Insert the slot stick (masking taped end first) into the mouthpiece through its larger end. The stick should extend out a little through the opposite (narrow) end.
Lay the mouthpiece (with the slot stick still inside) into the cut out in the ocarina bottom.

As shown in the inset, the slot stick should stick out of the mouthpiece approximately 1/2 (one half) of its width. This part of the slot stick will be traced around. Use the needle tool (tool #6).

With the mouthpiece and slot stick held in place, cut through the clay only across the end of the slot stick. (indicated by the arrows) Use tool #7.

Remove the slot stick from the mouthpiece. Hold it along the already cut line. Use the same tool (#7) and slice the sides of the voicing. The slot stick acts as a stop, preventing the the sides of the voicing from being cut beyond its (the voicing) end. (The left cutting line is indicated by an arrow.)

The white "box" in each of the voicing openings helps to define the shape. The voicing opening should look like figure 1 (rectangular). In figure 2, the opening is too square.