Originally Posted by
Kuromori
However, there’s another solution to facing bottom bracket shells, using a cartridge square taper BB. The bearings come aligned in the cartridge, the unflanged cup doesn’t even touch the faces, and the flanged cup just bottoms out and is held in alignment by the other cup. Facing BBs for cartridge BBs can be detrimental even because raw steel is exposed to the elements. They also require less frequent service, preserving your crank tapers, and replacement is easier than rebuilding.
Yep, a cartridge BB sidesteps the need for facing. Facing was done during the loose cup era because it ensured that the two BB cups were perfectly aligned with the spindle bearing. If a self contained cartridge is used, facing isn't really necessary. Even so, I'd be inclined to remove excess paint with a utility knife, to get a good seat for the drive side BB flange. Not strictly necessary though. If a traditional BB is used, facing is standard practice and a good idea for top end bikes. It wasn't usually done on mid or low level bikes, because they wouldn't be ridden enough to matter.
If it's a flange-less cartridge Phil Wood, no need for that. Leave the paint.