Trestle tables look like old railroad bridges: thus the name trestle table. They typically have an jamb on both sides, with a support beam connecting the two. They're not the sturdiest table in the neighborhood. The trestles are designed with aesthetics and fashion instead of functionality. If a trestle table is pushed or slid, it can weaken the trestles. The table becomes wobbly and no matter how much glue or bracing you apply, it remains unstable. One sure-fire repair is to add real legs to the table.
Remove the trestle base in one piece. Turn the table upside down. Look for four horizontal wood braces, 3/4-by-1 1/2-inches, on both sides of the trestle jambs. The braces run perpendicular to the grain of the wood on the tabletop. There are horizontal screws and vertical screws on the braces. Use a drill/driver to remove the screws from the braces. If there are metal clips or fasteners on the braces or tabletop, unscrew the screws from them and remove them.
Tap the trestle bases with a rubber mallet if they do not come off. If they still won't budge, tap a chisel under them to loosen the glue, and then remove the trestle base, including both jambs and the horizontal support beam, in one piece.
Sand smooth all four 2 1/2-by-2 1/2-by-28 1/2-inch pieces of hardwood using a hand sanding block with 100-grit sandpaper.
Apply glue to the tops of all four 2 1/2-by-2 1/2-by-28 1/2-inch hardwood pieces, or legs. Center the 3/4-by-4-by-4-inch pieces of plywood on top of each leg. Shoot two, 1 1/4-inch pin nails through each piece of plywood to secure it to the top of the leg.
Drill three holes through the plywood to penetrate down into the tops of each leg. Drill the holes 2-inches deep in a triangular pattern centered on the leg, using a 5/32-inch bit and a drill/driver. Countersink another hole in each existing hole using a 3/8-inch bit to a depth of 1/8 inch.
Insert 2-inch screws in the holes. Drive them in tight to secure the plywood to the tops of the legs.
Apply glue to the plywood pieces. Stand the legs in each corner with the plywood flush in each corner. Shoot two, 1 1/4-inch pin nails through each piece of plywood on both side of the legs. Predrill four holes through the plywood using a 5/32-inch bit. Space the holes evenly, 3/4-inch from each side of the plywood.
Insert 1 1/4-inch screws in the holes. Drive the screws in to secure the legs to the table. Stand the table upright.