Using truss rods
Instead of using mortise-and-tenon joints to build the base, use butt joints reinforced by truss rods, as shown at right. Available in kits, the rods can be loosened or tightened after assembly to compensate for wood movement as a result of changes in humidity. Rout grooves for the rods into the edges of the stretchers and the inside edges of the legs; the depth and width of the channels should equal the rod's diameter. Test-assemble the base and mark the groove locations on the legs and arms. Then bore a hole at each mark, making the diameter equal to that of the rods; countersink the holes so you can drive the nuts flush with the wood surface. Assemble the base, fitting the rods into the grooves and holes, and tightening the connections with washers and nuts. Cover the grooves with solid wood inlay if you wish to conceal the rods.
below shows a knockdown alternative to assembling the base with mortise-and-tenons.
The joints between the stretchers and the legs need to be solid, yet sufficiently flexible to be taken apart should you want to move the bench. Consequently, knockdown hardware designed for the purpose is often used to join the stretchers to the legs. The pages that follow detail some other methods of reinforcing knockdown connections.
Using machine bolts and wood blocks
To reinforce the connection between the legs and stretchers, glue a wood block of the same thickness as the stock to each edge of the stretchers. The blocks will increase the contact area between the stretchers and the legs. Once the glue is dry, cut a tenon at the end of each stretcher and a matching mortise in the leg. Fit the pieces together and bore two holes for machine bolts through the leg and the tenon in the blocks; countersink the holes. Make the connection fast by fitting the bolts into the holes, slipping on washers and tightening the nuts (right).
Using lag screws and dowels
Another way to strengthen a mortise-and-tenon joint between the stretchers and legs is shown at left. Cut a 1-inch-diame-ter hardwood dowel to a length equal to the thickness of the stretcher. Then bore a 1-inch-diameter hole through the stretcher about IV2 inches from its end. Also bore a hole for a lag screw through the leg, stopping the drill when the bit reaches the hole in the stretcher; countersink the hole so the screw head will sit flush with the surface. Fit the stretcher tenon into the leg mortise, tap the dowel into place in the stretcher, and drive the screw. Choose a screw that is long enough to bite through the dowel.
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