Here’s a safe and sound way to make long cuts with a circular saw on plywood clamped to a worktable. Cut about 12 in. into the plywood, then twist a piece of duct tape into a bow tie, with up-and-down adhesive faces. Slide it in the saw kerf and press the tape down above and under the plywood. Now as you finish the cut, the trailing end can’t curl down dangerously as you saw. Hats off to Mike Connelly for simplifying this job. Check out how to make this DIY duct tape wallet.
Often times at first glance a board looks straight and the fact that it is actually bowed or has some warping isn’t always obvious. So the trick to knowing for sure, is to hold the board up towards your face, with the other end on the ground, and look at it at a downward angle (as shown in the below photo). This method will allow you to see if it is bowing at all.