You can get BB shells with and with out threads.
http://www.ceeway.com/Aluminum%20Aluminium%20Alloy%20Titanium.htm
Bike Forum
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Bottom Bracket facing
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Posted 2 years ago #
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and what if the shell is faced properly (in relation to the whole frame), but the threads are out? then the BB goes in wonky anyway...
i never bother.
Posted 2 years ago # -
Orange told me not to get the bb shell faced on my P7
What reason did they give?
Posted 2 years ago # -
Thread chasing and shell facing are two different things!
It used to be that the threads were chased on rusty old steel frames to help a new bottom bracket in. That's all.
Facing the shell wouldn't make a blind bit of difference on a cartridge bottom bracket, as the shell of the bb holds it straight. With external bb's that isn't the case.
The reason bb's have to be chased before they're faced is because the chasing tool gives a guide for the facing tool so it's perpendicular to BOTH sides of the bb.
I've chewed off surprising amounts of frame material with a facing tool to make a bare surface.. 1.5mm off a Santa Cruz for instance. The threads were pretty straight, but the outside shell can be well out. As Brant says they're often cut after welding, but this does nothing for the shell face.Posted 2 years ago # -
said it didnt need it
Posted 2 years ago # -
But again, unless the chasing tool ensures that both sides' threads are in line it's pointless except of cleaning up the threads. Most chasing tools are single sided so do nothing to help alignment for external bbs.
1.5mm out on a Santa Cruz? I'd be calling that a manufacturing error! I have yet to see a frame like that though anecdotally know that a few do crop up but they're not the norm. I'd also be interested to know if you were 100% certain that the threads were perfectly aligned in that case too.
Posted 2 years ago # -
Mechanically the best thing is to have 100% in line threads and a 100% perependicular face on each end.
And a bearing casing that locates on the outer face will obviously work best on a faced surface.
As for not facing steel, that is just rubbish. If they said no to titanium I wouldn't be suprised, but steel....! Find another bike shop.
Posted 2 years ago # -
Mechanically the best thing is to have 100% in line threads and a 100% perependicular face on each end.
And a bearing casing that locates on the outer face will obviously work best on a faced surface.
that goes without saying. The discussion is about there's any point facing when you can't be sure the threads are in line.
Posted 2 years ago # -
I'd also be interested to know if you were 100% certain that the threads were perfectly aligned in that case too.
er.. yes, coz I'd just chased them.Posted 2 years ago # -
With a double sided chasing tool? Unusual...
Posted 2 years ago # -
er.. yes, coz I'd just chased them.
if you chase a misaligned thread don't you risk removing it ?
Posted 2 years ago # -
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 here. 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.Posted 2 years ago # -
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!
Posted 2 years ago # -
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)......
Posted 2 years ago # -
With a double sided chasing tool? Unusual...
er... yes. not unusual. All chasing tools screw in from both sides at once, making the remaining thread the best average of either side.Posted 2 years ago # -
Wasn't aware of that, a quick google shopping search 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?
Posted 2 years ago # -
All chasing tools screw in from both sides at once
mine doesn't
Posted 2 years ago # -
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.
Posted 2 years ago # -
if you chase a misaligned thread don't you risk removing it ?
And yes also. I had a "friday afternoon" warranty replacement klein frame that was well out. I removed a LOT of material when I chased it from the drive side. It never stopped creaking until I padded the threads with PTFE tapePosted 2 years ago # -
Editing makes a double post!
As Four Tet say... "There is no such thing as a metal Frisbee."
Posted 2 years ago # -
So you end up with loose threads which you then use as the guide for the facing tool... (single sided of course)
No. The tool faces the shell between guides emplaced in the threads on BOTH sides.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?
Posted 2 years ago # -
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 otherPosted 2 years ago # -
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?
Posted 2 years ago # -
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'
Posted 2 years ago # -
Course it's not. You're relying on the face for alignment, which brings us back to the original point...
Posted 2 years ago # -
I agree with BikeWhisperer, aren't the threaded inserts used for location rather than alignment?
Posted 2 years ago # -
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
Posted 2 years ago # -
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)?
Posted 2 years ago # -
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.Posted 2 years ago # -
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.Posted 2 years ago # -
Here you go, Cyclo usage instructions.
http://www.youtube.com/watch?v=fvgWC3QAGbA
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?
Posted 2 years ago # -
here it is:
Posted 2 years ago # -
Eek! Old to the power of skool!
I was talking about one of these:
Posted 2 years ago # -
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
Posted 2 years ago # -
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 offthe 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
Posted 2 years ago #
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