stock forged cranks, undercut fillets?

guys
they are not "undercut"
they are rolled under extremely high pressure, compressing the metal
really undercut with a tool or grinder would really weaken
rolled are tough and the deformation goes deeper than the depression
what matters is still there
aftermarket grinders do not have the big tooling to roll fillets IMHO rolled fillets are better than ground
It takes a big radius
Here's one of a modified 360 to go in a 318, rod journal under cut still visible, but the mains now have a radius, under cut is gone.View attachment 1715306055

Wyrmrider's got the terminology right! That's how it is.

The only who said "under cut"