Just like a brake rotor lathe the face of the coupling is made to rotate perfectly with the shafting.


If you get a new shaft and the face of the coupling does not look, and had not been freshly cut, you've been cheated of a proper machining job. It would be EXTREMELY rare that a coupling would not need to be faced. They need to install it in the lathe head to check it for run out anyway so the 60 seconds it takes to actually cut the face could be a prime indicator the shop never even checked the facing run out.