As a result, the sill -- or its outside end called the "nose" -- often rots or cracks before any other part of the window frame begins to deteriorate ... Cut a 5 by 15 or 20 cm (2 by 6 or 8 inch) ...

so that the depth of the saw blade is the same as the thickness of the sill. Begin the cut at the outside edge and proceed towards the window. Take the cut as far as space will allow then turn the saw ...