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From the pages of The Complete Illustrated Guide to Joinery Edge Joints An introduction to the various types of edge joint, and what you need to know to make them There's no more thorough and readable guide to joinery than this new book from expert woodworker Gary Rogowski. The Complete Illustrated Guide to Joinery uses full-color, step-by-step photo essays to show you how to make every practical woodworking joint. In this excerpt from Section 14, Rogowski provides an overview of edge-joint construction.
Edge-joint uses You can use edge joints to make simple laminations, construct coopered door shapes, or create wide panels from narrow widths. You can also construct tabletops, carcase sides, and the panels that fit into frames. Edge lamination is used to band the edges of plywood or other sheet-good materials with solid wood.
Edge joinery attempts to do a very basic and yet sometimes difficult task: mating two edges together completely along their entire length. Most boards flex enough even in their width to allow you to clamp out any gaps at the ends of a board. But consider that twice as much moisture loss and gain occurs out at the end of a board through the end grain. If an edge lamination is going to fail, it will usually fail at the end of a board first. This is where a spring joint really shines. By planing in a small hollow along the length of the boards, you will need to apply pressure to close up the joint. This creates more pressure and a little bit of springback at the ends where the boards start to lose moisture first. Cut this hollow into both mating edges and then check for a sliver of light shining through the joint.
Before doing any edge lamination, get in the habit of checking some details for the best results. Arrange the boards for grain direction before joining the edges. Some woodworkers alternate heart sides up or down to minimize cupping. Others run the boards consistently heart side up or down to yield a consistent cup. Still others just choose the best-looking combination of boards. If you're going to handplane the faces after gluing, line up the grain for a consistent planing direction. Remember that there are eight possible ways to arrange two boards together for a simple edge lamination, so there are plenty of options. Mark out the face sides and which edges will be glued together. Use flat pipe or bar clamps that you can register the boards on accurately. Have them resting on a good true surface. If the clamps and work surface are flat and you keep the boards flat on the clamps, your laminations have a much better chance of coming out flat as well.
Reinforcing edge joints An edge joint mates long grain to long grain, which allows ideal gluing surface. For that reason, a glued edge joint has great strength, even without the addition of reinforcements. Tests have shown that an edge joint properly jointed and glued with modern adhesives has greater strength than the original solid wood. So why reinforce an edge joint? Reinforcements in the form of biscuits, dowels, splines, or tongues and grooves make alignment much easier. Beyond this, reinforcements provide a mechanical connection, which strengthen the joint. Without them, you must depend on the adhesive alone to hold the joint together. Splines help align edge joints and can be used decoratively. Use plywood splines or use solid-wood splines with their grain running across the groove for the best strength. It's easier to cut a spline to match the grain direction of the mating boards, but it's also easier to break it along the long grain. A tongue-and-groove joint is another effective way to join edges. The key to making a strong joint is designing and cutting it to the right proportions.
Sheet goods are invaluable in cabinet construction, but plywood edges are ugly. Although commercially available edgebanding may be a quick solution, custom edgebanding is more durable and certainly more elegant (see Edgebanding options). Making your own edgebanding allows you to match stock color, especially for unusual species. Custom edgebanding also means more design options, including profiles.
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