Entry-Guidance

Why Pilot Hole Geometry Matters The pilot hole is the only thing guiding the gun drill during the first few millimeters of entry. If the pilot geometry is wrong, the drill starts off-center or at an angle, and the rest of the hole follows that bad start. I have measured the effect of pilot geometry on hole straightness across dozens of jobs. A pilot hole that is 0.1mm oversized produces a starting hole that is 0.05-0.08mm oversized at entry and the error propagates as the drill goes deeper. ...

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. ...