Clamping can be difficult on objects that do not have square corners or flat surfaces. Fortunately, there are clamps for almost every purpose ranging from nylon to steel. If you've got chairs with loose rungs, you may need to use special clamps or methods. Other options for clamping techniques include adding materials to the clamp or joint to assist the clamp.
Chair rungs are notorious for loosening over time depending on the type of construction. Constant pressure on contact points loosens glue, causing dowels, rungs or tenons to pull loose. This causes the chair to sag, squeak or fall apart. Sometimes glue crystallizes and becomes worthless -- especially hide glue used on very old chairs -- causing the same effect. For clamps to work properly, glue must be added to all loose joints. Before clamping, pry or pull chair joints apart slightly and add glue. If you can't get enough glue into the joint, drill a small hole in it and inject some glue. It's imperative that glue penetrate as far as possible into any loose rung joints before clamping. Woodworking glue typically bonds within one hour, but it's best to let it dry overnight.
Strap clamps are among the most efficient ways to clamp chair rungs. This type of clamp is a long nylon strap that tightens. They are particularly useful on objects that need equal pressure from all sides. Begin by applying the glue. Wrap the chair around all four legs with as many strap clamps as needed, two or three is usually sufficient. There's a metal bracket that pulls one side of the strap taut when tightened with a 1/2-inch wrench. It applies equal pressure around the perimeter of the chair to force chair rungs back where they belong. Continue tightening the clamps until glue oozes out from all the joints.
Use bar clamps for individual chair rungs. There are several types. Use large 3/4-inch pipe clamps for the most pressure. They're heavy and tough. Don't apply too much pressure with this type of clamp or you may break the chair. Place the jaws on either side of the leg and tighten until glue oozes out. This type of clamp is typically longer and will reach from side to side on any chair. For shorter individual rungs use hand clamps. This type of clamp is a small rectangular bar typically about 18 inches in length with a wooden handle. Use them for smaller chair rugs or where large bar clamps will not fit.
Sometimes bar clamp jaws won't fit on round chair legs or rungs. If this is the case, use a band saw or jigsaw to cut some small square blocks of wood with a custom curve on one side that fits over the leg. Use the block between the jaws of the clamp and the chair rung. The front of the curve on the block fits the leg and provides a square back for the jaws of the clamp. If the block slips or won't stay in place, glue some sandpaper to both sides to prevent it from slipping when you use it.
Dowels, Screws, Wedges
Even the best chair rungs fail if they're damaged, shrunk or the hole they penetrate has become stripped or too large for the dowel, rung, or tenon on the end of the rung. For the best results when clamping add additional dowels, wedges or even screws to the joint. Drill through the joints of larger chairs at an angle using a 1/2-inch drill bit. Use 3/8-inch or 1/4-inch dowels if the legs are smaller than about 1-1/2 inches in diameter. Inject glue into the hole and pound an appropriate sized dowel into the hole. When it's dry, trim off both ends flush with a chisel. You can also drill and place a screw parallel to the rung directly through the leg from the opposite side to pull the rung forward into the leg. Other options include adding small wedges to the joints with glue. Pound them in securely while you have clamps in place. Trim them off when the glue is dry. Use a stain marker to color the trimmed ends.
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