Don’t know if this is commonly known, but looking around the internet it doesn’t seem that way so I thought it was worth a video. Very simple, quick and accurate method for making router templates. Quite long video but first 2 minutes describes the method well. This method can be used for everything from small tasks like recessing hinges to larger things like shaping furniture pieces after glue up. Steps and angles are easily achieved, illustrated with the arrow shape in the very short step by step picture series.

https://youtu.be/lGvkXGrewfU