the slot when the screw is threaded into the opening, the blade being releasable by axially withdrawing the screw from the slot.    
   
   
       4 . A unibit as in  claim 2  wherein the blade includes stepped cutting surfaces on both of the opposite side edges of the blade and both side edges extend outwardly beyond the inclined surfaces on both opposite sides of the body.  
   
   
       5 . A unibit as in  claim 2  wherein cutting surfaces on the blade extend all the way to a tip end of the blade, the cutting surfaces at the tip serving as a tip drill to initiate a hole in material to be drilled.  
   
   
       6 . A unibit as in  claim 2  wherein the blade has a generally flat tip end without tip drill cutting edges for initiating a hole in previously undrilled material.  
   
   
       7 . A unibit as in  claim 1  wherein the blade lock comprises at least one fastener that extends through an opening in the body that extends transversely across the slot, the blade having a mating opening through which the fastener fits when the blade is in a mounting position in the slot.  
   
   
       8 . A unibit as in  claim 7  wherein the blade lock includes at least two spaced fasteners that extend through spaced openings in the body and blade.  
   
   
       9 . A unibit as in  claim 1  wherein the blade lock comprises a threaded fastener that extends first through an opening in the body on one side of the slot then through a mating opening in the blade, and then engages a threaded opening in the conical body on the opposite side of the slot.  
   
   
       10 . A unibit as in  claim 9  wherein the fastener has a head that includes a conical surface on an underside thereof, the conical surface engaging the opening in the blade and serving to center the opening in the blade with respect to the fastener.  
   
   
       11 . A unibit as in  claim 2  and further comprising stability means for enhancing the stability of the blade and proper positioning of the blade in the body, the stability means comprising a mating projection and slot in the edge of the blade and interior of the handle recess that properly positions the blade in the recess.  
   
   
       12 . A unibit with replacement blade, comprising: 
 a body of rotation having an axis, the body of rotation having first and second opposing ends, the body having a shaft extending along the axis toward a second end from the first end, the body having a head extending toward the first end from the second end, the head comprising two blade support members separated by an axial slot, with the head having a tip at the second end and a base at an opposite end of the head; and    a replacement blade releasably secured in the slot, the blade having two inclined sides, with cutting edges on at least one of the sides, the cutting edges including a series of steps and ramps of increasing diameter, the blade being secured in the slot so the cutting edges extend beyond the body in a direction that is radially outward from the axis.    
   
   
       13 . The unibit of  claim 12  wherein the replacement blade further includes a tip drill with a cutting tip at one end opposite the base.  
   
   
       14 . The unibit of  claim 12  wherein the replacement blade is releasably secured between the blade support members with one or more screws mounted transversely in the body for engagement with the blade.