Couldn't the bottom bracket cup chip the paint and expose the bare steel?

Anyway, I normally face and chase shells if a customer brings in a frame and wants an external BB crank installed. I hardly ever take apart an OE build to face/chase unless its being build for a special customer or has specifically requested it.

One question for all you wrenches, what do you do with carbon bikes with aluminum or ti bottom bracket shell inserts? It seems risky to try to face those shells. I built up a carbon bike recently (I think it was an ADK frame) with a Al BB shell insert. The faces didn't look to be perfect but I played it safe and didn't face it. A ruined BB < ruined frame