So is the tapping/chasing tool machined in such a way as to do something more specialized than, say, screwing the bottom bracket in carefully, then removing carefully, and then cleaning the threads up with a rag? From the pics I see, the tool doesn't look like much more than another set of threads. Also, when I use the term "tapping" and you use the term "chasing" are we talking about the exact same thing?Yup, just cleans the threads and makes sure it's round. Depending on manufactures methods or order of op, the BB could be threaded before the frame is welded. During the welding the heat, expansion and then the contraction after with restriction do to the new structure attached can mildly distort the bb tube. Chasing makes sure it goes back to round by re-cutting the thread in the tight spots. It also for older frames that had a stuck internal bb that was removed with a little extra persuasion
If threads are bad screwing in a bb won't help no matter how many times you do it. A bottom bracket chasing tool is designed to cut metal and has grooves to clear the material it removes. Tapping and chasing are two different things. Tapping is cutting threads where none existed, chasing is cleaning out ones that are already cut.
Both procedures are accomplished with a Tap and that can lead to confusion. A Tap is a threaded tool constructed of hardened steel with flutes cut lengthwise. The flutes allow excess material to be removed (like the flutes on a drill bit) and they create cutting surface for the threaded portion of the tap. Essentially, each flute creates a sharpened edge for each thread. Taps come in two basic configurations standard (with tapered threads to allow the gradual increase of thread depth) and bottoming (without tapered threads, to ensure a blind hole is tapped as deeply as possible). Park Tools sells a facing and tapping set, the tapping tool will chase threads as described by J.B. above. One reason so many folks face and chase their BBs is that in production, these tools can wear down or be slightly off center when used. If your BB-30 (or other BB system) is not installed on a trued and flat face it will tend to creak. Lots of things cause the threads to become problematic (including worn taps during manufacturing). I've had every bike I've build from frameset faced and chased. Always seemed like a good dose of prevention and relatively inexpensive. I pay the LBS here so I'm not investing in a one or two use tool (they're pricey).
This should be C&P'd as a reply to every post where someone thinks facing and chasing the BB shell has anything to do with paint.
ya, it depends though as some of the manufactures not tap the BB after the welding.. (I believe Giant does this now but not 100% sure)This should be C&P'd as a reply to every post where someone thinks facing and chasing the BB shell has anything to do with paint.
