customizing round bosses for dished shields

[Orlirva]

I checked here a few months ago for advice on modifying a 'standard' round commercial (spun) boss/umbo into one that would fit a curved surface… in my case it was a 6th c, deeply curved (not concave) oval shield, and also byzantine concave-dished shields. I did not find any information ( except that it was hard to do), and a reference to a german firm that would make one custom – I would gladly have gone that route and aquired a nicely made forged (not spun) boss, but they had a steep minimum order requirement to ship to the USA and so it fell outside my budget.

I tried it and did not find it hard although it took a couple of hours of fussing. When I knew how to do it I was able to do another one for a concave shield in about an hour. The main tools required are a sturdy vice and a large ball peen hammer. I found two ways to get 'dish' and a combination seems to work best:
1) lay the boss upside down on vice's top (or other anvil-like surface), hold it with a gloved hand, and beat all around the inside bend with the peen; work the two sides that you want to curve down extra hard.
2) I was also able to wedge the boss into the vice and use the vice power to squeeze out the inside bend… although if you do that too much it will get a big dimple, so its best to give it a light squeeze, move it a centimeter, and squeeze again, working around and back again if necessary.
3) A third technique is needed to finish the job: using the vice to get the down-bend/curve in the flange just right. Basically the jaws are not tight, but just provide a place to wedge the flange and you use muscle power and leverage to bend the flange. Again it took multiple light bends working around, rather than one big bend… and start deep and inside and do the outside edge last. The bends are for fine tuning and don't provide the 'dish', or not much anyway … If there is not enough dish you need another round with the hammer (1) or the vice squeeze trick (2).

Using some scrap leather on the vice helps not mar the surface, although I ended up scouring and polishing the whole surface afterwards, and that was ok too.. THe inside edge looks dimpled, but in my case the dimples are fairly small and even and so not at all bad and the boss certainly looks a lost less like a modern spun product.
Rick