They know I'm a sadist, run these rappers grills on a lathe

from Jonwayne – Numbers On The Hoard Lyrics on Rap Genius

Meaning

A lathe is the table metal pieces (say, a grill) are placed on when they’re being cut or shaped.
Innoccous by itself, but considering that it sounds like he’ll be reshaping your grill while it’s still in your mouth…

…yeah, ouch.

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