Good peak amplitudes but slow to build up?

[mbwatch]

I've been working on a 1948 Bulova caliber 10BC (15j) from a job lot box of random broken watches. It's 10.5''' so not a tiny movement, and the balance is about average size for a movement this diameter, with screw weights. After cleaning and installing a correct genuine Bulova white alloy mainspring it is running quite well. I had to calculate the lift angle with slow motion video and it comes out at a very high 58° (especially compared to other Bulovas). I am not too worried about that because the amplitudes I am seeing visually do match what the timegrapher is reading out. I am getting 275-280 in both horizontal positions, and about 225-230 in verticals at full wind minus 30min, then about 245H and 205V at 24 hours. I am happy enough with all of this. I'd like the vertical amplitude a little higher but can't do much more to pivots without a jacot lathe.

What I don't understand is why it takes such a long time to climb to its max amplitudes in any position, and a change of position causes a big initial loss. If it's running DD at 270 and I flip it over to DU, amplitude will fall way down to about 220 before climbing slowly back to 270 over like 20 minutes. Similarly a change from DU/DD to PD will drop to 170 before climbing slowly up to 225. Traces are flat when it is settled. Obviously it won't have so much time to sit still on wrist.

I have not worked on many small movements, not that 10.5''' is so small. And I think this is the oldest wrist watch movement I have done. Is it normal to take so long to build amplitude on smaller balances? I checked balance end shake, but that seems to be correct. Train motion is excellent, new mainspring with lots of recoil sans pallet fork. It's in beat, 0.1ms DD and about 0.3ms DU. The pallet stones are lubricated with 9415, maybe too much? Balance has good free motion, easily surpassing 100 oscillations from a 180 starting point.

What else can I check if this is not expected behavior?

Edited March 13 by mbwatch
sp

[Klassiker]

My first thought was too much lubrication. Too much 9415 on the pallet stones? Maybe.

I suggest you test your theory by cleaning it off and running the tests with nothing on the stones.

[Nucejoe]

I suspect the  hairspring  " too weak " . 

Then did you visually check end stones?  

 

Rgds

 

Edited March 14 by Nucejoe
Correction

[JohnR725]

5 hours ago, mbwatch said:

20 minutes

20 minutes is outside of the range of the normal settling time of changing positions.

I might I had some theories but 20 minutes is a really long time. I did have to find a picture which I found at the link below typically with big heavy balance wheels there is a time for them to react to things.

What happens if you put the watch In a crown down position and just leave it on the timing machine do you see slow fluctuations? Then what happens if you leave it on the timing machine hours and check it every about 10 minutes five minutes how consistent is it after the initial 20 minute time?

 

https://ranfft.org/caliber/1386-Bulova-10BC

[mbwatch]

6 hours ago, Nucejoe said:

I suspect the  hairspring  " too long " . 

Then did you visually check end stones?  

 

I did check the end stones - not cracked and very clean. I redid the lubrication to ensure identical amounts of 9010.

4 hours ago, JohnR725 said:

What happens if you put the watch In a crown down position and just leave it on the timing machine do you see slow fluctuations? Then what happens if you leave it on the timing machine hours and check it every about 10 minutes five minutes how consistent is it after the initial 20 minute time?

I don't see any fluctuations - it stays flat. The amplitudes may rise and fall within about 10° as it sits but the rates don't change. Earlier rates did change, but I found & cleaned a spec of rust in the 3rd wheel pinion and that was solved. I can't watch it today but I'll monitor it tomorrow. I flipped it to crown down about a half hour ago and it is still climbing back up. It fell from 260 DU to 155 which is obviously too much.

Edited March 13 by mbwatch
sp

[nickelsilver]

How much endshake does the balance have? I have a feeling it's too much.

[Nucejoe]

 Heavy balance wheel or weak hairspring.

 Bet someone just fitted a weak spring to list the watch as runner and let you fix it. 

Rgds

 

 

 

 

 

[mbwatch]

3 minutes ago, Nucejoe said:

Bet someone just fitted a weak spring to list the watch as runner and let you fix it. 

No, this was just banging around the bottom of a box with 25 other watches and I decided to have a go at it.  It was very much a non-runner but I have it almost all the way back to life. The balance wheel and hairspring are matched because the rates are fine. If either of them were wrong, I wouldn't be able to get decent rates right?

[Nucejoe]

1 minute ago, mbwatch said:

 The balance wheel and hairspring are matched because the rates are fine. If either of them were wrong, I wouldn't be able to get decent rates right?

 Decent rate doesn't neccessarily mean the right spring and balance wheel match.

  You can practically get exact beat/rate out of any spring and balance wheel. Other parameters such as  acceptable  dynamic stability come to the picture  with a watch wrist specially, and if real bad match, heavy  balance wheel will take many impulse to reach max amp on bench, as its an inertial body.

But then what do I know? 

Richard Harris  knows I know nothing, but keeps it secret. 

 

[mbwatch]

3 minutes ago, Nucejoe said:

  You can practically get exact beat/rate out of any spring and balance wheel. Other parameters such as  acceptable  dynamic stability come to the picture  with a watch wrist specially, and if real bad match, heavy  balance wheel will take many impulse to reach max amp on bench, as its an inertial body.

Thank you for this explanation!

[VWatchie]

8 hours ago, mbwatch said:

I did check the end stones - not cracked and very clean.

I don’t necessarily think the following is the cause of the problem, but it came to mind when I read what you wrote.

It took me a long time to figure out how difficult it can be to detect pits in cap jewels—something I overlook far too often. If the pits are shallow, they can be very hard to spot. Nowadays, I always examine cap jewels under my stereo microscope at 40x magnification, angling them so that light reflects off the flat surface in the same way one creates a sunbeam reflection.

 

[nevenbekriev]

OK, 20 min. is much beyond normal. I don't suppose the balance is so heavy, simply no way. It must be some kind of energy loss which is provoked by position change and slowly disappears when in rest. Such thing may be guard pin touching the safety roller due lack of draw in the escapement. Is the draw present and reliable on both sides? Another thought - the drop lock can be minimal /unreliable. I expect to it be some kind of escapement problem.

In case it is not the escapement, can You do something like the free oscillations test, but to change the movement position while balance running and see if sudden drop of amplitude happens? It is normal to have some amplitude drop as there is gyroscopic effect that leads to forces that increase friction in balance bearings, but do it with another similar normal movement to have some idea what is expected and normal.

Did You check if the balance axial free play is normal as @nickelsilver suggested?

[nickelsilver]

1 hour ago, VWatchie said:

I don’t necessarily think the following is the cause of the problem, but it came to mind when I read what you wrote.

It took me a long time to figure out how difficult it can be to detect pits in cap jewels—something I overlook far too often. If the pits are shallow, they can be very hard to spot. Nowadays, I always examine cap jewels under my stereo microscope at 40x magnification, angling them so that light reflects off the flat surface in the same way one creates a sunbeam reflection.

 

It's true that the pit can be hard to see, got to have just the right angle of view with the right lightling. I just did a cool old Zenith auto for a friend, so trying to keep the cost down on a watch they might wear a few times a year (he has lots). The upper cap jewel showed a bit of a pit. Got it all together, and sure enough there was a good 15-20 degree difference in the horizontal positions, but the rates were great with a delta of 12s in 6 positions, and the lower of the horizontals was over 270, so I left it like that. Dude was happy and I was too.

 

I also don't think a pitted jewel is causing the issue here. I mention endshake as I have encountered some really weird issues that ultimately tracked down to excessive endshake on the balance. And in some cases the endshake was pretty OK compared to a lot of other pieces- but it was too much in these cases.

[mbwatch]

8 hours ago, nickelsilver said:

How much endshake does the balance have? I have a feeling it's too much.

 

1 hour ago, nevenbekriev said:

Did You check if the balance axial free play is normal as @nickelsilver suggested?

I just got home to look at it. I had left it crown down on the machine and came home to 190° at about 22 hours running. So not great but could be worse. The end shake maybe does feel like too much. I don't have any perceptible side shake but the amount of end shake feels about like what I would want on a pocket watch, and that's probably too much for a smallish wristwatch.

I am not sure I know how to adjust balance end shake on this kind of arrangement. Push the lower hole jewel in a hundredth? Can I adjust the end stone?

At the moment I have the dial & hands attached so I could test for worsening performance. I'll take those off later too, and verify I haven't done something stupid like fail to screw the end stone's plate down tightly.

 

(The lower is from a disassembly photo - it's not dirty like this)

Thank you for the escapement suggestions @nevenbekriev. I have low proficiency adjusting escapements but am willing to try on this watch since I paid really nothing for it and have a donor movement too.

[Nucejoe]

6 hours ago, mbwatch said:

I am not sure I know how to adjust balance end shake on this kind of arrangement.

Shimming  will do as a test for the end shake suspect idea.  

Insert a piece of thin aluminum foil between mainplate and cock on the outer premiter of mainplate. Tighten cock screw، this will tilt the cock so lowers its setting. 

 Depending on how deep you insert the aluminum foil in between cock and mainplate, you can fine adjust balance end shake.  A good end shake is one that if you tighten the  cock screw a bit, balance will get free to  oscilate.

End shake isn't easy to measure, but this method of balance just getting free is easy and solid.

Ps, end stone shown in last pic (the one on AS movement)  looks unusual as if it's been glued to its neighbor or whatever the previous guy could find to glue it to.

Good luck 

 

 

 

 

Edited March 14 by Nucejoe
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[mbwatch]

19 hours ago, Nucejoe said:

end stone shown in last pic (the one on AS movement)  looks unusual as if it's been glued to its neighbor or whatever the previous guy could find to glue it to.

I think this is a trick of light plus the photo was from before cleaning the movement. It looks normal in situ after cleaning.

 

Shimming to reduce end shake did help a lot. Instead of taking 20min to recover amplitude, now it takes only about 5min between DU/DD to recover 260-270° and less than 10min to rise to >200° when flipping to crown down (and it will still gain more if left alone). This sounds awful still but it is a major improvement over what was happening before. I'm going to case it and see how it works on wrist. "Good enough" will be good enough for this watch since I pulled it out of the bottom of a job lot box and the dial is pretty scarred up.

I do not mind leaving the foil shim in place for now, but still I need to learn how to adjust end shake properly for this balance. I have shimmed big pocket watch balance cocks before, and encountered lots of times when watchmakers had raised gouges in the metal under the balance cock to adjust shake but I don't want to hack up this mainplate.

[Nucejoe]

Is one screw of the two that hold end stone plate in place missing ?   

 

 

[mbwatch]

1 hour ago, Nucejoe said:

Is one screw of the two that hold end stone plate in place missing ?   

No, nothing missing. One screw on the dial side end stone plate, two screws under the balance cock all accounted for. That picture has light shining straight down into the jewel. This one lifted from Ranfft is what it actually looks like.

[Nucejoe]

Was reffering to the screw on( end stone plate)  balance cock, 

 

[rehajm]

wow. m..the reflection does make it appear the right screw is missing

[mbwatch]

5 hours ago, Nucejoe said:

Was reffering to the screw on( end stone plate)  balance cock, 

 

3 hours ago, rehajm said:

wow. m..the reflection does make it appear the right screw is missing

It does look missing in that photo. I promise all of you, both screws are there! They have polished tips and that black hole is probably the reflection of my phone when I took the picture.

[Nucejoe]

 In case you still have this watch on bench.

Curious to see a clear top view of balance complete with hairspring attached.

Funny as it may sound,  sometimes I can tell if hairspring quality can belong to balance wheel.  even funnier is I can't actually identify some metals . Fake and genuine gold jewelry or brass and copper for instance, not  in photos anyway.

 Not sure but quality of parts in  bulova seems superior to standard in my view, so expect to see finely finished balance complete.

Rgds

Edited March 15 by Nucejoe
Spell

[mbwatch]

19 minutes ago, Nucejoe said:

 In case you still have this watch on bench.

Curious to see a clear top view of balance complete with hairspring attached.

I have it assembled and cased so I can't show the balance complete alone. Best I have is this photo in situ but I expect that isn't good for you to see anything helpful. Thanks for your interest and continued suggestions anyway.

[nickelsilver]

So many factors come in to play, it does become a bit dizziyng. Just had an Omega 30mm caliber (26X something). One of the best movements of all time. Serviced, ran a ticket, 32 amplitude difference in horizontals, verticals dropped from 280 (max horizontal- other side was 248) to around 210. I retouched the balance staff ends, and moved the exit jewel in 0.02mm. I write this because a lot of times you can have the best cleaning solutions and methods, but, some watchmakingishness comes into play. I know folks here know that real watchmakers exist, but go on Reddit and try to explain something " real " and you are a gatekeeper. You do have to move pallet stones, bankings, tweek hairsprings. I do it on every job. Like, 30% of the time I retouch the escapement in some way, and 75% of the time I touch up the hairspring.

 

Here's the tickets from the Omega. It was like 20 minutes from one to the other.

 

It'a funny to see the actual average rate didn't change. But the overall performance is a LOT better. I also didin't touch the regulator once in the whole job.

Edited March 15 by nickelsilver

[mbwatch]

2 hours ago, nickelsilver said:

I write this because a lot of times you can have the best cleaning solutions and methods, but, some watchmakingishness comes into play. I know folks here know that real watchmakers exist, but go on Reddit and try to explain something " real " and you are a gatekeeper. You do have to move pallet stones, bankings, tweek hairsprings. I do it on every job. Like, 30% of the time I retouch the escapement in some way, and 75% of the time I touch up the hairspring.

Shimming this one for end shake helped tremendously though it's still not great in verticals and I suspect the pivots need burnishing. That's still outside my tooling and skillset so I'm going to leave it alone. Can these end stones be pushed in 0.01 to lessen the shake?

I am pretty sure I have spotted you on reddit under a different name, and honestly I cannot believe your restraint over there. There's a horrible dearth of experience on reddit, and very few people who hang around experienced or not, who are good communicators. This is why I try to squeeze so much out of all of you over here (thank you).