Why Did My Sofa Casters Buckle?
Issue: Issue 318
Posted Date: 1/22/2013
Recently I built a sofa and the casters legs I put on it are now buckling. I'm not too sure why. I have used pine so maybe it is too soft a wood to take the pressure? I'd really appreciate your help. It is such a shame that I may have failed at the last hurdle. - Chris Churchill
Tim Inman: Short answer: The structure is not strong enough to hold the stresses magnified by that caster design. Longer version: These casters are always a problem. They are attractive, and often seen in period antiques, especially "slipper" chairs and occasional tables. But, the "caster" provided by putting the center of the wheel so far behind the center of the weight vector (line of force) dramatically increases the torque or stress load put on the wood. To illustrate it another way, putting the center of the wheel that far behind the leg is like adding a long lever to bend that leg out of place when the weight load goes on! The chair rails or skirting pieces have probably broken out. I've been restoring furniture for decades, and I see these breaks frequently.
On newer furniture, the chair skirting is often held in place on the leg by just a couple of dowels on either side. They never hold. True mortise and tenon joints break out, too. One suggestion for a "fix" would be to go up inside the chair and install a piece of wood diagonally across the leg to reinforce the joint with triangulation. The new wood should be the same width as the skirting, and about 6-inches long. Cut 45-degree miters on the ends so you get a nice surface fit. Attach it to both pieces of the skirting with glue and screws, and put a lag screw through it in the center, that goes into the leg itself. This provides a stronger support. This cornering system is often seen in both new and older furniture.