It is the same procedure that is used for standard gears.
You need to layout the gear as a 1 dp gear and use the same method. You start out by drawing a line from the tip tangent to the base circle. Where this line intersects the centerline of the tooth, draw a line from this point
tangent to the fillet radius. Draw a perpendicular line
from that point of intersection to the tooth centerline. From that fillet radius tangent point draw a horizontal line to the the tooth centerline. x is then the vertical distance from the horizontal line down to the other intersection line at the tooth centerline.
Since y = 2/3 x, you have the lewis factor from the model. I do it in acad often.
