Few things kill momentum on a job like snapping a tap in an expensive part. The good news: tap breakage is almost always traceable to one of five causes, and all five are easy to fix once you know what to look for.
1. You're tapping to 100% thread engagement
A drill sized for 100% engagement leaves almost no chip clearance and dramatically increases the torque needed to cut. The industry standard of 75% engagement gives nearly the same shear strength while cutting tapping torque significantly. Use the Tap, Drill & Die calculator and stick to 75% unless you have a specific reason to go higher.
2. No chip clearing in blind holes
In a blind hole, chips have nowhere to go but back up the flutes. Pecking — advancing 1–2 turns, then backing out a half turn to break and clear the chip — is not optional in blind holes deeper than about 3× the tap diameter.
3. Wrong tap style for the application
Spiral-point (gun) taps push chips ahead of the tap — ideal for through holes. Spiral-flute taps pull chips up and out — use them in blind holes. A spiral-point tap used in a blind hole packs chips at the bottom with nowhere to go but break the tap.
4. Tapping too fast
Tapping speed should typically run 50–70% of your drilling speed for the same material. Going faster doesn't save meaningful time and dramatically increases heat and breakage risk, especially in stainless and tool steel.
5. Misalignment
A tap that isn't started perfectly perpendicular binds on one side of the flute and snaps under uneven load. For critical holes, finish with the tap still chucked in the spindle rather than by hand, or use a floating tap holder.