How Mexican Cobs Were Made

I was under the impression that cob planchets were made by cutting slices off the end of a thick bar, like salami. Then I ran across this article by Sedwick

http://www.sedwickcoins.com/articles/strap.htm

A weighed amount of silver (8 cobs worth in this photo) was melted and poured out in a strap-shaped puddle on a table. After cooling it was balanced and cut in half, then repeated until there were 8 planchets. Striking was on the top and bottom, not on the end as I had thought. Very simple, and from what I've seen accurate to within about 5% weight based on 8 reales cobs.

There were probably other methods used at the various mints. Many of the cobs are close to round in shape and the strap cutting method wouldn't easily make round shapes.