I'm not quite sure how to say this, but I think you have a BBQ grill placed in the middle of your table.
The grill grid can be viewed in your last photo. Well it just so happens that Big Boy Manufacturing made a BBQ Brazier with hood and spit motor in the 50's. I've attached a photo to show you an example. I'm guessing that later someone covered it with a circular piece of wood to make it a Lazy-Susan. Perhaps, for a work table...I don't know for sure.
One has to wonder if they prepared hibachi dinner on this table prior to the Lazy-Susan addition - ha!
From your photos, it also appears that the top of the legs are wood and the bottom are metal (like they were combined) Is that correct? And the table top appears to be wood on the surface....but, is it metal underneath? And, is that the part where the National Cash Register Co, Made in Dayton, Ohio is located?
Thank you....