I draw my volute carvings by following a simple sequence of lines and focusing on a few requirements. I begin by drawing a line near the outer perimeter as seen in drawing A. Then I draw a larger radius curve out to the flat area as seen in B. It doesn't matter if it is perfect, it is a reference and can be changed later.
Drawing C shows the beginning of the interior shape. When drawing it, my goal is to have the negative space above the line by decreasing. Another way to put it is to say that the line will be moving closer to the line from drawing A. A small point worth mentioning is that the initial boundary of my volute is a true circle, but the final shape diverges because as the volute wraps around, it's radius decreases. This can be seen in the small space on the bottom right of the carving. I carve this area away later.
Drawing D shows the final wrapping of the line to form the inner circle.
My main focus for a successful drawing is the negative space (shown darkened in drawing E). This shape should be a curved taper. If any part gets thicker as it head towards the center termination, I know that I must adjust something. My goal is to have the eye follow without interruption to the center of the carving.
Below is a photo of the incised line that I make as the stop cuts for my carving. By using gouges of differing sweeps in sequence, I can follow and refine my drawing. I don't make the initial cuts too deep in the oak, a couple of passes is better and helps me to define the depth of the carving.
Designing your carvings can be done around the tools you have available. Play around drawing the shape and then see where your tools might fit, I always prefer a compromise between the tools and the drawing versus buying every useful gouge!