... I once solved this problem by using two identical hammers and
putting one in a vise to use as the "anvil". Very tedious trying to
keep the hammers centered. I think making a device incorporating
two domed surfaces and a long u shaped connecting piece to keep
them aligned might solve your problem.
Now that sounds like a very promising idea! Thank you for sharing
I understand that bladesmiths use a similar tool to create the fuller
(lengthwise groove) on sword blades and the blood gutters on large
hunting knives. There is a picture of such a device in Jim Hrisoulas'
book "The Master Bladesmith", p. 170.
I can imagine that one could make a simple version with a length of
strap iron and a couple ball bearings. Hmmm, must put that on my "try
in The City of Light