After thinking a long time on my first design, I found another and more simply way for building an oval turning device, so with less parts than in my first design, and also with the possibility to turn three different oval shapes..
All the rotating parts are fitted with rollerbearings, and the swivel points with nylon bearings. The device is lathe driven by using chainwheels with rollerchains. The reduction between the driven shaft and the faceplate is 1:2, so a rotation of 180 degrees of the crankshaft means a rotation of 90 degrees of the faceplate, and a translation of the faceplate to the left, this movement creates a quarter of the oval shape.
Most of the needed parts, like rollerbearings, chainwheels and other material I have in stock.
Think to start with building this device in about a couple of weeks, having still the time to think it all over, and to change something.
Thanks for looking.