Camwheel for sewing machine OpenScad

At 'gered gereedschap' in Groningen we fix machinery tools and sewing machines for a second life in developing countries. This exposes sometimes design flaws of machines made many decennia earlier. While sewing machines made before the fifties are generally virtually indestructable because all parts are made from sturdy metal, later machines are built using plastic for gears and camwheels. An old Husqvarna machine was given to us for refurbishment. It contained a plastic camwheel to define the different stitches. The plastic was injection moulded on an iron center with a diameter of 3 cm. The plastic was between 3 and 5 mm thick and contained 7 different layers for the different stitches. The camwheel was made from PVC and due to ageing and different expansion characteristics of metal and plastic it was broken with a 0.5 mm gap and therefore not anymore stable fixed to the metal core. Usually we discard these machines because a new camwheel is not easily available and if available the