Popular Woodworking 2006-10 № 157, страница 67
Power-tool Joinery Breadboard Ends Keep Tops Flat This traditional joint ensures the only cup on your tabletop will have coffee in it. Tongue & groove Scale width of breadboard end to length of tongue.Awide breadboard end overstresses a short tongue. Round hole in breadboard end keeps pin fixed Blind tongue & groove For narrow breadboard ends, a tongue-and-groove joint works well. If the breadboard end is wider, adding mortise-and-tenon joints will add strength. The breadboard end is a traditional device for preventing a broad panel such as a tabletop from cupping. It is a narrow strip of wood that runs across the end of the main panel. Obviously, it must be attached in a way that allows the panel to expand and contract. But it also must be attached in a way that won't allow the panel to cup without forcing the strip to bow. This means there's got to be some form of interlock. You should be aware of the aesthetic. The breadboard's length won't vary, but the width of the panel will. It may turn out that the only time the two dimensions match is when you construct the tabletop. Thereafter, you'll have an endlessly varying difference. Get used to it. (If you want the look but can't accept this quirk, use plywood for the panel and glue on the breadboard end!) There are quite a few ways to attach a breadboard end. The drawing at right shows several that are particularly good if your intent is to keep the top flat. In assembling any of these joints, glue is used sparingly, if at all. Most often, wooden pins are used to lock the breadboard, so it can't pop off. A single pin in a round hole at the center secures the breadboard but allows the top to expand and contract. If pins are added anywhere else along the joint, the holes for them in the tabletop must be elongated to allow for seasonal wood movement. Remember, the top itself will expand and contract, but the length of the breadboard won't change. Establish the Proper Size The width of the breadboard end and the length of the tongue, tail or tenon need to by Bill Hylton Bill is the author of several books about furniture construction and router operations. When he isn't writing about woodworking, he's doing it in his home shop in Kempton, Pennsylvania. be in good proportion. A wide end multiplies the stresses placed on the joint. I think a good rule of thumb is to make the end no more than to 3/4" wider than the longest element of the joint. In other words, ifyou use a ^"-long tongue, the breadboard end should be held to a 1" to 1V4" width. If the breadboard end needs to be 2V2" to 3" wide to look right to your eye, use mortise-and-tenon construction with tenons 13/4" long at minimum. The construction method you choose should be influenced, I think, by the use and size of the table. If the tabletop is wide, and if people are likely to lean on the end itself, the joinery between the panel and the end needs to be particularly strong. In this case, think mortise-and-tenon joint. The simplest joint is tongue and groove. It can be through, in which case it is visible at either edge, or be blind. I wrote about tongue- 78 Popular Woodworking October 2006 |
