How to Put Plywood Tread on Winder Stairs

Locate the outside edge of the lower triangle step. For a winder stair that turns right, this will be the left corner, and vice versa. Use a square to draw a line, in line with the face of the step's riser, up the wall to a point even with the top of the wedge shaped corner tread.

Measure from the corner of the wall above the wedge shaped step to the line. Cut a square of cardboard with a side of the same dimension. For example, if the distance from the corner to the line is 20 inches, cut a 20-inch square.

Make an X in one corner and align this cardboard template so that the X represents the corner of the wall above the wedge shaped middle winder. Position the X on the side of the square away from you and on the right or left, depending on the turn of your stairs. If the stair turns left, this will be on the right, and vice versa.

Measure from the corner marked with the X to the front edge. Make a mark exactly in the middle of that side of the square. Measure from the marked corner along the side of the square away from you and mark the center of that side as well. Use a straight edge to mark straight lines from the two center marks to the corner opposite the X. Mark the edge of each section that represents the front edge of the step.

Cut along the lines with a utility knife to separate the template into three sections. Lay the cardboard pieces out on a sheet of 3/4-inch plywood. Outline the templates on the plywood. Locate the marked front edge of each step and draw a line parallel to the front edge line, extending the template by 3/4 inch. Cut the three steps out, including the extension, with a jigsaw.

Install a 1/4-inch round over bit with a bearing into your router and set the depth of the bit so that the bearing will ride in the center of the plywood edge on the stair tread pieces. Run the router along one face of the extended front edge of each tread. Flip the pieces over and run the router along the remaining face to create a rounded front edge.

Sand the treads with 120-grit sandpaper. Position the plywood treads on each step and nail into the frame below with 2-inch nails in a finish nailer. Use one nail every 8 inches.