Checking and repairing the frame of a chair will stop the wobbles.

Checking and repairing the frame is a crucial part of upholstery. Most broken frames can be mended at home, but you may also take the frame to a cabinet-maker or upholsterer to repair.

You'll need
Bent ripping chisel
Wooden and/or rubber mallet
Medium-size hammer
Medium-size chisel
Coarse abrasive paper
PVA wood adhesive
Damp cloth
Replacement dowel (if necessary)
Dowel-sized drill bit and electric drill (if necessary)
Clamps (for regluing if necessary)

Step 1
Checking the joints
Most joints in modern furniture consist of two or three wooden dowels glued together with PVA wood adhesive. Tongue-and-groove joints or plain, glued joints held by staples or screws are less common. All come apart in the same way.

Pull the timber rails in various directions and, with your hand only, try to part the joint. If you can see or feel any movement at the joint, it is loose and will need repair. Proceed with caution as some joints have slight movement but aren't ready to come apart. If you try to remove them with undue force, the dowel will probably break or split the timber rail or the timber rail or leg may even snap in half.

Corner blocks
Many chair frames have a reinforcing corner block that must be removed before regluing the joints. Most corner blocks are glued and nailed, but if there are screws holding the block, unscrew them first.

Step 2
Mark the top of the corner block and the nearby timber rail with a number to identify its position.

Step 3
Place the flat point of the ripping chisel where one side of the block meets the rail and tap the end of the chisel with a wooden mallet to force the block away from the rail. Once the chisel is in as far as the bend, lever forwards and downwards to remove the block. If the block is stubborn when you lever it, remove your chisel or the chisel may snap. Hit the block hard with a mallet in a downward motion to detach it.

Step 4
Repairing the joints
Place the chair on a workbench so the rail to be removed is horizontal but not resting on the bench. Hold the adjoining rail in one hand and tap the horizontal rail with a rubber mallet downwards as close to the joint as possible. You may have to tap very firmly a few times before the joint parts. If the joint doesn't part after a few taps, do not proceed as the joint is not ready to come apart.

Step 5
Mark the joint so you will know where to reglue it. Sand or chisel off the old adhesive so that there is a flat end on the timber rail, with the clean dowels pointing out.

Step 6
Replacing broken dowels
If a broken dowel is still in the timber rail, chisel the dowel flat so you have a level surface to drill on. Drill out the old dowel cautiously, making sure you don't drill right through the timber rail (a very easy mistake to make). Place masking tape on the drill bit to mark the depth.

Step 7
Half fill the dowel holes on one side of the joint with PVA wood adhesive. Put in the new dowels and tap them in with a hammer. Clean excess adhesive with a damp cloth.
Place the flat point of the ripping chisel between the corner block and timber rail.

Step 8
Repairing tongue-and-groove joints
If you can part a tongue-and-goove joint without breaking the tongue, remove the old adhesive and reglue the joint with PVA wood adhesive applied liberally. If the wooden tongue does break, chisel the surface flat and drill holes for dowels to replace the failed joint.

Step 9
Clamping
Fill the remaining dowel holes with PVA wood adhesive so that the holes are about half to three-quarters full. Press the joints together by hand, wriggling them slightly to ease them into place. You do not have to push the joint together completely because the clamps will do that.

Step 10
Place the project in the correct, upright position. Set the clamps on the joints and tighten each one as you position it. Replace any corner blocks. Wipe off excess adhesive and place the reglued and clamped project on a flat surface so that it will remain square to the floor once the adhesive has dried.

Source:Upholstery Basics & Repairs (Murdoch Books)