How to reattach a mild-steel bracket to a steel cabinet

Steel to steel is one of the few pairings where adhesive genuinely competes with a mechanical fixing, and structural epoxies used in vehicle and panel assembly are the reason. What decides the outcome is not the adhesive, it is the surface and the direction of the load.

Mild steel is almost never clean. Under the paint there is usually primer, under the primer mill scale, and after a few weeks in a workshop a light film of oil and oxide. Epoxy bonds to whatever it touches, so bonding to a layer that is itself loosely attached gives you a joint that peels off carrying the paint with it. Abrading back to bright metal and degreasing immediately before bonding removes that whole failure mode.

The second half is geometry. A bonded lap joint pushed sideways spreads the load over the whole bonded area. The same joint pulled at one corner concentrates everything on a line a fraction of a millimetre wide, and that is why a bracket that seems rock solid can be levered off by hand. Increase the overlap rather than the thickness of the glue line.

1. Strip paint and remove any old adhesive from both faces with 80 grit until both are bright, clean metal.
2. Blow or brush the dust off, then wipe both faces with isopropyl alcohol on a lint free cloth and let it flash off.
3. Dry fit and check the two faces meet across their whole area. Pack or file until they do, because epoxy cannot make up a rocking joint.
4. Mix a structural two-part epoxy strictly to the ratio on the pack.
5. Spread a thin layer on both faces, working it into the abrasion marks rather than laying it on top.
6. Bring the parts together, slide them slightly to expel air, and clamp with light even pressure.
7. Wipe the squeeze out to a small fillet along the edges rather than removing it completely. That fillet is what resists peel.
8. Leave clamped for 24 hours, then give it a week before full load if you can.