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Step drill geometry formulas

A step drill combines two or more diameters in one tool, allowing a hole with a counterbore, countersink, or multiple diameters to be drilled in a single operation. The step length must provide adequate chip clearance and tool strength.

• Step diameter list: Ø1, Ø2, Ø3 etc. -- from smallest to largest
• Step length ≈ |diameter1 - diameter2| × 3 -- approximate transition length
• The step transition should have a chamfer or radius (not a sharp corner) to prevent stress concentration

How to use this Step Drill Design Calculator

Enter the two step diameters. The calculator shows the step diameters and an approximate step transition length. For custom step drills, send the exact diameters and lengths to your tooling supplier with the shank diameter and overall length specification.