[Closed] Bottom Bracket facing

er.. yes, coz I'd just chased them.

if you chase a misaligned thread don't you risk removing it ?

Clubber,
When designing any mechanical system you should do so ensuring it mates to an aligned face, you should never trust threads to align an object. This has been discussed in the past [url= http://www.singletrackworld.com/forum/topic/tapping-and-facing-bb-shell-really-necessary ]here[/url]. The threads should be aligned to the longitudinal axis of the BB shell, unless the faces are drastically out then there should be enough play in the threads to stop anything seizing before mating to the face itself. Makes good engineering sense imo.

I know that, thanks.

Once again, my point is that most facing tools are single sided so do nothing to ensure alignment between the left and right side cups which is the whole point!

Mechanically the best thing is to have 100% in line threads and a 100% perependicular face on each end.

I don't think that, in a ideal world, achieving this goal is in question..... the argument is a) whether it's worth going further than the as-manufactured toleraces and having the shell faced and b)whether it can be achieved in a workshop environment (RE: single sided facing tools)

Brant's description for 'mass produced' aluminium after welding/heat treatment and the link to pre-threaded shells has muddied the water for me - makes me think it comes down to knowing how the frame was built as the whether it's worth it or a waste of time/money. I know I've had to have it done in the past on a very cheap road frame as you could see that, when 'fully tightened' the BB was touching the face of BB shell in one position, but there was daylight between the two parts 180 deg around (if that makes sense)......

With a double sided chasing tool? Unusual...

Wasn't aware of that, a quick google shopping [url= http://www.google.co.uk/products?rlz=1C1GGLS_enGB353GB353&sourceid=chrome&q=bottom+bracket+facing+tool&um=1&ie=UTF-8&ei=TYiOS4yzLJGUjAfktMCGDw&sa=X&oi=product_result_group&ct=title&resnum=1&ved=0CBMQrQQwAA ]search[/url] doesn't seem to agree with that, at least all of the tools are taking the opposite face as a reference point. Therefore facing each side in turn will see incremental improvements in the alignment of the faces? I've never seen a facing tool which doesn't reference the opposite side. As has been pointed out, is that not a thread chaser?

All chasing tools screw in from both sides at once

mine doesn't

So you end up with loose threads which you then use as the guide for the facing tool... (single sided of course)

edit - and what sfb said.

if you chase a misaligned thread don't you risk removing it ?

Editing makes a double post!

As Four Tet say... "There is no such thing as a metal Frisbee."

So you end up with loose threads which you then use as the guide for the facing tool... (single sided of course)

FYI there is no such thing as a single sided facing tool.

edit..

All chasing tools screw in from both sides at once

mine doesn't

Show me it.. I've never used one like that, and surely, WTF? What numpty would design one like it?

Show me it.. I've never used one like that, and surely, WTF? What numpty would design one like it?

I can't post a pic till about 11.30pm...
basically it's a 2 taps, a left and a right hand threaded, joined by a narrower bar, so you can screw in one end or the other

basically it's a 2 taps, a left and a right hand threaded, joined by a narrower bar, so you can screw in one end or the other

So you screw both sides in at the same time, giving you the best average of both threads. How were you using it?

FYI there is no such thing as a single sided facing tool.

IIRC the Cyclus one in Wiredchop's link is single sided in the sense that the thread the adapter into one side (and only that side) and you face on the otherside of the BB shell.

So you screw both sides in at the same time, giving you the best average of both threads

This is the rub - you are still relying on the the threads being aligned. As you say yourself, if they are not then the alignment bar through the two threaded adapters gives you the 'average' alignment on both faces relative to the two threads.... so neither the two threads nor the two faces of the BB shell are actually aligned with each other. I'll admit it's better than nowt, but I'd hardly call that 'perfect alignment'

Course it's not. You're relying on the face for alignment, which brings us back to the original point...

I agree with BikeWhisperer, aren't the threaded inserts used for location rather than alignment?

So you screw both sides in at the same time

no, you cannot, in order for both taps to engage you'd have to drive it right through the BB, crossthreading both threads

Course it's not. You're relying on the face for alignment

But you just said that the threads make the alignment?? I.e. - if the two threads are parallel, but the axis through them is offset from one another by 2mm, the guide bar through them will be at some angle relative to either thread (they must be - that's just trig.), and if the tool uses the guide bar as the datum to cut the new face it will not be perpendicular to either thread. Is that not how it works (genuinely looking for a walk-through as to how you would do it to better understand this)?

Sorry, spoke half a sentence there!
The chasing tool uses the threads for allignment, to get the best average between the two.
The facing tool then uses both the threads for a guide as it cuts the face.
The BB then uses the face for allignment and hopefully after all the chewing, that's square.

Park Tool say in their instructions for the Bottom Bracket Facing Set BFS-1:

NOTE: The accuracy of the facing can only be as good as the accuracy of the threading in the
bottom bracket shell.

Here you go, Cyclo usage instructions.

I've had it done and consider it money well spent. It looks like it would align better than a non-machined painted surface. I think it should be done in the factory. Perhaps Orange do this?

here it is:[url= http://9x1fqg.bay.livefilestore.com/y1p5AmgHk68QKF5Z1ql8JD4WQQcGW_Li1oXmjSI2SQZcFSCSC5EfO1QyOa3pI4dHKeAPk15w4lsjT19QQI6r6YgGabZ7VvRZgqR/DSC_0364b.jp g" target="_blank">http://9x1fqg.bay.livefilestore.com/y1p5AmgHk68QKF5Z1ql8JD4WQQcGW_Li1oXmjSI2SQZcFSCSC5EfO1QyOa3pI4dHKeAPk15w4lsjT19QQI6r6YgGabZ7VvRZgqR/DSC_0364b.jp g"/> [/img][/url]

Eek! Old to the power of skool!

I was talking about one of these:
[img] [/img]

the CYCLUS tool pictured at the start of the thread is a great bit of kit.

First you cut/chase the BB threads.

Then you can face the BB faces one after the other, or at the same time (would take two people).

If you look at the picture, there are four cutting pieces to the tool. Two independant thread taps and two independant face cutters.

The tool Simonfbarnes pictured is very old, and is not something i would EVER use in a frame. I have witnessed a poor quality BB tap rip all the thread out of an aluminium bb shell. I would only use a high quality tool, which aligns the taps as you thread them in. Just like th eCYCLUS tool

erm here goes this is a big cano of worms when it comes to welding a frame up and i think people are getting parralel and concentric mixed up

bb shells are mainly blanks and when they are put on a jig theres often extra material in the wall but they do have a thru bore which could be described as a datum

welding distorts the shell so even if it was turned as a round tube it wont be after its welded in Most cases a machine is used to firstly remove the extra material down to the threads minor dia then the actual thread is put in whilst the frame is mounted in the same position

the ideal way to to make people and bearings happy and get the threads concentric is to thread in one operation from one side of the frame

due but due nature of one thread being lh and one being rh this is harder than it would seem unless you have a stubby tap and releived internal shell so in production world the frame will need turning over...this may mean a loss in concentricity as you need to unclamp the frame and turn it over and reclamp it

there are machines which do both sides in one op but this relies on the concentricity of the two guides as they go in

invariably despite the best efforts frames are not always straight
so when it is replaced opposite side up the faces which whilst parralel may be out of line with the frame and when its clamped back down the axis mof the shell may be off

the bb30 spec calls for the shell to be bored in one hit ensuring concentricity on both bearing bores so theres no loss in concentricity of the bearings cannondale have a cnc machining centre dedicated to keeping the head tube and BB at 90 degrees plus or minus a gnats cock to each other....i have seen it

facing a frame will allow parrelelism of the faces of the shell and hence the design of the tools will mean it should be parrallel to the thread bore but this will only be relative to each side

the two sides could then be considered seperate datums

when an inline tool is used one side will be happy to go down the thread and sface the shell and the other may just take a little bit of material from one side of its bore and maybe a lot from the other this could mean the thread axis is not inline with the shell bore ...in most cases you wouldnt really notice but some are just dogs and you end up with a weedy thread or in the hands of a beginner a shell which was worse than when you started

the worst case is that you will have parralel faces and one bore thread being on axis with the other side again on axis but being unconcentric in the reference to the other thread

it gets complicated after this and is more than you could go into on a forum the correct term i believe would be the axis runout and perpindicularity of the faces to both or in the case of thru bored single axis

what he said.

Sorry, can't re-read the entire thread but both of those last two pictures are of tools to chase the threads of a BB, not to face the end of the BB tube.

The Park Tool is VERY different
[img] [/img]

The left hand section screws into the BB shell to ensure perpendicularity of the facing tool, however just interested as to what people think, as chasing BB threads are completely different to facing a shell.

You need to read the thread to understand why chasing is being discussed 😉

The tool Simonfbarnes pictured is very old, and is not something i would EVER use in a frame

Oi! Don't diss my tool! Of course, in the days when that was in use, all that mattered was being able to get the internal BB to go in, as it sorted all alignment problems itself. I'm still dubious about any advantage to external BBs when a £5.50 UN26 sq. taper requires no expensive facing and runs wihout any form of maintenance for over a year even when subjected to frequent immersions in deep water - something external BBs don't seems to like (or so I'm told)

Most, if not all, BB shells are prethreaded
http://www.ceeway.com/NEWPARTSPAGES/Other%20BB%20shells.htm

To reduce tool wear the cutters can be TiN coated
http://www.yellowjersey.org/tin.html

One thing nobody seems to have mentioned is facing down to a specified width. Obviously Shimano and similar types won't require this as they have an adjustable pre-load, but Race-Face require the shell to be the correct width, even fractionally too wide and you'll be destroying bearings with the frequency they're known for(We haven't had any returns since facing any of these that even felt remotely tight).

Thanks Bikewhisperer - crystal clear what you meant now. It does now mean that when I go into a shop and ask if they can if they can do BB facing I also have to ask what tool they'll be using etc etc to better understand if it's worth it. 🙄

http://www.cyclus-tools.eu/tretlagergehaeuse.html?&L=3

Don't worry bristolbiker.. They won't be using Simon's tool on it! 😉

Yeah, fair point 😉

They won't be using Simon's tool on it!

it's not about [b]size[/b]...

ya ya.. nobody else mentioned size, did they?

nobody else mentioned size, did they?

someone had to

A whole chapter (chapter 3) on BB facing in The Barnett's Manual of Bicycle Repair

http://www.scribd.com/doc/16958306/The-Barnetts-Manual-of-Bicycle-Repair

Plus how Lynskey do it