Corner brace

Overview

A corner brace is a piece of steel bent or cut into an L (or a flat plate with a diagonal) that is screwed to two members meeting at a corner. It stiffens the joint and keeps it square. It is a repair and a shortcut, not a substitute for joinery: a well-cut Wood screw-and-glue joint or a mortise and tenon needs no bracket, but a rail dowelled or butt-jointed to a leg may.

Types and sizes

• Flat L-brace for light frames.
• Gusseted brace with a rib across the corner, for shelves and tables.
• Corner plate / mending plate (flat) that sits on one face.
• Shelf bracket (visible, decorative).

Choose a plain steel one for hidden use; a brass one where it shows. Check that the screws supplied fit the holes; the loose, slim ones often do not.

Where it is used

Hidden under a tabletop to stiffen leg-and-apron frames, behind a bookcase back, on the underside of chair seats, and on shop furniture generally. No period style guide names them, since traditional work relies on joinery; they are the contemporary and utility answer.

Choosing and sizing

Use one per corner (four for a table underframe), with the longer leg laid along the grain of the rail. The brace's strength is limited by screw holding in the wood, so use a longer, larger screw with fewer holes drilled in the leg.

Installation

1. Hold the brace in the inside corner and mark the holes with a punch.
2. Drill pilot holes slightly smaller than the screw core (see Wood screw) and countersink if flush.
3. Drive the screws; do not overtighten, which can strip the thread or lift the corner out of square.
4. Check square with a try square before the last screw.

Wood movement and species

Fastening across the grain of a wide board with a rigid brace across the grain restrains movement and can split it. Use a slotted brace, or fix a brace to the end of a board with a slot to allow it to expand. In softwood and in end grain, screws pull out; fit blocks or use Threaded insert and bolts. In oak, steel braces and screws stain in damp air (see White oak).

Common mistakes

• Bracing a solid-wood panel rigidly across the grain: it cracks.
• Screws in end grain doing all the work: they pull out.
• Brace used to hide a poorly fitted joint: it racks over time.

Related

• Cross dowel and bolt and Bed rail fastener: stronger knock-down options.
• Shelf pin: adjustable shelves.