1. The hole is too deep.
Anything deeper than about 2.5× the tap diameter is no longer a shallow hole—especially in materials with high toughness and strength. In these cases, step tapping is necessary.
2. Very cheap taps or reconditioned (re-ground) taps.
Don’t even talk about stability here. Even if I went on site and did the job myself, the tap would still break.
3. Material hardness above HRC 28.
When machining materials harder than HRC 28, the cutting edges of ordinary HSS taps wear very quickly. If the tap isn’t replaced in time, it will snap suddenly.
Switch to a powder metallurgy tap, preferably with a small spiral, and you can even relax and take a bathroom break.
4. Poor machine performance.
If the machine’s feed and reverse are not synchronized, don’t rush it. Let the tap reach full depth, stop, then reverse and back it out.
Or have the boss spend some money on a floating (flexible) tapping holder—that should improve things.
5. Incorrect pilot hole size.
If the pilot hole is too small, the tap is clamped too tightly and torque becomes excessive.
If the pilot hole is too large, the cutting threads don’t actually cut, and the fully formed threads at the back are forced to take all the load—those are the ones that break.
So the pilot hole must be machined strictly according to the recommended size range.
6. Bro, stop staring at your phone.
Go find VOHIRL METAL and buy some powder metallurgy taps already.
Summary
Core takeaway: “Main causes of tap breakage and corresponding solutions.”
Five key causes of tap breakage:
Hole depth ≥ 2.5× diameter (especially in high-toughness, high-strength materials)
Use of cheap or reconditioned taps
Machining HRC 28+ hard materials with ordinary HSS taps
Poor machine accuracy (feed and reverse not synchronized)
Incorrect pilot hole size (too large or too small)
Targeted solutions:
Use step tapping for deep holes
Choose high-quality powder metallurgy taps (small spiral preferred)
Use a floating tapping holder, or tap to depth and then reverse out
Machine pilot holes within the recommended size range
