A couple of weeks ago Kerry Burton brought up some questions about this issue.
Found this very interesting to investigate what the possibility's are to make such a device for own use.
I have now a temporary design of such a device for building on my lathe.
Still have to look more close to details like bearings, wearing parts and so on.
So I'm not done yet.
I made diagrams for the completion of the oval, and worked this out in a construction plan.
Used the system of a long arm plane bank for the slide movement.
The working principe of this device: excenter turns 180 degrees, means that the slide moves 30mm to the left, and the faceplate turns 90 degrees counterclockwise. So a 1/4 of the oval. A full revolution of 360 degrees of the excenter creates the 1/2 of the oval. Have to look also for other shapes of ovals.
Have the intension to build this device next year.