What causes DU/DD anisochronism?

[swordfish]

I'm not even sure that this is the right terminology. I notice that when my old Bulova is dial up it gains ~73 seconds/ day (See first image), but when I flip the Tiimegrapher to dial down, it loses ~45 seconds/day. (The second image shows the new pattern on the left with the remnant of the old pattern on the right.). (I also note that the beat error differs.)

My question is mainly a theoretical one. I think I understand how an untrued hairspring or balance wheel, or an unpoised balance wheel could cause a difference between dial up and pendant up time keeping. But in DD vs DU, the plane of that error hasn't changed. I don't understand how those defects could cause a DD vs DU discrepancy.

So if those problems do in fact cause this type of anisochronism, how does that happen? If that is not the defect, what could be?

[matabog]

just thinking out loud:

maybe the regulator pins are not paralel and when You turn the watch, because of the end shake of balance, the hair spring will modify its position in-between the regulator pins.

these things have more effect when You have low amplitude

[matabog]

http://raulhorology.com/2012/12/the-mark-of-a-true-watchmaker-forming-hairsprings-part-4-pinning-to-the-stud-final-adjustments/

 

about hs position în the regulator

[clockboy]

On 28 August 2016 at 9:47 PM, swordfish said:

I'm not even sure that this is the right terminology. I notice that when my old Bulova is dial up it gains ~73 seconds/ day (See first image), but when I flip the Tiimegrapher to dial down, it loses ~45 seconds/day. (The second image shows the new pattern on the left with the remnant of the old pattern on the right.). (I also note that the beat error differs.)

My question is mainly a theoretical one. I think I understand how an untrued hairspring or balance wheel, or an unpoised balance wheel could cause a difference between dial up and pendant up time keeping. But in DD vs DU, the plane of that error hasn't changed. I don't understand how those defects could cause a DD vs DU discrepancy.

So if those problems do in fact cause this type of anisochronism, how does that happen? If that is not the defect, what could be?

It could be too much end shake or jewel issue. The link shown by Matabog is well worth looking at. 

[szbalogh]

I also bet on jewel and/or endshake problem if the hairspring is ok.

[oldhippy]

End shake is the most likely cause.Ware is another. It could even be down to the amount of oil and if you used the correct one.

[JohnR725]

It's a shame you don't have a different timing machine as this one does not measure amplitude. What we cannot tell is if you're having a dramatic change in amplitude because the amount of friction on one side versus the other. Dramatic amplitude change can have a dramatic timing change.

[swordfish]

Oldhippy indirectly gets to the heart of my theoretical puzzlement. Whether a watch is dial-up or dial-down, its wheels have the same amount of end shake, no? So how does excessive end shake cause anisochronism?

I can imagine, however, that a faulty pinion, jewel, or oil could cause DD vs DU anisochronism, since (I suspect) there is more frictional resistance on the inferior pivot/jewel interface than on the superior one.

My concern about this is for basic understanding of watch mechanics, not concerning any particular watch now under my dubious care.

JohnR725, I've been contemplating upgrading my Timegrapher as you recommend. I'll probably do that soon. But does the periodicity of a hairspring depend on its arc of swing (amplitude)? I can see how the amplitude of a pendulum would be important, since its rate does in fact vary slightly with extremes of swing. But is that also true for hairsprings? I thought—perhaps incorrectly—that the rate of a hairspring depended only on its length and intrinsic metallic properties and the mass [impedance] of the balance wheel, and not on its amplitude.

Sent from my iPad using Tapatalk

[matabog]

please read the article I posted above. Raul explains how the amplitude affects timing and how centering the hs in-between the regulator pins is so vital.

[JohnR725]

Everything in the watch affects timekeeping..  Gross oversimplification  but everything does.. I should probably read the article first but  the number one thing that affects  timekeeping is the escapement. The escapement supplies energy to the balance wheel  but  it also interferes  with the timekeeping.. It's why the escapement has to be adjusted properly which is overlooked by  most hobbyists.. Like if the depth the locking is too deep  all that time spent unlocking his loss of energy but it slows the balance wheel swing down..  So escapement is a necessary evil  supplying energy  to the Balance wheel. If you look at the typical lift angle of 52°  This corresponds to the time  that the balance wheel  is engaging  with the escapement..

So if you have a bad pivot bad are timing dial-up and dial down and see a dramatic drop in amplitude  you will see a change in timekeeping..  If you're lucky you can just  clean up the pivots they both have to be the same and strangely enough the end of the pivots  have to be flat or slightly domed  not dramatically rounded because they actually have to have friction.  You're trying to get the ends of the pivots  to have as much contact area the same as  the sides  so the friction is the same everywhere the amplitude is the same in all positions  then the effect of the escapement  will be the same  otherwise you get goofy timekeeping.  Then if you get dramatically enthusiastic  rounding the pivots the roller jewel will crash into the other side of the fork  making a really interesting sound that's very bad.