In this video, This Old House general contractor Tom Silva and host Kevin O'Connor show how to make precise and perfectly straight cuts with a portable circular saw.
- Mark the cut line onto the workpiece, then measure the distance from the circular saw blade to the edge of the saw shoe. That will be the offset dimension.
- Measure over from the cut line the offset dimension and make a second mark.
- Clamp a 6-inch-wide piece of ¼-inch plywood to the workpiece on the second offset mark. Run the saw along the edge of the plywood to produce straight cut.
- Use a straightedge clamp as a saw guide. Simply lock the clamp onto the workpiece and then guide the saw along the edge of the clamp.
- Make a straightedge guide from two 48-inch-long pieces of ¼-inch plywood. Rip the base piece about 12 inches wide and make the fence 3 inches wide.
- Glue the fence to the base, positioning it ½ inch beyond the saw's offset dimension.
- Guide the circular saw along the fence to trim the base to the proper width. Repeat to trim the other side of the base, just be sure to guide the opposite edge of the saw shoe against the fence.
- When using the straightedge guide, simply clamp its edge directly on the cut line. There's no need to measure for the offset. Then guide the saw along the fence to make an accurate, perfectly straight cut.