Do You Chase and Face.....
Your bottom bracket shell?
I was having some bottom bracket issues in the last few months (3 toasted in 200 miles), and decided it was time to get clinical on that b!tch.
Went and picked up my CK bottom bracket, and the LBS let me take home the Park tool required to perform this operation. It went pretty smooth, but ohhh man, I now know why my bearings were not liking me. To get the faces of the shell milled parallel to eachother resulted in more than a few metal chips laying on the floor. I would be interested to know what process they used to cut the bottom bracket shell, as whatever it was I would not use to mass produce bikes.
Got everything bolted on and snugged up and went for a ride, and so far so good. Hopefully that will be the end of my bottom bracket issues for a while.
Most higher end bikes have their shells, at the very least, faced before they leave the factory, but well before they are painted. Uneven paint, then, can cause non-parallel faces, which can cause issues, as you've found out.
That said, I have my bottom bracket shells chased/faced the first time I change my bottom bracket, so at least I know that everything is hunkey dorey. It's worth the $30 or so up front to rule out the problem down the road.
Quality of thread cutting and general alignment issues are less than they used to be, especially with carbon frames not having the cooling welds/misalignment bit. There usually will be a couple of bad ones that sneak through. I can't say I've felt the need of late, however more and more of my bikes have been press-in's
Rimmer - "There's an old human saying - if you talk garbage, expect pain"
If it's a threaded bb shell and I intend to install an external bearing bb, yes always. As noted many manufacturers do face the bottom bracket shell on their mid level to high end bikes. However most do it before painting. Kinda stupid because uneven paint or finish on the faced surface can defeat the purpose of facing. Even on frames that I know were factory faced I chase the threads anyway so it's not a big deal to put the facing cutter on a give it a couple of turns just to check it. I've found a few that were factory faced that weren't quite right, so it's worth it to check.
"I do whatever my Rice Cripsies tell me to!"
I've built 5 bikes up this year. 4 of them got external BB's and they were faced and chased.
It hurts on a cheap frame paying almost as much for BB and headset prep as you paid for the frame but I didn't want surprises later.