US Patent 10058929 Step drill bit with variable helical flute

A step drill bit can include a cutting head defining a longitudinal axis and multiple steps having different effective diameters. First and second cutting edges can be formed in the cutting head. The first cutting edge and the second cutting edge can be arranged such that the bit is asymmetric in a plane perpendicular to the longitudinal axis relative to a plane containing the longitudinal axis. The step drill bit can further include one or more flutes. Each flute can define a groove in the cutting head that extends along a helical path about the longitudinal axis. Each flute can have a variable helix angle such that the angle of the helix about the longitudinal axis changes at one or more points along the length of the flute.