How do I make a perfect disc from thin plastic sheet

The question is how does one make a perfect disc shape from plastic sheet ?

I have thought and tried using sicssors but not too accurate,

So thinking caps on, what tools do you folks suggest?.The template for the circle can be a compass but I just need the neatness of the cut.

Reason for this question,i dont like the wheel centers of  Revell's  Austin Healy so i an trying to find a way of fabricating something for the wheel centers without resorting to aftermarket bits.More satisfaction that way?

Source: http://cs.scaleautomag.com/SCACS/forums/thread/977293.aspx

Julian Bailey Mauro Baldi Bobby Ball Marcel Balsa