Drill breakthrough calculator finds the extra depth allowance needed for a drill’s conical point to fully break through material, based on drill diameter and point angle.
How it works
A twist drill’s tip is conical, so it doesn’t cut a flat-bottomed hole; the point continues past the nominal material thickness before breaking all the way through the back face. This allowance, added to material thickness, prevents programming a hole that stops just short of breaking through.
FAQ
Do I need this allowance for a blind hole? No. Breakthrough allowance only matters for through-holes. For blind holes, the point’s conical shape still affects the hole’s bottom geometry, but there’s no back face to break through, so this addition doesn’t apply.
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CNC Calculators · Through-Hole Drill Depth Calculator · Spot Drill Depth Calculator