Steps:1. Use the hammer and pry bars to remove nails from plywood patch and pry the patch up (figure A). For really stubborn nails, use the nail puller.
2. You'll probably need to trim the original boards to create a nice, straight edge for your patch. Nail a board into the floor to serve as a guide and adjust the circular saw blade so it cuts just through the floor and not through the joist below (figure B). Remember to always wear proper eye protection and a dust mask when working with power tools.
3. Decide on a strategy for replacing the patch. Instead of patching along the straight edge, weave the old boards in with the new so the patch blends in better when the floor is refinished (figure C). Decide which boards to leave and which ones you'll need to remove.
4. Mark a line for the longer replacement boards so the ends fall in the center of a floor joist (figure D).
5. If necessary, pry old boards away from sides of opening. Remove old boards for the weave by drilling into the ends with the paddle bit to make starter holes for the circular saw (figure E). Use a circular saw to rip down the length of the board, then pry out pieces until the section of board is removed. Continue until enough old boards are removed for you to weave in the new boards.
6. Use a chisel to clean out the area around the cuts.
7. Measure for new boards and cut to length. Since you're making a weave, you'll have long and short boards. Trim the lips from one side of the longer boards so the groove will fit over the tongue of the existing tongue-and-groove boards (figure F).
8. Drill pilot holes through the tongue and attach the new boards to the floor joists using nails (figure G). Use a nail set to sink the nail below the surface so the tongue-and-groove boards will fit together. As you work along the floor, also nail the ends of the new boards to the joist.
9. Fill any gaps with wood putty. Condition and stain floor as desired.