I cut my presensitized PCBs down to size with rulers and a utility knife when I need a custom PCB.
I noticed every time I cut one, the cut is always clean, but the copper on the board at the same edge as the cut I made is uneven. In fact it curls up and that makes PCB development difficult because the board isn't 100% flat to the glass when exposing it.
Here's a picture illustrating what I am talking about:
Currently, I use sandpaper to try to sand the excess copper so the board is as flat as possible but it wears the sandpaper fast.
Sometimes I use the utility knife at a 45 degree angle on the edge. While this often removes the curl, it also removes at least a good 30mils from the copper.
What's the best way to remove the curl without wasting a lot of PCB material or wasting any other materials? I don't think sandpaper is up to the task.