Double Margin drills have an additional margin ground behind the leading margin,providing twice the number of contact points.The second margin performs various functions to improve hole quality.
The trailing margin burnishes the cavity, making a true hole and smoother finish, helping to provide a more concentric drilled hole
A reamer finish can be achieved with double margin drills, eliminating a second operation.
When a double margin drill is used with a drill bushing, the four margins locate in the bushing, providing increased bushing support in excess of 200%.
When intermittent cutting is required, the double margin drill performs in two ways: Enhanced margin support in the first cavity cut, and support on breakthrough, which stops the drill from wandering when in contact with the work space.
Drill back taper is more tightly controlled than a regular drill, enhancing a rounder hole location.
135-degree split point provides immediate self-centering on contact with the work piece, and reduces thrust, due to its notch-type web thinning at the chisel edge length. The split point is excellent for drilling harder materials (titanium, stainless steel, and high temperature alloys.)
The bronze-gold drill color is an easy way to identify these tools as being cobalt aircraft drills, and is easy to group when resharpening.
With all these features incorporated in this double margin drill, it is excellent for hand drilling.