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Variations in tolerance / thread pitch with English thread Campy bb cup ?

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Variations in tolerance / thread pitch with English thread Campy bb cup ?

Old 05-12-17, 11:49 PM
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Variations in tolerance / thread pitch with English thread Campy bb cup ?

Hi folks - have tried to fit a set of Campy thick bb cups to a frame twice now - one bike was a Centurion, one a 60s Paramount - in both cases, the fixed cup was a VERY tight fit, binding at points, while other (shimano, suntour, tange) cups threaded in smoothly, no issues. I even had the Centurion's threads chased - this made it possible to use the cup but it still was far from a silky thread-in. I'm not having the issue with the adjustable cup, though that too, is a tighter fit. I've cleaned up the threads very well - shouldn't be an issue, but still there is one. Anyone know if there were tighter tolerances or a slight variation in pitch / outside thread diameter with these cups? Is this typical? I'd rather use these for the Paramount I'm building, but really don't want to have to chase the threads on it - they're in good shape. And yes, I've double checked the size on both cups -
definitely English. Thanks for your input!

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Old 05-13-17, 07:17 AM
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As an engineer in manufacturing, I can tell you that there are variations in major diameters on cut external threads. If the threads are sharp, then there has been no 'truncation' of the peaks of the thread profile, and it will be difficult to thread in to a shell with a larger thread root radius. If you actually 'tap' the bottom bracket, it should go in easier, but often, 'chase' taps are not as aggressive as a good machining tap is.

If you have a lot of trouble getting your cup in, you could try VERY CAREFULLY sanding or grinding the peaks of the threads. You do not want to take off more than maybe .002" of the major diameter, though. I have noticed that Italians seem to go very sharp on thread profiles, whereas other countries do not, making an Italian cup difficult to put into a non-Italian shell.
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Old 05-13-17, 07:36 AM
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Campagnolo did make oversize thread cups, post an image of the exteriors
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Old 05-13-17, 08:50 AM
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Originally Posted by AlexCyclistRoch
As an engineer in manufacturing, I can tell you that there are variations in major diameters on cut external threads. If the threads are sharp, then there has been no 'truncation' of the peaks of the thread profile, and it will be difficult to thread in to a shell with a larger thread root radius. If you actually 'tap' the bottom bracket, it should go in easier, but often, 'chase' taps are not as aggressive as a good machining tap is.

If you have a lot of trouble getting your cup in, you could try VERY CAREFULLY sanding or grinding the peaks of the threads. You do not want to take off more than maybe .002" of the major diameter, though. I have noticed that Italians seem to go very sharp on thread profiles, whereas other countries do not, making an Italian cup difficult to put into a non-Italian shell.
Thanks - I think you may be right about the thread peaks, though they actually seem flatter on top than the other cups - I did try to sand them just a bit - didn't do much. Might have the BB chased, but if that's just enough to get the cups in - I just figure if it's binding a bit now, if I ever need to get the cups off again ... and I wouldn't want to risk a machinist's tap in the hands of anyone but a machinist. May end up going with the other cups I have. It doesn't need to be a show bike down to the last detail.
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Old 05-13-17, 08:53 AM
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Originally Posted by repechage
Campagnolo did make oversize thread cups, post an image of the exteriors
Can't get an image up right now - is there a marking you're looking for? Again, the adjustable cup gives me no problem, so I doubt it's actually an oversize cup unless at some point they were mismatched.
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Old 05-13-17, 09:23 AM
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BITD is was common knowledge that Campy Bb cups had "taller/sharper" threads then others did. We went to Campy cups a number of times when lower cost ones were sloppy/loose in the shell. Of course back then thin walled Campy cups were also available. Andy.


BTW Campy also had labeled oversize cups but that's not what I just referred to.

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Old 05-13-17, 09:35 AM
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I would seek out some reliable shop with experienced adult mechanics and Campy tools to align tap and face the bottom bracket in a proper fashion. This does not "injure" the BB in any way and is/was SOP with every quality frame I have ever had. Cheapo God know what non-aligned taps may not provide the same non-injury service. Your bike - your decision.
Besta luck
JMO of course

Charlie

Last edited by SteelCharlie; 05-13-17 at 09:39 AM.
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Old 05-13-17, 10:20 AM
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Originally Posted by SteelCharlie
I would seek out some reliable shop with experienced adult mechanics and Campy tools to align tap and face the bottom bracket in a proper fashion. This does not "injure" the BB in any way and is/was SOP with every quality frame I have ever had. Cheapo God know what non-aligned taps may not provide the same non-injury service. Your bike - your decision.
Besta luck
JMO of course

Charlie
I may do that, but I'll have to find a new shop. The guy I really trusted who had the aligned campy tool went out of business. Last time I had it done, it came out ok, but the guy used a non aligned hand tap that made me nervous ...
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Old 05-13-17, 10:26 AM
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Originally Posted by Andrew R Stewart
BITD is was common knowledge that Campy Bb cups had "taller/sharper" threads then others did. We went to Campy cups a number of times when lower cost ones were sloppy/loose in the shell. Of course back then thin walled Campy cups were also available. Andy.


BTW Campy also had labeled oversize cups but that's not what I just referred to.
Ok, so this is typical - good to know. Now it's just a decision whether to seek out a shop I trust or to use the cups that already fit.

Still funny the way the adjustable side goes in so smoothly and the fixed is binding ...
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Old 05-13-17, 02:44 PM
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Originally Posted by Andrew R Stewart
.....

BTW Campy also had labeled oversize cups but that's not what I just referred to.
I assume that was for people who had 'bad' threads, and cleaned them up by using an oversize tap? Very common practice in machining, for everything from making bolts go in easier, to allowing plating tolerance.

To the original poster: chase your threads, and apply some anti-seize compound to the threads. This will not only make it easier to remove the cup, but it will also act act a lubricant going in.
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Old 05-13-17, 03:02 PM
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Originally Posted by SteelCharlie
I would seek out some reliable shop with experienced adult mechanics and Campy tools to align tap and face the bottom bracket in a proper fashion. This does not "injure" the BB in any way and is/was SOP with every quality frame I have ever had. Cheapo God know what non-aligned taps may not provide the same non-injury service. Your bike - your decision.

Ditto. In every shop I worked at, we always chased the threads before installing a new campy BB, or frankly any BB when working on a high end bike. Generally the shell would get faced as well, even if it was a quick light scrape just to make sure everything is plumb.

Chasing does not harm the threads if done with a correct tool. If it's a new frame, it will clean up any paint or flux or drips or whatever. If it's old it will clean out dirt, dried grease, rust, whatever. Doing it freehand though?? Sounds like a bad idea. What bike shop doesn't have a BB thread chaser? Times have changed.
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Old 05-13-17, 08:27 PM
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Originally Posted by AlexCyclistRoch
I assume that was for people who had 'bad' threads, and cleaned them up by using an oversize tap? Very common practice in machining, for everything from making bolts go in easier, to allowing plating tolerance.

To the original poster: chase your threads, and apply some anti-seize compound to the threads. This will not only make it easier to remove the cup, but it will also act act a lubricant going in.

No, not that I know of. I've not heard of OS taps in the bike business (but do know of their use in industry otherwise). The bike business is one of loose tolerances and lots of out sourcing. BB cups were often poorly made, BB taps in factories old and not well maintained. If one thinks of low grade Asian stuff today being questionable then don't look at the base level Euro bikes of the 1970s... Remember so much of that era's manufacturing was done by low paid hands, not well engineered tooling in low paid hands.


Today we still have examples of the lax tolerances of the bike business. Witness PF30 with it's plastic fitting sleeves. Or Trek's needing to stock a special OS Bb bearing due to carbon shells not ending up dimensionally where they should be.


But back to campy OS cups- As I understand it they were to be used in BBs that were stretched or over cut. I never had to install any. I have gone to Campy std cups a number of times when others would jump a thread under tightening. I also have gone to PHIL BBs with LockTite in similar cases. Andy
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Old 05-13-17, 11:04 PM
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Originally Posted by AlexCyclistRoch
I assume that was for people who had 'bad' threads, and cleaned them up by using an oversize tap? Very common practice in machining, for everything from making bolts go in easier, to allowing plating tolerance.

To the original poster: chase your threads, and apply some anti-seize compound to the threads. This will not only make it easier to remove the cup, but it will also act act a lubricant going in.
Ok - I'm convinced - going to search out a shop with the right Campy tool and have it chased and faced. Then I'll use anti seize (have a lifetime supply of Permatex) instead of grease - only other time I've used that is on my Ti Serotta - seatpost, stem and BB. Never thought it was necessary or desirable on steel to steel or aluminum to steel. Guess there's no reason it shouldn't be!
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Old 05-13-17, 11:22 PM
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What folks need to keep in mind, is that under normal circumstances threads do not touch each other at the peaks and troughs. The profile standards are designed so troughs are cut deeper than peaks are high, so there will always be a gap there.

Threads engage on the flanks, as shown below so sanding down the tips is a meaningless exercise. (note the gaps).



The critical dimension where parts actually mate is called the pitch diameter. To understand this imagine taking a threaded tube, like a fork steerer, splitting it, then spreading it open slightly. Even if you then sand down the tips back to the original diameter, the thread is still larger.

Pitch diameter is measured a few ways. The easiest is by using a screw thread micrometer, having one anvil with a V-groove, and the other a point, so they directly measure the V flanks of a thread. The other common way is by winding a wire of known diameter, then measuring across the wire as shown here.



FWIW - there has long been a small difference in pitch diameter between Campagnolo and Shimano 1.370" threads, and we were aware of BITD when shops prepped frames with Campy taps, then found that Shimano cups had sloppy fits. Note that this difference in pitch diameter and fit tolerance existed even when the major diameter of the threads was identical.
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Old 05-14-17, 07:34 AM
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Originally Posted by FBinNY
What folks need to keep in mind, is that under normal circumstances threads do not touch each other at the peaks and troughs. The profile standards are designed so troughs are cut deeper than peaks are high, so there will always be a gap there.

Threads engage on the flanks, as shown below so sanding down the tips is a meaningless exercise. (note the gaps).



The critical dimension where parts actually mate is called the pitch diameter. To understand this imagine taking a threaded tube, like a fork steerer, splitting it, then spreading it open slightly. Even if you then sand down the tips back to the original diameter, the thread is still larger.

Pitch diameter is measured a few ways. The easiest is by using a screw thread micrometer, having one anvil with a V-groove, and the other a point, so they directly measure the V flanks of a thread. The other common way is by winding a wire of known diameter, then measuring across the wire as shown here.



FWIW - there has long been a small difference in pitch diameter between Campagnolo and Shimano 1.370" threads, and we were aware of BITD when shops prepped frames with Campy taps, then found that Shimano cups had sloppy fits. Note that this difference in pitch diameter and fit tolerance existed even when the major diameter of the threads was identical.
Always loved that Carlin quote.
Ok, I get most of what you're saying and you've corroborated that the Shimano and Campy threads are likely different in pitch diameter. But I still can't explain why the adjustable cup presents no problem and the fixed one does. If it were a thread issue, both would not fit. Is it possible that the peaks are touching not the troughs but buildup of hardened grit in those troughs which would naturally be heavier on the drive side? The threads look clean in the shell - I've degreased then and chased them with an awl, but perhaps I didn't reach deep enough. Perhaps I should try to get an Xacto knife in there. I could have it chased, but then I'd never be able to test my hypothesis... ...

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Old 05-14-17, 07:47 AM
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FWIW, I have seen both 1.370" and 1.375" pŘ used in bottom brackets. A difference of .005" will make a fit either very sloppy or very tight (to the point of nearly being impossible). Also, on most 'quality' turned parts, the major Ř is turned after the threads are cut. On less 'quality' parts, this is skipped, and the threads are raw and sharp. In more recent times, a lot of threads are rolled.
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Old 05-14-17, 07:49 AM
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Originally Posted by Andrew R Stewart
No, not that I know of. I've not heard of OS taps in the bike business (but do know of their use in industry otherwise). The bike business is one of loose tolerances and lots of out sourcing. BB cups were often poorly made, BB taps in factories old and not well maintained. If one thinks of low grade Asian stuff today being questionable then don't look at the base level Euro bikes of the 1970s... Remember so much of that era's manufacturing was done by low paid hands, not well engineered tooling in low paid hands.
Well, taps were poorly maintained, then the cut of BB shells would be UNDERsize, not oversize...And dies would make OVERsized cups......
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Old 05-14-17, 08:01 AM
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Originally Posted by msl109
is there a marking you're looking for? Again, the adjustable cup gives me no problem, so I doubt it's actually an oversize cup unless at some point they were mismatched.
They could be marked 1.390 x 24tpi in an overstrike:

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Old 05-14-17, 08:06 AM
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Back to the OP: Whenever I've had a frame's BB "chased and faced" by a really good technician using quality, well-maintained tools, I've been very happy with the result. The BB installation then went "like buttah!"
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Old 05-14-17, 08:46 AM
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So I cleaned out the threads some more with a straight pin and a stiff fine brush and microfiber cloth. Then I liberally applied anti seize. Though still not smooth like the adjustable cup, it went in with only occasional need of gentle wrench persuasion. The tolerances Campy specs obviously result in a VERY tight fit. Overkill imho, but I don't know much. In any case, the cup is all flush with the bracket face, which is my test of ok-ness. Just hope the lube I use for the bearings doesn't get contaminated with the anti seize surplus. I think that would be less than ideal.
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Old 05-14-17, 09:55 AM
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Originally Posted by AlexCyclistRoch
...... Also, on most 'quality' turned parts, the major Ř is turned after the threads are cut. On less 'quality' parts, this is skipped, and the threads are raw and sharp......
I'm sorry, but this is 100% pure bull.

It is very rare, make that extremely rare, to do any kind of pass after the threads are cut, in any manufacturing. The thread cutting or forming tools include the entire form; crest, flank, and root.

The blank is always turned to the major diameter prior to threading to minimize the work done by the threading tool. (or pitch diameter for formed threads). Making a pass after threading is both unnecessary, and risks pushing a burr out onto the flanks. It's just not done.

Since you work in a manufacturing environment, I suggest you head out to the shop floor and try to learn more about the processes involved.

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Old 05-14-17, 04:42 PM
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Originally Posted by FBinNY
I'm sorry, but this is 100% pure bull.

It is very rare, make that extremely rare, to do any kind of pass after the threads are cut, in any manufacturing. The thread cutting or forming tools include the entire form; crest, flank, and root.

The blank is always turned to the major diameter prior to threading to minimize the work done by the threading tool. (or pitch diameter for formed threads). Making a pass after threading is both unnecessary, and risks pushing a burr out onto the flanks. It's just not done.

Since you work in a manufacturing environment, I suggest you head out to the shop floor and try to learn more about the processes involved.
With aluminum, I've seen it done both ways (but never yet on steel), mostly on parts where the customer demands a close tolerance on the major Ř (military prints often demand this). My shop believes that a light final cut with a very sharp tool will almost always remove any burrs.

But, yeah, as a quality engineer, I'm more concerned on the result rather than the process. I am not a machinist. I usually leave the minutiae of the process followed to the Fanuc programmer, and he's pretty tight-lipped about what he does.
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Old 05-14-17, 05:14 PM
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-----

Don Millberger, founder of Bicycle Research Products, made a trip to visit the Schwinn Paramount facility in the early 1970's. They showed him a large bin of Campag BSC bottom bracket cups which would not fit in the Paramount frame shells after tapping with the Campag taps.

So when he made his set of bottom bracket taps he intentionally made them several thousanths oversize to accommodate. The down side of this arrangement is that when one taps a shell with his taps and mounts non-over spec cups they tend to rattle around in there.

-----
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Old 05-14-17, 06:30 PM
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I've seen low-end oversize BB cups in .5mm steps to fix damaged BB threads, in combination with an adjustable BB tap.
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Old 05-15-17, 02:03 PM
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Originally Posted by Reynolds
I've seen low-end oversize BB cups in .5mm steps to fix damaged BB threads, in combination with an adjustable BB tap.
+1

Back in the early seventies bought a used all-chrome Atala which was NR equipped, save for an OMG type (three doggs) fixed cup marked 36.5. Asked seller about it and he said that is way it came. When I parted it out gave the cup with the frame for the new owner.

Campag shows oversize taps in the "Special" catalogue (dark blue cover).

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