I have an 83 vintage steel internal cable routed frame I'm building up. I'm looking for some direction as to how the derailleur cables are routed through the BB. My bike has a 3mm hole in the chain stay BB area for the FD cable to exit. I'm wondering if anything special is done here. I have in my mind over time the cable rubbing against the edge of the hole will cut into the base metal. How's yours?