Drilling performance of S235JR steel

Drilling S235JR structural steel is about as painless as it gets. This low-carbon grade is soft enough for high-speed steel (HSS) drills but tough enough to hold threads well. Whether you're making bolt holes, pilot holes, or through-holes, the process is straightforward – if you follow a few basics.

Choose the right drill bit. For most jobs, a standard HSS twist drill with a 118° point angle works perfectly. For production runs, step up to cobalt (HSS-Co) or carbide-tipped bits – they hold an edge longer and handle the heat better. Coated drills (TiN or TiAlN) add extra life in automated setups.

Speed and feed matter. For HSS drills, aim for 20–30 m/min surface speed – that's about 800–1200 RPM for a 10mm bit. Carbide? Push to 60–80 m/min. Feed rate: 0.1–0.2 mm/rev for smaller holes (under 12mm), dropping to 0.05–0.10 mm/rev for deeper or larger holes. Too fast? You'll burn the bit. Too slow? You'll work-harden the cut zone.

Coolant is your friend. Use a water-soluble cutting fluid or light oil. It reduces friction, flushes chips, and prevents the drill from seizing. For deep holes (over 3x diameter), peck-drill – retract every 5–10mm to clear chips and let coolant reach the tip.

Two gotchas: S235JR can form a built-up edge on the drill lip at low speeds – keep speeds up. And on thin sheets (under 3mm), support the backside or use a backing plate to avoid a ragged exit burr.