Fully groves mains

Leaving a mark or a scratch is not the same as producing filings and removing metal.
I am not surprised that you do not know that cam lobes are hardened. Or that you are unaware that the toughness-hardness of the material being cut determines the metal shaping process. There are several turning, milling and burnishing methods that could be used to get a smooth cam lobe shape on soft metal, but cam lobes are ground because they are hardened.

I see no reason to continue to banter with you. One does not need know how things are made to be an automotive enthusiast, but it does limit your ability to participate in a discussion.