Steps:1. Measure the length and width of the hole (figure A). Cut the pieces so that the opening in the new frame is slightly smaller than the opening in the ceiling. The frame will cover the rough edges of the opening, making for a neater appearance.
2. Set the miter saw to make exact 45-degree angle cuts so the frame is nice and square. After cutting one lengthwise piece, use it as a template to mark for the cut for the second piece. Do the same with the width pieces (figure B).
3. Align all the pieces on a scrap piece of plywood and apply glue to the joints.
4. Use clamps to hold the frame securely, drill pilot holes for the screws and drive screws into corners (figure C). Use low profile screws and a counter-sinking drill bit for a more finished appearance.
5. Now cut the removable panel for the interior of the frame. Install the frame to cover the opening. To make things easier, pre-drill holes at each corner and partially install the screws before lifting the frame into place (figure D).