Resolve the connection before drilling
A hole in square or rectangular hollow section is part of a connection, not an isolated workshop operation. Load direction, wall thickness, edge distances, access and plate stiffness all matter. Through-bolts, blind fasteners, studs and other systems are not interchangeable; use the engineer's detail for structural work.
Confirm whether the joint must be removable and whether tools can reach the bolt head and nut. Do not cut an improvised access opening into a closed section. Verify any proprietary blind fastener against its manufacturer's data and the design requirements.
Establish one reference face and axis
Measure every hole from one face and one end datum. Mark orientation and part numbers, and use a verified jig where repeated parts are required.
Opposing holes for a through-bolt must share an axis. Support thin walls and prove the first part with the actual plate, washer and bolt before copying it.
Let the design set spacing
Hole position relative to an end, corner radius or adjacent hole changes net section and local behaviour. There is no universal edge-distance shortcut for every hollow section connection.
Do not elongate a misplaced hole with a grinder unless the approved detail permits it. Slotted or oversize holes change connection behaviour and require explicit design control.
Clamp the section securely
OSHA guidance calls for drill-press work to be clamped rather than held by hand. Use a stable cradle and support long overhangs without crushing a thin wall.
Keep guards in place, control loose clothing and hair, and use suitable eye protection. Stop the spindle before measuring, adjusting or clearing swarf.
Control drill, speed and feed
Use a sharp bit intended for steel and set speed, feed and cutting fluid for the material, coating and machine. Reduce feed as the bit breaks through to limit grabbing and exit burrs.
A two-sided drilling method is useful only when both centres meet accurately. Remove compatible cutting fluid before coating repair.
Do not crush a thin wall
Tightening a through-bolt pulls opposite walls together. Thin hollow-section walls can dish or collapse, so a larger washer alone is not a universal remedy.
Where designed, fit the specified internal sleeve, spacer or reinforcement to the correct length. Bolt grade or diameter changes do not automatically increase wall resistance; follow the specified tightening method.
Deburr and restore protection
Remove sharp burrs without enlarging the hole, and clear swarf from inside the section. Burrs prevent washers and sleeves from seating correctly.
Drilling exposes bare steel through paint, primer or zinc. Clean and repair the cut edge with a compatible system, and coordinate drainage and end closures for exterior work.
Approve the first joint
Dry-assemble the first connection using all production components. Check free bolt passage, washer bearing, wall shape, tool access and hole position before releasing the batch.
Record the section, wall thickness, drawing revision, fastener, tightening procedure and coating repair. Structural capacity must be verified by the responsible engineer, not judged by appearance.