Drilling out bolts, studs, taps

How to use the calculator

Select what to remove (bolt/stud, broken tap, hardened fastener), M thread and pitch. Specify the strength class, drill type and equipment. Choose a strategy: keep the thread, use an extractor or restore with an insert (Helicoil, TimeSert, Ensat). The tool will calculate pilot drill, stage sequence, RPM and for Helicoil - drill and STI tap from the standard table.

Three removal strategies

Preservation of the thread - drilling to a safe limit (0.35×pitch less than the nominal value) so as not to cut off the remaining threads. Remains of fasteners are cleaned with a pick or tap. Applicable with bolt class 4.8–8.8 and sufficient wall.

Extractor (left spiral) - first drill out to 45% of d_core, then install the extractor or left drill. When drilling, the left drill sometimes unscrews the fragment on its own. Effective when the bolt is soured, but not hardened.

Restoration with an insert - drilling to the Ø for the insert, cutting the thread with a system tap (STI for Helicoil), installing the insert. Produces threads with the strength of the original or higher.

Frequently Asked Questions

Why does the drill break when drilling out a tap? HSS taps are hardened to 60–65 HRC - a regular HSS drill will not take them. You need carbide (monolithic carbide) or, best of all, electrical discharge removal (EDM). With EDM, the accuracy is high and the hole thread is not damaged.

What is Helicoil STI? STI (Screw Thread Insert) is a special profile tap for cutting threads for a spring insert. After installing the insert, its tail is broken off with a special punch. The final thread is metric, but strengthened due to a stainless insert.

What RPM to use with a hand drill? Aim for 60–70% of the calculated value. More important than speed is constant pressure and plenty of lubrication. The stand for a hand drill dramatically reduces drill drift.

Extractors, Helicoil kits, carbide drills - KARNASCH, RUKO, VÖLKEL - in our catalog.