Mitring

Also called: mitreing, mitering

A mitre is a joint that splits a corner angle exactly in half, with each piece cut to that bisecting line, so the two pieces meet edge to edge instead of one overlapping the other. It evenly divides both the inner and the outer angle of the corner between the two pieces.

What mitring is for

At an external corner, mitring carries a moulding's shaped profile around the turn, hiding the end grain, the surface left where the wood is cut across its fibres, that a square joint would otherwise expose. A framed joint can be formed by cutting a mitre on every member that meets at the corner, and edge banding, the strip fixed along the edge of a panel, is fitted piece by piece with each end cut to a mitre. Angled sash-window sills, on multi-frame windows set at an angle to each other, may be joined either with a halved and screwed joint or with a mitre secured by a handrail bolt, a bolt used to draw a mitred joint tight. A mitre between two straight lengths of moulding is itself a straight line; a mitre between two curved mouldings follows their shared curvature, provided both pieces are curved to the same shape.

Cutting a mitre

The plainest tool for the job is an ordinary mitre block, a simple guide the work is laid against for the saw. Shop-built jigs go further: one pairs an angled fence with a finely adjustable stop block, a block set to fix where the cut falls, for precise mitre cuts on a table saw, though the workpiece can creep along the fence during the cut and spoil the result if it is not held firmly. For a hand-cut compound mitre, a mitre cut on two axes at once, the bevel angle, the angle the blade or cut leans at, is marked on both ends of a guide block and then planed to that line.

Mitring with mortise-and-tenon frames

Mitres are also cut where a moulded frame meets at a corner over a mortise-and-tenon joint. Setting the tenon in from the rail's bottom edge keeps it hidden once the mitre is cut. In one worked sequence, a rail and leg are fitted together first, and the mitre's starting point is then marked on the rail from the position of the leg; on a back rail carrying muntins, the vertical dividing bars of a frame, the edge, face and back are all marked together for the tenon shoulders, the flat faces cut where a tenon steps in from the width of the rail, the muntin mortises and the mitre cuts at the same time. Paired angled stiles, the upright side members of a frame, are set face to face so their edges can be marked together for mortises, haunches, the short stubs left on a tenon to fill part of a groove, and mitres in one operation.

Scribing as an alternative to mitring, and its tools

Coping is the term for a joint made without a mitre at all: the end of one moulded piece is cut to the reverse of the other's profile, and the two interlock instead of meeting on a diagonal. In sash-bar joinery, where a window is divided into panes by thin moulded bars called sash bars, a shaped templet, a pattern piece cut to guide the cut, is sometimes used to scribe the glazing bars, cutting one piece so its end follows the reverse of the moulding's profile; but mitring the moulding on both sides of the bar first, then working from that, can give a cleaner scribe outline than the templet method.