how would i do this?

[pugs]

How hard is it? You say hard but no Rc number. If it is only Rc55 or lower, just face it off in lathe with carbide tooling. Light cuts bit high on the SFM.

You'd be amazed what coated carbide can do. H&ll I machined a pocket in a file on my VMC with a 1/8" endmill just to see if a could. Endmill was shot when I was done but it did work.

If no accuarcy requirement, an abrasive cutoff wheel of some sort (air powered or dremel etc). will do it as well