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This traditional joint ensures the only cup on your tabletop will have coffee in it.
The breadboard end is a traditional device for preventing a broad panel such as a tabletop from cupping. It is a narrow strip of wood that runs across the end of the main panel. Obviously, it must be attached in a way that allows the panel to expand and contract. But it also must be attached in a way that won’t allow the panel to cup without forcing the strip to bow. This means there’s got to be some form of interlock.
You should be aware of the aesthetic. The breadboard’s length won’t vary, but the width of the panel will. It may turn out that the only time the two dimensions match is when you construct the tabletop. Thereafter, you’ll have an endlessly varying difference. Get used to it. (If you want the look but can’t accept this quirk, use plywood for the panel and glue on the breadboard end!)
There are quite a few ways to attach a breadboard end. The drawing below shows several that are particularly good if your intent is to keep the top flat. In assembling any of these joints, glue is used sparingly, if at all. Most often, wooden pins are used to lock the breadboard, so it can’t pop off.
A single pin in a round hole at the center secures the breadboard but allows the top to expand and contract. If pins are added anywhere else along the joint, the holes for them in the tabletop must be elongated to allow for seasonal wood movement. Remember, the top itself will expand and contract, but the length of the breadboard won’t change.
For narrow breadboard ends, a tongue-and-groove joint works well. If the breadboard end is wider, adding mortise-and-tenon joints will add strength.
Establish the Proper Size
The width of the breadboard end and the length of the tongue, tail or tenon need to be in good proportion. A wide end multiplies the stresses placed on the joint. I think a good rule of thumb is to make the end no more than 1⁄2” to 3⁄4” wider than the longest element of the joint. In other words, if you use a 1⁄2“-long tongue, the breadboard end should be held to a 1” to 1-1⁄4” width. If the breadboard end needs to be 2-1⁄2” to 3″ wide to look right to your eye, use mortise-and-tenon construction with tenons 1-3⁄4” long at minimum.
The construction method you choose should be influenced, I think, by the use and size of the table. If the tabletop is wide, and if people are likely to lean on the end itself, the joinery between the panel and the end needs to be particularly strong. In this case, think mortise-and-tenon joint.
The simplest joint is tongue and groove. It can be through, in which case it is visible at either edge, or be blind. Depending on the size of the top, you can cut both the tongue on the tabletop and the groove in the breadboard on the table saw with a dado cutter. Any size top can be machined with a portable router and slot cutter.
Mortise and Tenon
Attaching the breadboard end with mortises and tenons is the strongest construction. The typical design features a stub tenon extending from edge to edge, with a full tenon in the center and one a couple of inches in from each edge, as shown in the drawing above. You can design a joint with only one tenon or with more than three. The mortises and tenons can be through or blind.
There’s no one “best” way to do the job. “Best” varies with the particular tabletop, with your tools, and with your experience. Here’s how I do the job.
This simple fence ensures the shoulders of your tenons align when you make a breadboard end. Stand two straight strips of medium-density fiberboard (MDF) or plywood on edge on a flat surface, and clamp scraps of the tabletop stock between them. Drive screws through the fences into one of the scraps.
Stage any cut that’s wider than a single diameter of your bit. Protect the work by clamping backup scraps (hidden by the router) to the outfeed edge. Slide the fence onto the tabletop, position and align it, then clamp it at both ends. Fit a spacer between the router and fence for the first pass; remove it to make the second pass (below). Turn the tabletop over to cut the second face.
Rout a wide rabbet across each face to make the tongue. To guide the router, make a double fence. It provides a fence across each face, and the guiding edges of those fences are in the same plane, so the tenon shoulders will line up. You slide it onto the tabletop, align one fence and clamp it. Both fences are aligned. Rout one side, turn the tabletop over and do the other side.
To stabilize the router for a wide cut, leave a full-thickness strip along the end of the tabletop. When the cut is completed, you can pop off the waste with a chisel, or simply crosscut the tabletop to remove it. (This four-pass cut is being made with the wide spacer for the first pass, the narrow spacer flat for the second and on edge for the third pass. The final pass is accomplished with the router directly against the fence.)
Lay out the tenons next. Use a marking gauge to scribe the end of the stub tenon. With a small square and a pencil, mark the edges of the full-length tenons. Cut to the lines with a jigsaw.
Use a marking gauge to scribe the edge of the stub tenon. Mark off the edges of the full tenons with a small square.
Cut the tenons with a jigsaw. Use a scrap of 1⁄2″ MDF to support the saw when you cut the edges of the tenons and saw an arc into the waste between the tenons. You can rest the saw on the tabletop to cut along the stub tenon.
Making the breadboards is next. Crosscut them 2″ or 3″ overlong; you can trim them to final length just before pinning them to the tabletop. Rout (or saw) the groove for the stub tenon first. A through groove can be produced on the table saw or the router table, but a blind one (stopped on both ends) is done most safely on the router table.
First groove an edge of each breadboard end. To lay out the mortises, fit the breadboard end onto the tenons and mark their edges on the end.
I rout the mortises in the ends with a plunge router, edge guide and a shop-made mortising jig (see issue #140 for details on the jig). Rout the center mortise slightly wider than the tenon (1⁄16″), but cut the flanking mortises wider than the tenons (1⁄8″ or more) to accommodate expansion and contraction of the tabletop.
Lay out and cut the mortises next. I transfer the margins of the actual tenons to the breadboard. For the center mortise, I’ll offset the marks about 1⁄16“, for the outer mortises 1⁄8” to 3⁄16“, depending upon the species of wood and the width of the top.
This offset allows the top to expand. I use a plunge router, edge-guide and shop-made mortising fixture to cut the mortises, but you can use a hollow-chisel mortiser.
The holes for the pins in the outside tenons must be elongated to allow the tabletop to move. If the end is to be held tight to the tenon shoulders, the elongation must be parallel to the shoulders. So use a marking gauge to scribe tangents to the drilled hole, and stay within the marks as you extend the hole.
Fit the breadboard and secure it temporarily with a couple of pipe clamps. Lay out and drill holes for the pins that will permanently secure it, one pin per tenon. I locate them about 1″ from the shoulder of the joint. Remove the breadboard end and elongate the holes in the two outside tenons. I think it’s important not to enlarge the holes, since that would allow a gap to open between the breadboard end and the tabletop. Remount the breadboard ends and drive the pins.
Fit the breadboard ends without glue (or with only the center tenon glued). Apply a couple clamps to hold the ends in place while you drive the wooden pins that secure the ends on the tabletop.
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