Popular Woodworking 2003-08 № 135, страница 26
Make Accurate Half-lap Joints
Photos by the author
The versatile half-lap is easy to cut with 2 jigs and a router.
A half-lap joint is strong, versatile and easy to cut. You simply cut recesses in both mating pieces, then nest them together, forming an X, L or T.
Half-laps can be used for all sorts of flat frames. Doors, for example, but also face frames, web frames and picture frames. An intermediate rail half-lapped to the stiles "looks" right because it visually abuts the stile (the way a mortise-and-tenon joint would) rather than crossing it (the way a bridle joint would). On the other hand, a rectangle of end grain is exposed in assembled end laps and T-laps (see diagrams on page 26), which can be regarded as unsightly.
The half-lap can be used in post-and-rail constructions to join rails or aprons to legs. You usually see this joint in worktables rather than fine furniture. But even in the most traditional table construction, the half-lap is used where stretchers cross (a cross-lap).
From a practical perspective, the half-lap enjoys an advantage over the mortise-and-tenon joint in that one tool setup can suffice for both parts of the joint. (There's more than one way to cut the joint, of course, and some do require two setups, as we'll see.) You can join parts at angles quite easily. The joint accommodates curved parts, too. You can join curved pieces, or you can shape the half-lapped frame after it's assembled.
Despite its simplicity, this joint is strong if properly made. The shoulder(s) resist twisting and there is plenty of gluing surface.
But be wary of using half-laps on wide boards. Wood movement can break the joint, so confine the joinery to members no more than 3" to 31/2" wide.
You can cut half-laps using several different power tools. Let the job suggest the tool to use and the way to use it, too.
On the Router Table
Everyone has favorite approaches, and mine involves the router. I cut end-laps on the router table using a lapping sled I originally made for tenoning. This shop-made device looks like a T-square on steroids (see the drawing at right). The stout fence is long enough to extend from the tabletop edge to well beyond the bit. The shoe rides along the edge of the tabletop. An adjustable stop clamps to the fence to control the length of the cut.
Construction is simple, but pay attention to the details. The fence must be square to the shoe. The edge of the fence must be perpendicular to the tabletop. The adjustable stop also needs to be square to the fence. If any of these is off, you won't get consistently sized, square-shouldered laps.
by Bill Hylton
Bill Hylton makes noise, dirt and the occasional piece
of furniture in his basement workshop. His book "Chests of Drawers" (The Taunton Press) shows both his shop and his handiwork.
What bit to use? Well, a straight bit is the obvious choice, and it will work fine. I use what's variously called a planer, mortising or bottom-cleaning bit. The several bits I have range in diameter from 3/4" to 11/2 ", and the vertical-cutting edges range from ^V to 78". The bit is designed to clear a wide, smooth recess. Perfect for laps!
The first time you use the lapping sled you'll cut into the fence. This cut is what you use to position the stop for the length of lap you want. Measure from the shoulder of the cut (include the cut itself in the measurement, of course). The stop prevents you from making a cut that's too long.
Cutting a half-lap on the router table is fast and accurate using a lapping sled to guide the work and a large-diameter mortising bit to cut it. The guide references the edge of the tabletop and a stop sets the length of the cut.
24 Popular Woodworking August 2003