Leisure World of Maryland
A: If you were dealing with structural joints — for example, ones that were holding legs or the back in place — screws alone would probably not be enough to keep the chair from becoming wobbly over time. Wood expands and contracts as temperature and humidity shift. That unavoidable fact, plus the stresses put on chairs as people scoot in and out or rock back and forth, can break the thin bits of wood that alternate with the metal threads in a screw hole. Metal-to-metal connections, such as bolts with nuts or threaded inserts into metal fasteners, are far more durable.
But in this case, the screws are just holding the base of the seat in place. When people sit down, the seat might shift, but it won’t fall out, even if the screws aren’t completely tight. The screws go into corner blocks, which are typically glued to the chair framing — as in your chair, judging from the picture you sent. If the holes in the corner blocks are oversize, that’s not a problem. What matters is that the screws grip to the wood in the seat.
In most upholstered chairs, the seat is plywood, probably ½ - to ¾ -inch thick. The thin layers of wood in plywood can easily crumble if screws are inserted and taken out multiple times. Plus, if the chair was ever recovered over the old upholstery, or if replacement upholstery was thicker than the initial covering, the original screws might not seat as deeply as they once did, causing the screws to spin rather than tighten.
You have a few options for fixing this.
It might be enough to replace the screws with ones that are a little thicker or longer. Just ensure the replacement screws don’t protrude past the corner blocks more than the thickness of the plywood.
Rather than making the screws bigger, you can also try to narrow the opening where the screws fit. There is no need to change the holes in the corner blocks; as long as the holes are narrower than the screw heads, this part of the screw holes can be oversize. What matters is that the hole diameter in the seat is narrow enough for the screws to grip there. Screws are like miniature clamps, with the back of the head serving as one side of the clamp and the threads gripping into the piece being fastened to the other end. The screw shaft and the wood in between play no role.
One of the simplest options for making an existing screw hole narrower is a trick that trim carpenters often resort to when they need to install doors where hinge screws have stripped out: Squirt a little wood glue in the holes, then stuff in slivers of wood. Wooden toothpicks work well. Aim these in point first; wait for the glue to dry, then trim flush with a utility knife or chisel. Depending on how tightly you pack the slivers, you may need to pre-drill before reinstalling the screws.
Or, you can fill the holes and redrill. Most wood fillers aren’t suitable, but you can use epoxy, such as KwikWood Epoxy Putty ($4.98 for a one-ounce package at Home Depot). Pack it into the hole; it doesn’t work to just skim the epoxy over the top of the hole. For filling deep holes, some people use syringes, such as those sold at animal-feed stores. But a chair seat is thin enough that you could probably improvise by breaking off a round toothpick and using a blunt end to tamp with. Epoxy dries hard and doesn’t shrink or pull away from wood. KwikWood says its product has a 15- to 25-minute work life and can be drilled into after one hour.
Another solution — which might be more than you need for this purpose, but it could be handy in other situations — is to treat the stripped hole as if it were a hole into crumbly drywall.
Screw-It-Again inserts ($13.99 for a package of 10 on Amazon) look similar to the plastic sleeves used to fasten screws to drywall. The inserts for wood have threads on the outside that grip into the stripped hole; each insert also has an interior hole to hold the screw. You just use a screwdriver to twist an insert into a hole until the insert bottoms out. Tilting the screwdriver sideways then snaps off the fastener flush with the surface. Depending on the hole diameter and where you snap off the excess length, a single insert might be enough to fix several stripped holes.
Other companies offer variations on ways to plug stripped holes, so screws can grip again. Woodmate, for example, makes the Mr. Grip Screw Hole Repair Kit ($4.60 on Amazon).
The final option for fixing the stripped holes: Replace the seat, which is probably nothing more than a small piece of plywood.
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