I'm talking about this tool here:



Note that it will cut a chamfer into the bb - why exactly do we need this tool? Or is the description wrong? I only ask because the park facer is just a flat mill.

That doesn't look like the original Campagnolo mill...

Perhaps it's the mill that chamfers the shell for a Mavic bb?

As a long-time machinist (started in '71), I can tell you that it is normal for all threads, external or internal to start with a 45 degree chamfer that is 1-2 thread pitches in depth. A straight surface leaves a weak partial thread that is of no value and makes it hard to get the mated parted started in straight.

Most parts with internal threads define the thread chamfer to be slightly larger than the major diameter of the thread.

I should add that the tool shown doesn't look like it would do both face and chamfer an ID, but I'd need to see the end of the cutter more closely.

Also, most facing jobs should only require a small fraction of one thread to be removed.

What DaveSSS said makes sense, but that tool does look very much like Mavic's BB chamfering tool.
the 80's/90's Mavic sealed cartridge BBs do not use the bike's BB threading to anchor itself to the frame. It does it with just pressure from 45 degree faced lockrings on both ends of the BB that will seat on to the chamfered faced BB provided by the Mavic tool. A nice idea that would have eliminated all need for trying to figure out what threading your BB is when it comes time to change your BB, but I suspect Mavic wasn't too generous with sharing the patent and technology for this with other companies and it "Betamaxed" itself out of existence, plus other better(?) BB designs came to be afterwards ......although,.......don't Phil Wood BBs kinda work the same way??

Chombi
84 Peugeot PSV
85(?) Vitus Plus Carbone 7

Phils use conventional threads.

I agree with Helomatic I do not think that is the "facing" tool. also what Dave and Chombi said are correct too if you are dealing with a Mavic cart BB (I think VO just came out with one)

now to answer your question about the too. the 'facing' cutter should not chamfer the BB shell but it is designed to remove paint and "square" the sides of the BB to ensure they are parrallel. this aids in getting the fixed cup tightly into place as well and making the lockring lock tighter. 'facing' and 'chasing' was standard practice on all frame (build up in shops anyway) and I normally did it ( atleast facing) on overhauls. there is also a tool for 'facing' the headtube as well.

Just a slight correction. Facing makes the face of the BB shell perpendicular to the threads and insures that the face is truly flat, if the cutting is done carefully. I've never had it done to a frame in 25 years and over a dozen frames.

The cutting bit comes off, right? Maybe it's missing a flat one.

I agree. That looks more like the Mavic cutter than the Campy. The one on my tool kit is not chamfered:



Look for markings on the cutter; if it's actually a Campagnolo cutter, it should say so:

I'll be glad to get that useless Mavic BB tool out of your hands Pronto!

Chombi

Just a further off topic interjection, the VO BB fulfils the same niche as the Mavic (reviving frames with buggered up, or obsolete BBs) but does so in a way that doesn't involve cutting on the bike of any sort.

Do you want a Mavic BB mill? We have a couple at work. I've never seen them used once. Tell me how much you want to pay and I'll see if they want to sell one.

lol

I have.

For example, modern bb's like phils and sugino 75's are very intolerant of shell face misalignment. I've seen a fresh steel frame so bad that a standard shimano square taper cart sat noticeably off because of facing issues with a bb.

At any rate, I have that exact same cutter on that tool, that would be quite a coincidence if it is in fact the mavic tool.

How can a Phil BB be "very intolerant of shell face misalignment" when no part of it contacts the shell face?

What I do to check for the need to face a BB shell is install the cup and thread it in until it touches a .010 inch feeler gage. Then I use feelers in the .008-.012 inch range to search for high or low areas. If any area exceeds those limits, I'd face the shell. Always remove any paint from the face of the shell, first.

Anyone installing a Campy UT crank should do this and then measure the BB shell width, which must be 67.2-68.8mm to work properly. A lot of failures result from failure to do one or both of these procedures.

I hope you don't do it for every overhaul of frame that has been faced properly once. Once a frame is properly faced, it should never need it again unless it is repainted and then only to clean up any overspray.

All repeated facing accomplishes is to narrow the bottom bracket shell until the bottom bracket doesn't fit properly. Do it once (only if needed) and leave it alone after that.

My experience mirrors DaveSSS's. I've built up three Litespeeds Ti frames and a Co-motion steel frame from scratch as well as bottom bracket replacements on several other bikes and none of them has needed facing.

I converted a 2001 Gary Fisher Hoo Koo E Koo to Shimano outboard bearing BB/crankset. I brought it to a very reputable bike shop to have it faced and they turned me away, saying it wasn't needed. I removed the paint with a single-edged razor blade and installed. No binding, premature bearing wear, works great. Similarly, I built up a 2001 Ti Spectrum this year with Chris King BB and simply removed the Imron paint with one of my wife's emery boards prior to install (I know that Merlin does a good job of facing BB shells, so I wasn't too worried) and all is well with that bike too. I like the feeler guage method of checking the facing, I'll definitely do that in the future.

K thx.

Well, the tool you pictured looks like an amalgam of Campy and Mavic parts. Here's a page showing the Mavic cutter:



The text describes it as "adaptable to Italian tool holders" by which it likely means "Campagnolo."

You can see that it bears little resemblance to the Campagnolo #725 bottom bracket facing mill:



But it does strongly resemble the cutter in your original picture.

He might be referring to Phil Wood external bottom brackets.

Regardless of the situation - facing the bottom-bracket is becoming essential with any frame - due to the external- BB's becoming more and more popular. But a notice should be with the bicycle to identify this task having been accomplished.

I can just see Joe bringing his bike for help - and the BB-shell is 58mm......

A competent mechanic can find said notice on the bottom bracket shell itself. If they can't tell the difference between a properly faced bottom bracket shell, and one that needs facing, they shouldn't be anywhere near that tool.

HillRider wether I faced the BB on an overhaul depended on the bike of course. if it was one of our bikes and the faces were relativly clean I ight not. if it was an older mid to higher end bike and I was installing a new BB I certainly would.

and yes facing is a very delicate operatin like turning brake rotors. actually in most cases very little if any frame material is removed.

Facing a steel frame creates a great place for rust to get started and it can run right up under the paint on the BB shell.