Value of sliding dovetail construction

The benefits of interlocking, sliding dovetail construction have been well-known for a long time. They are self-squaring, self-aligning and self-locking, joining two cabinet components in a way that is very strong and that shouts “quality” to even the most casual viewer. But of even greater value to small- and medium-production shops is the fact that they allow all the components in a piece to be fully finished in the flat before the piece is assembled.

We all know that finishing flat components is faster, involves less waste, and allows nearly anyone in the finish area to produce a higher-quality finish than can be achieved when trying to finish a fully assembled piece. The problem in the past has been that making interlocking sliding dovetail joints has required great skill achievable only by the best of craftsmen.

Within the last couple decades, innovation — launched first by the German company Festool and now being introduced by most major tool manufacturers — is bringing the ability to produce interlocking sliding dovetail joints to even the least experienced of your workforce. The key is guided rail routing and special work tables that make it easy to hold work pieces flat without moving.

A “T” shaped track on these new style guide rails holds a plunge router against both in- and out-thrusts, while keeping it on a perfectly straight line. Once the intended line of cut is established, it is easy and fast to align the guide rail, set the intended depth of cut for the female dovetail groove and make that part of the joint perfectly, time after time. The guide rail does all the work and the router can be moved in either direction with equal ease and equal result. There is little skill required on the part of the operator.

Note that this is very different from asking your operators to hold a router against a traditional fence or guide as they move the router along the intended line of cut. If the router is moved in the direction that has the router bit pulling the router towards the fence, and if the work piece is straight-grained, stable and free of imperfections, most of the time a reasonable dovetail groove can be cut. The problem using these traditional-type fences or guides comes when the work piece has figured, uneven or wild grain (often some of the most spectacular solid woods), or when the cut must be made in the opposite direction where the router bit tries to pull the router away from the fence or guide. Most of the time, the groove will not be perfectly straight and the work piece is ruined. Not a good situation in any production operation.

Self-guiding
What these modern guide rails do is hold the router firmly against both in- and out-thrusts so the guide rail, not the operator, ensures a quality outcome, no matter which direction the router is moved relative to the direction the bit turns.

Here is where that really becomes important: Let’s say you want to produce a chest of drawers that has inset drawer faces and dust panels between each drawer bank. You need some way to locate those dust panels so they are exactly aligned side-to-side and in exactly the correct location up and down the chest so the inset drawers will fit properly. The easy and accurate way to do this, and add significant visual value to the piece at the same time, is to clamp each side component inside face up with the front edges touching and properly aligned onto a flat reference surface — one of those special work tables mentioned earlier. Now lay out the center lines for each of the dust panels along the back edges of the two side components.

Place a new style guide rail aligned with the first centerline, clamp the guide rail in place, mount a dovetail bit in a plunge router, and set the desired cut depth. The operator simply moves the router along the guide rail to produce the female dovetail groove in both cabinet sides at the same time. Those grooves must line up properly since they were cut at the same time in both sides. Leave the two sides clamped together and flat on the work table and move the guide rail to the next female dovetail groove center line and make the next cut.

Note that the operator can move the router either direction since the new style guide rails holds the router on line no matter which way it moves. You don’t need your most experienced people to do this operation. Even the modestly trained can do it perfectly time after time. If you don’t want the dovetails to show from the front side, just have the operator cut from the back side towards the center, but stop short of the front edge on both sides. That’s the beauty of being able to cut in either direction with equal ease and result.

Continue making all the female dovetail grooves for all the dust panels. They will all correctly align since they are all cut in both pieces at the same time. No more referencing dados or dovetail grooves from the top on one side and from the bottom on the other side as you have to do if using something like a traditional router table or shaper or table saw (for dados) to make these critical cuts.

With all the female dovetail grooves cut in both sides of the cabinet, those components can go to the finish room to be fully finished in the flat.

The final steps
The dust panels require a male dovetail on each end that will slide in the female grooves cut on the inner face of each cabinet side. Once the dust panels are fabricated, the matching male dovetails can be cut most easily using a horizontal router where the dust panels can lay flat on the horizontal router table and be moved safely past the dovetail router bit held in a horizontal position. They also can be cut with a saddle fixture attached to the router or with a feather board jig to hold the dust panel upright on a conventional router table.

Once the matching male dovetails are cut on each end of the dust panels, they can go to the finish room in the flat as well. After both the cabinet sides and the dust panels are fully finished, even your least-experienced workers can do the assembly as the sliding dovetail joints will self-align, self-square and self-lock. With a bit of imagination, you will see how you can quickly solve complicated wide-grain to long-grain solid wood movement issues as well.

With even a modest investment in a modern guided rail routing system and special work tables to hold the components in place while the rotating cutter is moved past the stationary work pieces, your workers can turn out high-quality interlocking sliding dovetail pieces with a very low error or rejection rate. Story sticks can be employed to eliminate measurement errors in aligning the guide rails to the intended groove center lines. Your workers can turn out more pieces per hour, with greater satisfaction and little chance for error.

You’ll enjoy the value-added benefits of unusual dovetail construction that your customers will recognize, appreciate and value. And you will also enjoy the cost-reduction benefits from finishing all your major components in the flat before they are ever assembled, even for the first time.

Jerry Work is the principal of The Dovetail Joint in Kerby, Ore. More of his tips and techniques can be found at www.jerrywork.com

This article originally appeared in the November 2008 issue.