timo888 

Thanks for that information. I think it explains what I'm seeing. Would it be possible, after having chased to rectify a distortion where the BB shell had been pulled up and back slightly by the welds, to arrive at something like this (somewhat exaggerated in the drawing) result on the NDS, so that someone might attempt to make it prettier by aggressive facing of the NDS in order to diminish the size of the "crescent" area that was created when the chase realigned the axis?

P.S. The steerer insert you turned is working beautifully! :-)

dsaul

I'm glad I could help with the steerer.

Is the issue with the bottom bracket a gap where the bottom bracket contacts the face of the shell or is the whole crankset off-axis when installed?

If there is a gap, that is to be expected if the shell was not faced after welding. Facing can fix that, if you have enough excess width to allow removal without making the shell too narrow. The shells that I use to build frames start out being .5mm wider than spec.(68.5mm or 73,5mm) and, after welding, the area roughly in line with the seat tube is less than the spec. of 68 or 73mm, When I face the shells, I can get about 90% of it flat without going under 68 or 73mm. That is plenty of surface area for the bottom bracket bearing to register against.

If the crankset is off axis after installation, there is nothing that can be done to easily fix that. I know some of my frames have the bottom bracket less than perfectly aligned with the rest of the frame and it doesn't seem to be an issue in practice.

timo888 

The BB shell was faced at the factory, according to the company that sold me the aluminum frame. There's bare metal on the faces, not paint, and the aluminum is dull gray, oxidized, not bright and shiny.

The width of the BB shell varies between 67.2mm and 67.5mm, depending on where around the face the measurement is taken.

On the NDS the cup's threads are visible, proud of the BB shell face, from about 1 to 4 o'clock but the cup sits flush or even a little countersunk from 6 to 11 o'clock. At 2-ish on the clock face there is about 0.55mm of cup threads standing proud of the BB shell face, and a gap between the cup and the shell there.

The cups thread very smoothly into the shell. I slowly turn the cup in the loosening direction till I hear/feel the CLUNK when the thread catches, and then reverse direction, tightening with light finger pressure. No resistance at all.

The cartridge BB spindle spins freely. I've got a 1.75mm thick spacer on the drive side.

Nessism

Is this the actual problem statement? The NDS cup is not sitting flush against the BB shell face?

timo888 

I don't know what the problem is. I can only report what I'm seeing. The bike is not built yet. The NDS cup is noticeably proud of the BB shell face only in the top right quadrant. In the opposite quadrant, lower left, it is flush tending towards countersunk. That is what made me think there could be some misalignment. The BB shell width is maximum 67.5mm

Nessism

Do you have a spare NDS cup you can try? Ideally an old school type with the shoulder on the outside. That will tell you if the shell is not faced perpendicular to the threads.

Taking the frame to a shop to have the BB threads and faces chased would be worthwhile too.

guy153

It looks like either the threads are misaligned or it hasn't been faced. A priori you would expect the faces to have more error than the alignment of the threads. If that's the case then it's all fine because that kind of BB is aligned to the threads not to the shell faces so it wouldn't matter if they hadn't been faced. So it's a dilly of a pickle. On the other hand if the cranks spin freely then it's probably fine.

unterhausen

If I had that problem I would find a shop that can face and chase the bb shell.

dsaul

I'd say that shell has not been faced. It was probably just masked by whatever plug they stick in there before painting. Facing will make the shell perpendicular to the threads. The ovalization is caused by the welding you can see just above that area and can't be changed. On a bike intended to take a cartridge style bottom bracket, I don't think I would worry too much about it. If the aesthetics of it bother you, have it faced.

unterhausen

That was not faced post-weld. I do frame prep for a local shop sometimes and we don't face bb shells if there isn't going to be anything in contact with it. So for a Shimano-style cartridge, we only face the drive side. What I see in that picture is pretty typical for an aluminum frame, although the ovalization seems extreme in this case.

timo888 

With the paint mist around the perimeter it does seem the BB shell wasn't faced at the factory. The drive side looks the same, paint-wise. But is it common for a nominal 68mm shell to be only 67.5mm wide, and even several fractions of a mm less than that in places, before facing?

Also, the frame shipped with a hollowtech BB52 BB (but not yet installed). I installed the cartridge BB only because the hollowtech crankset I'd ordered went into a USPS black hole and I happened to have a square taper crankset on the shelf.

unterhausen

People only rarely measure the width of bb shells, so it's hard to say if those dimensions common or not. I don't think it says anything about this particular frame.

The shells that framebuilders buy are usually a little wider than their nominal width, so that they can be faced after the frame is built. In any event, the width isn't critical in most cases, I'm sure there are exceptions that I'm not aware of.