Tool-Design

Most operators know to change speed and feed when switching materials. Fewer know that the gun drill geometry itself should change. Running an aluminum-optimized drill in cast iron will produce poor tool life and inconsistent hole quality. Here is what changes and why. How Material Properties Drive Geometry Decisions Three material properties determine the optimal gun drill geometry: Chip formation. Materials that produce long, stringy chips (aluminum, low-carbon steel) need geometry that encourages chip breaking. Materials that produce short, broken chips (cast iron, brass) can use geometry optimized for edge strength. ...

I select gun drill geometry based on the material I’m cutting. In my experience, the geometry is the single biggest factor determining whether a job runs smoothly or produces scrap. I have seen shops spend thousands on premium carbide drills only to get poor results because the geometry was wrong for the material. The geometry of a gun drill’s cutting tip determines how the drill performs. Different geometries are suited to different materials and applications. ...