[Retired_for_now]

Thanks all,
Swampfox, Jeff has it right. I cut out the tire sidewall disks freehand or with a circle cutter if appropriate. The drill gauge simply supplies a form for the coiled up strip of card. The coil expands to fill the hole and makes a perfectly round tread section. By using several layers of card you get a good surface to glue the sidewall to (no little tabs around the tread or edge gluing) and you get a round tire that's easier to make than the alternative of laminating several thick card disks (more circles to cut). The strip of card is just a long, thin rectangle that's rolled up to fit in the hole.
I'll post more pictures shortly - including the all-purpose, portable hole (sometimes the best tools are the simplest).
Yogi