I believe that most if not all bodies of cream separators were made of cast iron.
Well now I can believe that because 95+% of all household and industrial metal implements, etc., were made of cast iron up until the early to mid 20th Century. Cookware, kitchen items, farm machinery, etc., ..... anything that could easily be "molded" was made of "cast iron", which, by the way, is how it got its name of "cast", meaning "to mold".
And those ole timey manufacturers were frugile and t'weren't in the habit of making something 4 or 5 times stronger than it needed to be, and in my opinion the base unit of a "cream separator" didn't need to be as strong as the "per say" one pictured above.
But now iffen you all had told me it was
grist mill mechanism for "grinding" cornmeal, flour, etc., then I probably wouldn't have questioned it .... given the fact that "grinding" corn is a far tougher job than "grinding" milk.
Cheers