Originally Posted by
restlessswind
I highly suggest removing the bottom bracket before drilling, then clear the fragments out before reassembly.
Why? If any happened to get in they'll just sit on the bottom of the shell most of the time. The steel of the shell is also probably softer than the bearings so even if they made it through all the grease that been pushed out of the bearings and into them, they'll just be ground up and mixed in. Metal particles are actually used in greases to improve some qualities.
And if this is a cartridge BB then none of the swarf from the drilling can even get in. Though without looking at the pic again, I think that looked like cup and cone. Still wouldn't bother me though. The swarf comes up from the hole being drilled and if used with a vacuum cleaner while drilling and they don't let the drill plunge when they break through the shell, then little to no chips will get in.