[Closed] Bottom Bracket facing

If a frame needs facing it needs facing, no matter whether it's made of aluminium or steel.

Yes, but I just found it strange they wouldn't do the steel frame as they're quite a high class bike shop (i.e. expensive!).

Facing is a myth. It does nothing to ensure that the two sides are parallel to eachother, only that the thread and face on each side are in line.

Save your money.

If you use a proper bb facing tool then it ensures both faces of the bb are parallel to one another.
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And how many shops use one of those? Most are single side tools.

If you use a proper bb facing tool then it ensures both faces of the bb are parallel to one another.

so does that mean if the threads aren't already parallel, they get mashed up by the taps - or are they floating ?

They way the threads are cut initially the threads will be in line with the tube, so unless the bottom bracket shell is actually kinked (virtually impossible it will do what it is supposed to. What it does fix is ends of the tube which makes the bb shell which may not have been cut perfectly square.

They way the threads are cut initially the threads will be in line with the tube, so unless the bottom bracket shell is actually kinked (virtually impossible it will do what it is supposed to.

which sounds like you're contradicting yourself, inasmuch as, if the threads are necessarily parallel then a one sided tool would work fine

I've had that "it blunts the tool" BS myself. I took my business elsewhere and never darkened their doors again. Just a shop too lazy to do one little job in my opinion.

I'd go to the other place and have it done.

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And more to the point Simon, if you trust the threads to be in line on both sides then why not trust the faces to be also? Cutting threads perfectly straight is harder than producing a flat face on something that is typically
turned from tubing (at least that's how I understand they're made)

if you trust the threads to be in line on both sides then why not trust the faces to be also?

well, yeah - but then I always thought facing was nonsense 🙂

Cutting threads perfectly straight is harder than producing a flat face on something that is typically
turned from tubing (at least that's how I understand they're made)

I thought the BB shell was machined to tolerance, then welded into the frame on the jig, then the threads cut relative to the jig alignment.... so, the threads [i]should[/i] be 'perfectly' aligned with the other key points on the jig, but the shell itself may have distorted during assembly so the end face may no longer be flat/parallel. Therefore, single sided facing is still valid as the threads [i]should[/i] be a good datum. Happy to be corrected by the frame builders lurking on here 😉

facing = bike shop con #427

I'd be very suprised if threads were cut relative to the jig rather than the bb itself (and that's assuming that they're not cut before weling to the rest of the frame) but i'd be interested to hear for sure.

Yep-complete con, I mean why would any bike shop pay £hundreds for a specialist tool, to charge £10 a go to face frames when there's no point aother than ripping people off?

I thought the BB shell was machined to tolerance, then welded into the frame on the jig, then the threads cut relative to the jig alignment.... so, the threads should be 'perfectly' aligned with the other key points on the jig, but the shell itself may have distorted during assembly so the end face may no longer be flat/parallel. Therefore, single sided facing is still valid as the threads should be a good datum.

They're not.

why would any bike shop pay £hundreds for a specialist tool, to charge £10 a go to face frames when there's no point other than ripping people off?

To make profit?

something that you may be disregarding, is that the process of welding can distort the material. So what was within a certain tolerance when it left the tube shop, may end up outside those tolerances once welded into a frame.
No idea how it affects external BB life, but I suspect not by much, if at all.

This facing lark does seem a little odd..
a rigid bearing cup which surely can't get affected by a tiny bit of paint build up..
provided the cup is fitted to the correct torque.. the thread is cut into the frame straight the imperfections on the face should have little influence on bearing performance or life..

Has anyone ever put two straight edges across a BB shell and measured the run out ?
If the maximum error is x mm and the plastic spacer washers compress by y mm when the bearings are tightened, then as long as x<y, what's the problem.

Brant, since you're on, what is the process? Weld bb then cut threads or cut threads then weld?

Facing, while in theory makes sense seems to have too many contradictions when you look into it in
more detail in the real world.

Right - thanks Brant 😉 So, as Clubber suggests, the threads are cut into the BB blank shell and welded into the frame as it? Are the threads chased again after welded to account for any welding distortion, or is the distortion judged to be minimal on such a (relatively) thick walled part?

Edit: Damn your faster fingers Dylan!

My point is, there isn't much to be made from facing BB's, with the cost of the tool, new cutters every so often, workshop running costs etc. It takes a hell of a long time for the tool to even pay for itself.

Shops have to buy the tool because customers want the service because they've been told they need it (so some distributors can spuriously avoid bb failure warranty claims IMO). Doesn't make it right.

Bristolbiker - I guess I know you? Who?

Higgo +1

Bottom Brackets should be exempt from warranty claims. They are subject to so many variables which affect lifespan.

Uni MTB club days.... oh, and you bought some single sided road spds off me few years ago now 😉

Er... Can't recall buying pedals 😯

Bottom Brackets should be exempt from warranty claims

Eh? They should do the job they're supposed to. If they don't (particularly when they die in a month even when installed in line with the instructions onwhich incidentally, Shimano don't mention facing) then replacement is right and reasonable.

Maybe we should face the plastic spacers and back of the cups too? 🙄 🙂

I seem to remember that lots of alloy frames are made with unthreaded BB's. Which are then tapped after welding, and after heat treatment.
Frames are clamped by head tube, seat tube and maybe the dropouts, and the BB tapped in line by a big machine.

I'll try and get some more pics when I'm out again in a couple of weeks.

Orange told me not to get the bb shell faced on my P7

Surely the plastic spacers will deform more than the BB shell or the cups and probably even out small discrepancies?

You can get BB shells with and with out threads.
http://www.ceeway.com/Aluminum%20Aluminium%20Alloy%20Titanium.htm

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.

Orange told me not to get the bb shell faced on my P7

What reason did they give?

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.

said it didnt need it

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.

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.

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.

I'd also be interested to know if you were 100% certain that the threads were perfectly aligned in that case too.

With a double sided chasing tool? Unusual...