Sliding Dovetail Joint
Explanation: The real beauty of this joint is realized when joining cross directional grains such as with a table apron and its table top or when building a bookcase or other casework. When the sliding dovetail joint is used to attach a table apron to its top, the front edge of the table apron is glued and pinned using a dowel or other fastener and the balance of the table apron is allowed to move within the joint. |
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As the humidity changes from season to season, the amount of movement (expansion/contraction) of wood in the direction of the grain is much less than the expansion of the wood across the width of the grain. When a table side apron is glued along its entire length to the table top, the long grain of the apron cuts across the short grain of the top. As humidity increases, the long grain of the apron restricts the movement of the short grain of the top, placing the top in compression and crushing the fibers in the wood. When the season changes, the long grain of the apron again restrains the movement of the top, placing the grain in tension. After a few seasons of compression and tension, the fibers in the grain of the top fail, resulting in a checked (cracked) top. Using the sliding dovetail, the table top and the apron breath, expanding and contracting at different rates, sliding and thus preventing the cracking of the table top. |
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Making the Sliding Dovetail Joint |
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Mark the Position of the Dado |
Make a standard dado cut with a 1/2" straight bit |
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Replace the straight bit with a dovetail bit and adjust the Mounting Plate on the Trolley to cut a chamfer on one edge of the dado. Repeat for the other edge of the dado. |
Mount the mating piece vertically against the front of your workbench or make a shuttle that will straddle the end of the board. |
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Position the dovetail bit such that the neck of the bit barely touches the edge of the 1/2" dado that was cut 3/8" deep (in standard 3/4" dimension lumber). Without changing the depth of cut of the bit, cut the keys at the end of the mating pieces by positioning the mating pieces vertically as shown above or if using a shuttle set the work piece in place such that the end of the piece is flush with the top of the workbench or shuttle. Adjust the router mounting plate such that the neck of the bit again barely touches the edge of the lumber. The resulting cut will produce a key that is exactly the size of the dovetail cut into the first piece.
If your intent is to glue the entire length of the joint, it may be necessary to trim the width of the key by adjusting the router mounting plate a fraction of an inch (1/64) to take a light cut, repeating this step sneaking up on the just-right fit. The fit should allow the mating pieces to fit together across the entire width of the two pieces in one smooth sliding action. The glue will make the joint swell a little and if while assembling the pieces you momentarily stop movement, the fast setting glues will set up within seconds locking the pieces together. Use of slow setting glues makes the assembly go easier. Always dry-assemble the pieces before gluing to ensure that the fit and sequence of assembly is known. |
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Clamp the mating piece, in this case a shelf, so that it is flush with the top of the workbench or with the top of the shuttle. |
Clamp a guide rail section on top of the workbench parallel to the cut-line and adjust the position of the mounting plate on the Router Trolley to chamfer the end of the shelf. |
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Tight Fitting Joints |
Dry Fit-Up (no glue) |
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Finished Lamp Stand |
See this Red Oak Frame and Panel Bed and Lamp Stand in our Projects Page |
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