With each slice taken off the curve should start to take on its shape. When you get down to the last small portions use a vry sharp knife and the flat edge of the blade to finish.

The same technique can be used for cutting out complete circles as shown on the right. As can be seen the first few cuts square the circle off. The next few cuts reveal more of the circular shape.

The final cuts should be cut using the flat edge of avery sharp craft knife to avoid tearing the part.