This is a workshop hack video currently gaining steam on YouTube (about 1.7 million views and counting). It’s from the SeeJaneDrill channel, where host Leah demonstrates the “ticking stick” method of duplicating an irregular shape:
Leah’s method of using the stick is simple enough, and perfect for duplicating a shape that has straight lines. But a couple of years ago I learned that this stick, with a different method, could also be used to precisely copy an irregular, organic shape. Christopher Schwarz–who now writes “The Anarchist Designer” column for us–demonstrating this method over at Popular Woodworking.
Click here to see how he got that seat to fit perfectly inside that hollowed out trunk.
https://www.core77.com/posts/91426/Workshop-Hack-How-to-Use-a-Ticking-Stick-to-Duplicate-Both-Rectilinear-and-Organic-Shapes-Precisely