If the paint is centered and the ball still curves, you need a teacher.
The mill will name a motion problem. It will not fix one. That boundary keeps the arc honest.
A 4-iron that toes in because the player stands up will still toe in after a perfect bend. We will say that in the ledger and point at someone who teaches on the other side of the canal.
If the paint is all toe and the player’s story is 'it used to be fine,' that is mill work.