Corner Joint — What It Is and Why It Matters
A corner joint is formed when two pieces of metal meet at an angle (typically 90°) to form an L shape. It is common in box structures, frames, enclosures, and sheet metal fabrication where two plates form a corner.
Corner joints can be welded from the outside (open corner — fillet or groove weld), the inside (closed corner — fillet weld), or both. The configuration depends on access, appearance requirements, and strength needs. Outside corner joints on thin material can be welded without filler metal using TIG fusion welding, producing a clean radius at the corner.
In structural applications, corner joints may require groove preparation for complete penetration. In sheet metal and light fabrication, simple fillet welds or edge welds are sufficient. The joint is straightforward to fit up using magnetic clamps, angle clamps, or tack-welded fixtures.
Frequently Asked Questions
How do I prevent burn-through on outside corner joints?
On thin material, reduce heat (lower amperage or wire feed speed), use a faster travel speed, and position the joint so both plates share the arc heat evenly. TIG welding gives the best control for thin corner joints. Tacking the joint thoroughly before welding prevents gaps from opening as heat builds.
What is the difference between an open and closed corner joint?
An open corner joint leaves a gap between the plate edges that is filled by the weld — common on thicker material. A closed corner joint brings the plate edges flush together, forming a tight L. Closed corners are typical in sheet metal and box construction.