The present invention is directed to an improved drill screw. More particularly, the present invention is directed to a drill screw, and a method for making same, which screw has a pair of burrs formed along the cutting edges to protect them.
The present invention resulted during the manufacture of the screws shown in, and is related to the invention disclosed and claimed in, U.S. patent application Ser. No. 97,460 filed Nov. 26, 1979. Further, while tests indicate improved performance with other screw configurations, performance data indicate the most significant improvements occur with the configuration disclosed in the abovenoted application which disclosure is hereby incorporated by reference. For these reasons, the present invention is shown and described in terms of this particular configuration.
The conventional manner of manufacturing drill screws involves heading a screw blank, forming the flutes in the screw shank, and then pointing. The pointing step involves the use of pointing saws or cutters used to mill the end of the shank to form two terminal end portions whose intersection defines a chisel. The cutters are rotated in a direction to move material away from the cutting edge of one flute and toward the trailing or drag edge of the other. On some milling machines this results in a burr extending along this drag edge. This burr originates at the chisel and extends outwardly to the periphery of the shank.
For many standard platings, chloride-zinc for example, this burr presents no significant problem; the burr merely snaps off as drilling starts. But, for the heavier platings such as nickel or the multiple-coating platings, this burr becomes reinforced and the plating builds a deposit on the cutting edge producing two adverse results. First, the plated, reinforced burr resists snapping off since it enjoys a "protected" position in the drag region of the flute. This adds to the thickness of the screw in the chisel region and prevents the rapid penetration for which the screw was designed. In fact, if the build-up burr significantly increases the chisel dimension, the screw will spin rather than drill, creating heat which causes the point to break down. Second, the buildup on the cutting edge results in a lack of sharpness which detrimentally effects drilling.
The present invention solves the abovementioned problems by relocating the burr to a position along the cutting edge. Surprisingly, this does not merely form larger blobs on the cutting edges further degrading performance. Rather, the burrs protect the cutting edges from excess plating buildup. Because of the angular relationships of the cutters, the burrs are pushed away from the chisel region. This enables the drill screw to penetrate quickly and the plated burrs snap off as drilling continues and they are forced into the drilled material.
Other features, characteristics and advantages of the present invention will become apparent after a reading of the following specification.