bulgie 

It seems to me that the two methods of alignment are equivalent and will give the same results, if the parts (frame and table) are all really "to spec", and stay that way through the alignment process.

For one thing, a BB shell facing tool doesn't really bring the faces to parallel, because all such tools have a little slop and flex in them, which allows the facer to flop over a bit. It will flop away from the side that starts cutting first, so the resulting cut is somewhere between spec and where it was originally. I.e. the facer improves it some but not all the way. The Campy facer is the best I've used (least slop, least flex) and plenty good enough IMHO, but most others I've used had too much slop for the faces to be a good datum for aligning. Even with a Campy you need to remember that your faces are not 100% parallel.

Next is the table flatness and how close the BB holding post is to "normal" (perpendicular in every plane that passes through the BB axis). The table in the Brodie video has a pretty wimpy BB post. The fact that it moved while Brodie aligned a frame is pretty damning. Attaching to the table by only one bolt seems inadequate to me. I know lots of guys have BB posts made this way and get adequate results, but I was spoiled by really mondo posts at the last few places I worked. The table at Ti Cycles is a good example, you can see it on their website. Look at where it bolts to the thick granite table, with four large bolts widely spaced from each other. The central post is joined to the bottom plate (where the bolts are) by a welded pyramid made of four fairly thick plates. The whole thing was faced on its bottom surface in a lathe after welding. (I assume anyway; I wasn't there when it was made. Coulda been done on a milling machine, but a lathe would be logical.) Bottom line is when you align a frame and then flip it, the frame is still aligned!

Another factor that can creep in is the BB faces can squirm a bit on the post, so I tended to loosen and re-tighten the shell on the post after a big heave. I did get different readings before and after retightening, so this is not just theoretical — the shell does squirm where it's clamped. More with Ti frames, but some with steel. Probably the squirm can be minimized with proper post design, but it's something to check for.

I have considered making a BB post that utilizes the Campy threaded inserts that are part of the facing tool. That would give you a good datum for alignment if the post was a precision fit on the ID of the Campy inserts. Downside is needing to fully tap the threads before aligning, which wouldn't work for some workflows, like if you do an alignment check after tacking but before final brazing/welding. Also it'd be very slow, annoying if you're trying to make a living. The opposite of that was the Bike Machinery table at Davidson, that clamped the BB shell faces pneumatically with a foot-pedal, fast and repeatable but $$ and complexity = more things that can go wrong.

Another disadvantage of using the Campy facing inserts for alignment is that the ID is a bit small for my taste as an alignment post. The central "bolt" on the Ti Cycles post is very large diameter, I don't remember the number, but basically as large as it can be and still fit through a BSC threaded shell. I haven't decided yet whether strength is the only thing that matters there, or whether stiffness matters too. Say if you made a small-diameter post out of heat-treated super tool steel that is plenty strong enough, would the springiness of the post adversely affect the alignment? Extra spring in the post would definitely mean you have to move the thing being aligned further to get it to take a set, but that isn't necessarily a deal-breaker, and I'm sure you'd adapt quickly with practice. It could mean you'd need to elevate the frame centerplane higher above the table to avoid bottoming out, especially with Ti. But there's no such thing as too stiff, so the largest possible diameter for the post is probably best.

One reason to use the BB faces as your datum is if you're wholesaling frames to dealers — some of them may have an alignment table, like a New England Cycling Academy (NRCA) or Bringheli. At Davidson we aligned them to the nth degree, not because that's necessary for "riding good", but more as a sales gimmick. If someone checked our frame they'd be impressed, and sell more of them. Of course there's still that whole can o' worms: is their alignment fixture any good? If theirs disagrees with yours, can you convince them that the problem is with their fixture? Very few dealers have such a thing, but we had a few that did, and word gets around.

Again if both methods are highly refined, then there shouldn't be any difference in results regardless of what you choose as your datum.

Mark B in Seattle