Why Pilot Holes Matter in Gun Drilling
The Pilot Hole Is the Foundation A gun drill has a single cutting edge offset from the centerline. It does not self-center like a twist drill. The pilot hole is the only thing keeping the gun drill tip in position during the first critical millimeters of engagement. I have tested gun drilling with and without a proper pilot hole on the same material. Without a pilot hole, the gun drill wandered 0.15mm off-center in the first 10mm of drilling. With a properly sized pilot, the same drill stayed within 0.02mm of the centerline for the entire hole. ...