Dovetail joints connect framing or panels with wedge-shaped mortise and tenon joinery. In a dovetailed corner, tightly fitting dovetails resist twisting forces and control solid lumber's tendency to warp. In post and beam construction, dovetail tenons resist forces that pull along the length of a beam. Properly fitted dovetail joints hold without pins, nails or glue.
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Full or through dovetails form the corner joints for wide panels. Multiple tenons and mortises provide a solid connection for the full width of the panels. Commonly used in cabinetry for carcass and drawers, full dovetails are exposed to view from the front and the side. The slope of the tenon varies with the type of wood used. If cut too acute, the tenons will slip and the joint will open--softwood requires a greater slope than hardwood. If cut too steep, the joints split under stress. Measure tenon slope by the old method of rise over run--one in six for softwoods and one in eight for hardwoods.
Half-blind dovetails hide the dovetail joint from the front view but leave it visible from the side. The wedge or tail pattern shows but the slotted look of the mortises does not. Cut tenons less than the full width of the panel for a half-blind joint, leaving a solid face on the front of the work.
Sliding dovetails securely join the edge of a panel to one face of another panel rather than to a corner. Use a sliding dovetail to fit a shelf securely to the back panel of a cabinet. Form this blind joint by shaping the back edge of the shelf into one long dovetail tenon. Cut a matching mortise no more than half the depth of the back panel. Slide the shelf's tenon into the mortise for a solid connection. Too perfect a fit may prevent complete assembly since friction increases as the long joint slides home.
Double-lapped or full-blind dovetail joints prevent the structure of a drawer from being seen when closed. A rabbet cut around the edge of the front panel reduces the width and length--the thin section that remains overlaps the socket that holds the drawer. Cut the dovetail mortises in the hidden section of the front panel and match the tenon length to them.
Mitred or French dovetails--also called full blind or secret--hide corner dovetails from any viewing angle. Cut rabbets along the ends of the mating panels and trim the laps to 45-degree angles. Cut dovetail tenons and mortises in the hidden edges of both panels to form the mitred full-blind dovetail.
In timber framing, similar joinery terms may refer to different types of joints. In log cabin construction, a corner dovetail joins two walls of stacked timbers, interlocking the walls with wedged tenons and sloping mortises. Instead of cutting the tenon square to the horizontal face of the timber, cut the tenon with a dovetail slope in two directions. A matching socket in the interlocking beam prevents the timbers from shifting in any direction. An ordinary full dovetail pattern would be solid in only one direction. In other timber joints, dovetail lap joints use a single dovetail tenon to match a half-lap socket in a second cross beam. Variations seem endless, since the dovetail is an integral part of many more complex joints.