Popular Woodworking 2007-04 № 161, страница 53
As you separate the chair parts, label them so you don't get them mixed up. Along with, or instead of, labeling the parts, you can lay them out in an order you understand to keep track of how they will go back together. But hot hide glue requires effort to prepare and takes practice to learn to use, so for the purpose of this article I'm assuming you will use white or yellow glue. Therefore, you will need to remove the old glue. (White glue provides more working time and still creates a bond stronger than the wood itself; I've never understood the rationale for exterior adhesives on indoor projects.) If any dowels separate from rails with their theoretically stronger side-grain-to-side-grain bonds, it's best to replace all the dowels because you can't trust any of the bonds to hold. If the dowels separate only from the perpendicular legs, you can choose to clean the dowels and the holes and avoid having to replace them. You may also have to replace some or all of the dowels. A basic rule of joinery is that wood bonds well side-grain-to-side-grain and poorly end-grain-to-end-grain or side-grain-to-end-grain. (One reason corner blocks can't be counted on to strengthen joints is that the blocks are cut on a 45° angle.) Notice that dowels inserted parallel in rails are 100 percent side-grain-to-side-grain while dowels inserted perpendicularly into legs are in contact with end grain on two sides, top and bottom. The leg side of the dowel is therefore weaker than the rail side, and dowels usually separate from the leg long before the rail. Assuming this happens with a chair you're regluing, you can choose to leave the dowels attached to the rails and hope they remain strong for as long as they do in the reglued legs. Or you can avoid taking chance s and replace them. I usually remove all dowels and replace them. But I'm an exception in the professional restoration trade. Sometimes, as with the chair I'm using for illustration, the chair will tell you which path is best. Notice (above) that some of the dowels separated from the rail rather than the leg. This indicates the bond on the rail side can't be trusted. I always choose to replace all dowels in this situation. Whatever you decide, the one thing you can't compromise on is cleaning off the old glue, including from the holes, before regluing the chair. There are two ways to do this: scrape the glue off or dissolve and wash it off. If the old glue is hide glue, it's easy to wash off using hot water. This is the best method because scraping removes some of the wood, which may reduce wood-to-wood contact. You can also break down white and yellow glue by soaking in hot water. You can add vinegar to the water to accelerate the process a little. Other adhesives will have to be scraped. Do the best you can to remove as much of the glue and as little of the wood as possible. Replacing Dowels: First, Out With the Old Replacing dowels requires removing the old dowels from the joints first. Sometimes you can strike the ends of the dowels with a metal hammer or twist them with pliers to break glue bonds. With the dowels loose, twist and pull them out using pliers. If the dowels won't break loose and you still want to remove them, follow this procedure. With the part clamped in a vise, saw off the dowel about 1//16" above the surface. Then, using a brad-point drill bit 1//16" smaller in diameter than that of the dowel, drill down the center of the dowel until you reach the air pocket at popularwoodworking.com I 67 |
