The three circular templates (actually two cups and a plate) are used to make concentric rings at the corners of the head, another pair of concentric rings at the centre, then two more offset to either side. The plat is then used to blend these rings into each other at specific points. This is more instinct and art rather than science. Then I mark where elements of the design weave over and under each other. Identical designs are drawn up on the front and back.
With this laid out, it's time to start carving. A good sharp hobby knife is fine for cutting through the foam of the yoga block being used. The blade is held diagonally as I cut into the foam, with the tip of the knife digging into the centre of the marker line, while the blade plunges through it's edge. Two cuts will be used for each line on the foam, one on each side of the line, meeting up a few millimetres below the surface due to the diagonal cuts.
As I get close to finishing these cuts, the hammer head looks like this. Both sides are cut in this manner.