Compensating for Movement

This is an excerpt from “With the Grain” by Christian Becksvoort. 

With a background in forestry, wood technology, furniture construction and restoration and many decades of joinery, I’ve developed a system of case construction that fully allows solid-wood panels to move throughout the seasons. None of it is entirely original, most is borrowed from antique builders, some is common sense and a minute portion (expansion washers, for example) is my solution to age-old problems. No case I’ve ever restored utilized all of the described techniques, so this is more or less a compilation of the best joinery I’ve had the privilege to restore and learn from.

Once the panels are glued, sanded and cut to size, construction can begin. Edges need to be cut parallel and ends perfectly square. The best sides should be oriented toward the outside and so marked. Then rabbets are cut on the inner back edges to accept the case back. The joints to attach the top to the sides can be a screwed butt joint, single or double rabbet joint, through- or half-blind dovetails, or even a splined miter. If the case is to sit on an applied bracket base, the same joinery can be used for the bottom.

Before gluing the top to the sides, a bit of planning is in order. This is the time to cut matching dados and grooves for any interior dividers, shelves, or web frames to support drawers. If the case side runs all the way to the floor, the bottom is usually dadoed or secured with sliding dovetails 4″-6″ (10-15 cm) from the floor. In either instance, glue or screw blocks (shown below) should be used underneath to strengthen the joint. Once all the interior joinery is cut, the four sides of the case can be glued and assembled.

A web frame (shown at top) consists of four or five narrow pieces dovetailed and mortised and tenoned together to support drawers. Although extra work, they do save both material and considerable weight. The preferred method of building web frames to give maximum support to the drawers, yet allow the cabinet sides to fully expand and contract, is as follows:

The horizontal side-to-side frame members have dovetails on both ends and mortises on the inside edges, right next to the dovetails. The front-to-back drawer runners are tenoned on both ends. The shoulder-to-shoulder dimension of the runners should be slightly less than the distance between the front and back frame members. On the case interior, there should be four short dovetail slots (two per side, to accept the side-to-side frame members), connected by a shallow dado, roughly 1/8″ deep (.32 cm).

To assemble: The front side–to-side piece is glued first. When the dovetails bottom out, the front of the case and the just-installed member should be flush. Next, glue is spread into the front mortises. Then the drawer runners are inserted into the side dados and the front tenon is slid into the front mortise, both left and right runners. Lastly, the back side-to-side frame member is glued into the dovetail slots. The back mortise and tenon are not glued. This allows the joint to telescope in and out, as the case sides expand and contract. The gap between the runners and the back frame member could be as much as 1/8″ to 1/4″ (.32 to .64 cm) if the panels are close to 14 percent MC, and will most likely shrink; smaller if the side panels are closer to 6 percent MC and expansion is anticipated.

A final word about case bottoms: If a solid wood bottom is used, glue blocks should be installed. If, however, a web frame is preferred to save weight, then a dust panel should be incorporated to seal the bottom. Grooves should be cut on the inner portion of the web frame, and a panel fitted during assembly to seal out dust and dirt. Generally speaking, dust panels are not required on other interior web frames.

At each step of construction the case should be checked for squareness. Small errors tend to accumulate if not rectified from the start. Before fitting the back, the case should be carefully checked to be sure it is square. Assuming that both sides are identical in length, and the top and bottom widths are the same, then simple diagonal measurements will point out any errors. Measure from the top left corner of the case to the bottom right, then from the top right to the bottom-left corner. If the two measurements do not match, a clamp between the two longer corners should pull it into position. Re-check the measurements before proceeding to build and install the back of the case.

— Meghan B.