Retired Engineer Built A Roller Coaster For His Grandkids DIY October 6, 2023 | By Andrew S Critical Cupping Source As with any rail project, the first step was to design a track that would keep the car safe without slowing it down. He devised a machine that would cut cupped edges for wooden boards, fitting them snugly into a rounded rail line. BACK3 of 40NEXT ➔