Measure the diameter of your corks and determine the length and width of your square trivet frame. The length and width of the inside of the frame will be equal.
Cut two boards to equal the inside measurement of the trivet. Cut the other two boards at this length plus .5 inches. Position the two longer boards on edge, parallel and spaced to equal the length of the two shorter boards. Set the two shorter boards on edge and between the first pair at a right angle. The corners are flush. Glue the boards together in this position.
Measure the length and width of the four boards and cut the plywood to this measurement using your table saw. Use the fence as your guide when cutting these boards.
Set the plywood on top of the boards so the edges are flush with the sides of the boards. Glue the plywood to the boards in this position. Your wine cork trivet frame is ready for the corks to be glued into it.