constructing and mounting a porpax

[Giannis K. Hoplite]

Perhaps it helps. But the only sharp rims I have seen are those two that are displayed together in a fighting scene,that I posted above. The rest are not that sharp and have decoration that would help grabing.
The most obvious function of the bronze rim is to keep the planks of wood together. And perhaps as Paul said withstand severe blows on the shield that may have deformed an unrimed shield. Secondarily,it is always better to protect smth wooden touch the ground.
Khairete
Giannis