Rule Joints: by Hand & by Power

No matter how you cut them, understand their  subtleties to make a smooth-moving joint.

By Willard Anderson
Pages 48-53

The rule joint is elegant in its apparent simplicity and is a classic element of fine furniture. Much of what has been written on rule joints – or table joints as they’re often called – is from the power-tool perspective. While there’s nothing wrong with cutting this joint using power tools – a process I’ll discuss later – the way to truly learn about this joint is to cut it by hand using layout techniques and tools that craftsmen of the 18th and 19th century used. Once you understand the subtleties of this joint, you’ll be able to achieve better results no matter how you cut them.

What is a Rule Joint?
The rule joint gets its name from its similarity to the brass joint in folding rules. With a rule joint, the round portion of the joint provides support for the drop leaf and, when the drop leaf is lowered, eliminates the unsightly gap between the drop leaf and the tabletop. The joint is composed of a fillet at the top, a quarter-round profile on the tabletop side of the joint, a mating cove and a land on the drop-leaf side (see the illustration at right on the next page).

The hinge for this joint is unique in that it is mounted upside down (so that the barrel is buried in the workpiece) and set flush in a mortise on the underside of the tabletop. In its down position, the drop leaf rests evenly with the height of the land. The observer sees only the fillets and the barrel of the joint, but no evidence of the hinge or the hinge mortise. For the joint to operate smoothly, the hinge has to be located precisely.

Table Joint Planes
Joinery planes usually cut grooved joints (tongue-and-groove, dado, rabbet etc.), and moulding planes are generally used for decorative profiles. While table joint planes could be classed as joinery planes, they look like moulding planes. One member of a table joint pair is used to cut the profile on the tabletop (the round) and the other cuts the mating profile on the drop leaf (the hollow or cove). Table joint planes were manufactured in matched pairs but sets have often been separated over the years and they are not easy to find.

The most obvious characteristic of table joint planes is that they cut a 90°, or quarter-round, profile. In contrast, hollow and round planes cut a 60° profile (equivalent to the segment of the circle on which the profile is based). Almost every table joint plane I have seen cuts a 3⁄8″ arc or round. Any pair of these will cut rule joints on stock ranging from about 1⁄2″ to 1″ thick – the difference in thickness is made up by the height of the fillet. With any of these planes, the fence of the plane references off the underside of the stock.

Blog: Get more information on hinge placement and how it affects the joint.
Video: Episode 3203 (Table Joints Rule!) of “The Woodwright’s Shop” features Willard Anderson and will air later this year.
Blog: Discover more good resources for drop-leaf hinges in many finishes and price ranges.

From the August 2012 issue #198
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Popular Woodworking Magazine August 2012 Cover