. Any mechanical gin would be so expensive in metal and skilled artisanry as to only be a one-off toy for the ultrarich and social circle of its inventors, much like Hiero of Alexandria and his steam Aeolipile.
The Romans were building things like harbors, stadiums, and aqueducts out of unreinforced concrete (The Pantheon, for example, has the largest unreinforced concrete dome ever built, and it's almost 2,000 years old). The main reason they didn't build steam engines like the simple early ones used to pump water out of mines: slaves were cheaper.Any mechanical gin would be so expensive in metal and skilled artisanry as to only be a one-off toy for the ultrarich and social circle of its inventors, much like Hiero of Alexandria and his steam Aeolipile.
The Romans were building things like harbors, stadiums, and aqueducts out of unreinforced concrete (The Pantheon, for example, has the largest unreinforced concrete dome ever built, and it's almost 2,000 years old). The main reason they didn't build steam engines like the simple early ones used to pump water out of mines: slaves were cheaper.
As to the original point, a Roman cotton gin: the picture above doesn't adequately show the fine metal parts- interlinked teeth and metal wire- that made it workable for mass-processing of short-staple cotton.
Plus, as @bookwyrm says above, there wasn't any cotton in Rome to gin. The stuff grew in India and the cloth was imported.