Question 1

Taper shank drill vs annular cutter -- which is better for structural steel bolt holes?

Accepted Answer

Both tools are widely used in steel fabrication. Taper shank drills produce a solid hole by removing all material as chips, working well for holes from 14-50 mm in flanges and webs up to 40 mm thick. Annular cutters (core drills) cut only the periphery and eject a solid slug, so they are faster, require less power, and produce less heat on thick sections. For production shops drilling many holes in heavy sections (flanges over 25 mm), annular cutters on magnetic drills are more efficient. For smaller shops, mixed hole sizes, or situations where a radial drill press is already set up, taper shank drills are more versatile and lower cost per bit. Many fabrication shops keep both on hand.

Question 2

How do I set up a magnetic drill on an I-beam flange for field drilling?

Accepted Answer

Place the magnetic drill on a clean, flat section of the flange. Remove paint, mill scale, and rust from the contact area -- the magnet needs bare steel for maximum holding force. Engage the magnet and verify it is holding firmly before starting the drill. For inclined or vertical flanges, use a secondary safety chain or strap around the beam as backup. Position the drill spindle directly over the hole center mark. When drilling on narrow flanges, ensure the full magnet base is in contact with the steel; partial contact reduces holding force dangerously. Always use cutting fluid and moderate feed pressure to prevent the bit from stalling, which could break the magnetic hold.

Question 3

What are the bolt hole tolerance requirements per EN 1090?

Accepted Answer

EN 1090-2 specifies normal round hole clearances for structural bolting. For M12 bolts, the hole diameter is 13 mm (1 mm clearance). For M16, the hole is 18 mm (2 mm clearance). For M20, the hole is 22 mm (2 mm clearance). For M24, the hole is 26 mm (2 mm clearance). For M27 and above, the clearance is 3 mm. Oversize and slotted holes have separate specifications. The drill bit must produce a hole within these tolerances consistently -- worn or re-sharpened bits that cut oversize will result in rejected connections. Gauge-check holes with a go/no-go gauge during production runs.

Question 4

How do I prevent the drill from walking on curved or sloped beam flanges?

Accepted Answer

Drill walking on curved flanges (such as the inside of a rolled I-beam flange) is caused by the drill point contacting the surface unevenly. To prevent this: (1) Always center-punch the hole location firmly before drilling. (2) Start with a pilot drill (6-8 mm) to establish the hole center before stepping up to the final diameter. (3) Use a 135-degree split-point drill, which is self-centering and less prone to walking than a 118-degree conventional point. (4) On magnetic drills, ensure the base is firmly seated and the spindle is perpendicular to the flange surface. (5) Use moderate RPM and firm, steady feed pressure from the first contact.

Product	Size Range / Taper	Application
HSS Taper Shank Drill (M2)	14-50 mm / MT1-MT5	Standard structural steel bolt holes (S235, S275, S355)
HSS Taper Shank Drill (M35 Cobalt)	14-40 mm / MT1-MT4	High-tensile steel (S460, S690) and weathering steel (Corten)
HSS Taper Shank Drill (M42 Cobalt)	14-36 mm / MT1-MT4	High-strength low-alloy and quenched-and-tempered steels
HSS Straight Shank Drill	1-13 mm	Pilot holes, secondary steelwork, stiffener plates, gusset plates

Taper Shank Drill Bits for Structural Steel Bolt Holes -- H-Beam, I-Beam & Connection Drilling | Zhonghuan

Taper Shank Drill Bits for Structural Steel Bolt Hole Drilling

Recommended Products for Structural Steel Drilling

Application Scenarios

1. Beam-to-Column End Plate Connections

2. Field Drilling with Magnetic Drill on Erected Steel

3. Angle and Channel Connection Holes

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