Nicolas, as everyone knows, Bj and me are great friends but I have to say that he has gone overboard on this one. These two shots make it clear, the whole demo took no more than 10 minutes including finding and cutting on the radial arm saw a piece of Perspex, fitting the cutter into the router and slapping some paint in the line followed by a couple of wipes with a tissue to remove surplus paint. I'm sure you have a router table and 90* cutter but possibly not a Dremel set-up.
Nothing but heaven itself is better than a friend who is really a friend. - Plautus