Use the slot stick to support the underside of the voicing opening.

Mark sides and crosswise as shown. These marks define the area where the bevel or "ramp" will be cut. The ramp outline should be about the same size (indicated by the black arrows) as the voicing opening (white arrows)

With the slot stick still supporting the clay from beneath, use tool #7 to shave away clay on the top (indicated by purple in Figure 5). While cutting, the tool should be angled downward toward where the slot stick meets the clay (Figure 6).

The point of the tool should touch the slot stick where the slot stick and clay meet.

The voicing opening. It should look something like this.