I like to put nice radius curves on the corners of my plywood projects. I could use a compass but this is a lot easier:
I use paint can lids. Not a perfect range of sizes, but I have four available.
Step 1: Line Up the Corner
So when I want to round off a corner I pick a size, line it up on the corner. Then I use a pencil or maker to draw around the lid.
Step 2: Radius Line Finished
So there you have it, a quick way to draw a radius. My next step would be to cut the plywood off with the saber saw.
Step 3: Last Step - Clean Up and Store
And no job is really finished until you clean up and store your tools. For these I punched holes in the lids so I can hang them all on a nail. This is over a door where they are out of the way.
I also marked each one with its diameter, it is just nice to know.
Good luck, hope you find this useful!