How do I cut a beveled fence post cap on already installed fence posts?
I use 2 large C clamps to hold a board in place. You can screw a guide board to the post if you don't have large C clamps. Then use a circular saw with the blade adjusted to the angle you want. By using a board the cut will be straight. Then move the board to the next side and repeat. There will be small screw holes in the post if you use screws but I have done this in a pinch when I did not have my clamps handy.