Center Drilling vs Spot Drilling for Deep Hole Start
The pilot hole that guides the gun drill at entry determines the accuracy of the entire deep hole operation. I use center drilling for rotating parts and spot drilling for stationary parts. Getting this choice wrong creates problems that cannot be fixed later. Center Drilling: When and How to Use It Center drilling uses a combined drill and countersink tool to create a conical starting hole matching the gun drill tip angle. I use center drilling for rotating workpieces — shafts, axles, and cylindrical parts. ...