Attaching a top to its base is a critical aspect of table design and construction. Regardless of the method you choose, it should meet the following criteria: The top must be firmly attached to the base; the top must remain flat; a solid-wood top must be allowed to move seasonally; and the attachment method shouldn’t compromise the design of the table or complicate its construction. I’ll describe four ways of attaching a tabletop that meet these requirements, along with the reasoning behind each method.
The most important factor to consider when deciding how to attach a tabletop is wood movement. We all know that solid wood moves seasonally across the grain. It’s a fact; you can’t do anything to stop it. In the summer, a board will expand across its width because of an increase in humidity. During cold months in a dry, heated room, the same board will shrink and become narrower. If no allowance is made to control or direct this seasonal movement, a tabletop might buckle, or worse, crack and split.
When calculating how much a board will move, I usually allow from1⁄8 in. to 3⁄16 in. for every 12 in. of width. Therefore, I would anticipate that a 42-in.-wide tabletop might move about 1⁄2 in. overall. This is only a general guide, and certain factors must be taken into account. For instance, in parts of the country with low humidity, wood movement might be minimal.
Another factor is the type of wood you’re using: Cherry moves less than white oak but more than mahogany, while flatsawn wood moves more than quartersawn. For more on this subject, read Understanding Wood by R. Bruce Hoadley (The Taunton Press, 2000).
Once you accept that the tabletop will move, you can control or direct this movement so that it doesn’t disrupt how the table works or looks (see drawings, below). For a freestanding table with a uniform overhang, I anchor the top to the base at the center of the end aprons. That way, any cross-grain movement will occur evenly along each long-grain side. On a demilune (half-round) table, I pin the back edge of the top, which typically is placed against a wall. Conversely, on a writing table I might fix the top along the front of the table so that movement occurs toward the rear.
For this article, I have illustrated four methods of securing a table-top. The methods are listed by ease of installation, starting with the simplest. The hardware for two of the methods can be purchased relatively cheaply from hardware catalogs, while the rest can be made from shop scrap. This is a low-budget process.
While you cannot prevent a solid-wood tabletop from moving seasonally, you can direct this movement so that it doesn’t disrupt the looks or the use of the table. Below are examples of how to secure the tabletop to the frame to control expansion and contraction.
This is probably the oldest way of attaching a tabletop. Drill a 1/2-in. flat-bottomed pocket hole at a 10° angle into the apron. Then drill a smaller pilot hole (to accommodate the shank of a #8 wood screw) into the center of the pocket hole. Common on antique furniture, pocket holes make no allowance for wood movement, which may explain the number of cracked and split tabletops.
On small solid-wood tops (up to 9 in.) or veneered plywood tops, pocket holes can be the only attachment method. On larger pieces, they should be limited to areas needing restricted movement.
These clips, also known as S-shaped clips or simply as tabletop fasteners, are probably the easiest and quickest method for attaching tabletops. They fit into a groove or slots cut on the inside face of the apron.
The grooves must be cut before the base is assembled. The easiest method is to use a tablesaw. The clips are installed after the base has been assembled. Place one end of the clip into the groove and screw the other end into the underside of the tabletop. Because the groove runs the length of the apron, any number of clips can be used. This method nicely accommodates any cross-grain wood movement whether the clips are parallel or perpendicular to the tabletop’s grain: the clips on the end aprons move along the groove as the wood moves, while the clips on the front and back move in and out of the groove.
Another way to install the clips is to cut slots in the apron using a biscuit joiner. This method is quick and easy, and it can be done after the base of the table has been glued up.
Also known as a desktop or figure-eight clip, this unobtrusive fastener requires only a shallow flat-bottomed recess in the top edge of the apron. The diameter of the recess should accommodate that of the clip, but the recess should be drilled to place the center of the clip past the edge of the apron. t his will let the clip pivot slightly, allowing for cross-grain wood movement.
For large tabletops, you can increase the clip’s ability to move side to side by chiseling away a little of the apron on both sides of the clip. However, because the clips do not handle wood movement perpendicular to the apron very well, they are best confined to end aprons. Like the metal table clips (above), these fasteners should be relegated to casual, day-to-day furniture pieces.
This type of fastener is made from project leftovers. These blocks are attached to the tabletop with screws and have projecting tongues that engage corresponding grooves cut into the apron. The apron grooves are slightly larger than the width of the blocks, allowing for movement and preventing the tabletop from splitting.
By carefully laying out the placement of the blocks and milling properly sized grooves, a more tailored and carefully crafted appearance is achieved. The best way to cut the grooves is with a router guided by a fence bearing on the apron. Properly spaced, tongue-and-groove blocks work very well for all sizes of tabletops.
Make sure that the distance (a) is fractionally greater than (b) to ensure that the tabletop is tightly attached to the frame but still free to move.