Is there a tool to gauge whether DS and NDS thread are on the same axis?
#26
Senior Member
Thread Starter
...The joining process causes the shell to shrink in the areas where other tubes are joined(seat tube/down tube and chainstays), so chasing the threads and facing the shell is necessary to correct any distortion that occurred. Without facing, the shell will be wider in the area where no tubes where joined to it and the faces will not be parallel to each other. The faces being parallel is more important for modern external bottom brackets, as the thread tolerance will allow the cup to shift off axis to match the face of the shell. The threading would have to be terribly off axis to cause a noticeable problem and there is not a ton of excess shell thickness to allow the threads to get too far off axis.
P.S. The steerer insert you turned is working beautifully! :-)
__________________
novis rebus studentem
novis rebus studentem
#27
Senior Member
Join Date: Jan 2013
Location: South Jersey
Posts: 2,266
Mentioned: 18 Post(s)
Tagged: 0 Thread(s)
Quoted: 714 Post(s)
Liked 800 Times
in
475 Posts
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.
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.
Last edited by dsaul; 02-04-21 at 07:06 AM.
#28
Senior Member
Thread Starter
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 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.
__________________
novis rebus studentem
novis rebus studentem
Last edited by timo888; 02-04-21 at 08:58 AM.
#30
Senior Member
Thread Starter
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
__________________
novis rebus studentem
novis rebus studentem
Last edited by timo888; 02-04-21 at 09:07 AM.
#31
Banned.
Join Date: Jun 2004
Location: Torrance, CA
Posts: 3,061
Bikes: Homebuilt steel
Mentioned: 18 Post(s)
Tagged: 0 Thread(s)
Quoted: 2193 Post(s)
Liked 425 Times
in
337 Posts
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.
Taking the frame to a shop to have the BB threads and faces chased would be worthwhile too.
#32
Senior Member
Join Date: Dec 2019
Posts: 955
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 321 Post(s)
Liked 263 Times
in
212 Posts
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
#33
Randomhead
Join Date: Aug 2008
Location: Happy Valley, Pennsylvania
Posts: 24,396
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Liked 3,696 Times
in
2,517 Posts
If I had that problem I would find a shop that can face and chase the bb shell.
#34
Senior Member
Join Date: Jan 2013
Location: South Jersey
Posts: 2,266
Mentioned: 18 Post(s)
Tagged: 0 Thread(s)
Quoted: 714 Post(s)
Liked 800 Times
in
475 Posts
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.
Likes For dsaul:
#35
Randomhead
Join Date: Aug 2008
Location: Happy Valley, Pennsylvania
Posts: 24,396
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Liked 3,696 Times
in
2,517 Posts
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.
Likes For unterhausen:
#36
Senior Member
Thread Starter
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.
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.
__________________
novis rebus studentem
novis rebus studentem
#37
Randomhead
Join Date: Aug 2008
Location: Happy Valley, Pennsylvania
Posts: 24,396
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Liked 3,696 Times
in
2,517 Posts
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.
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.