How much weaker mainspring should I get to stop re-banking?

[mikepilk]

I finally got round to restoring an ET/NFT (Eberle) 38 in a Waltham wrist watch which I've had for years.

I had to fit a new balance staff, and the hairspring took some re-shaping - the terminal curve was all wrong (suggesting it might be the wrong hairspring).

I fitted a new mainspring 1.8 x 0.10 x 280 (as listed by Ranfft and BestFit).

I thought I might be chasing amplitude, but it turns out I have too much. It runs fine until it starts re-banking. I've oiled the pallet pivot jewels, but that didn't help.

I can only think that the balance/hairspring may be wrong?

Does anyone know roughly how much a drop of 0.01 in strength will change the amplitude ? 

 

[JohnR725]

3 hours ago, mikepilk said:

I can only think that the balance/hairspring may be wrong?

I'm curious about your thinking here as to why you think this may be the problem?

3 hours ago, mikepilk said:

balance staff

When you fit the new balance staff did you polish the pivots?

3 hours ago, mikepilk said:

It runs fine until it starts re-banking. I've oiled the pallet pivot jewels, but that didn't help.

I've also seen recommendations of using HP 1300 on the balance pivots. I suppose you could try heavier oil on the pallet fork pivots but they can be better to figure out what the problem is.

 

[mikepilk]

3 minutes ago, JohnR725 said:

I'm curious about your thinking here as to why you think this may be the problem?

The terminal curve was the wrong shape - there barely was one.

4 minutes ago, JohnR725 said:

When you fit the new balance staff did you polish the pivots?

No

4 minutes ago, JohnR725 said:

I've also seen recommendations of using HP 1300 on the balance pivots. I suppose you could try heavier oil on the pallet fork pivots but they can be better to figure out what the problem is.

I tried HP1300 on both pallet pivots - didn't have a big effect.

I cannot find the lift angle for this movement. From what I can determine it's about 43°. Even with this setting it's reaching well over 300° before (what I think is) re-banking occurs. It's obvious on a pocket watch as you can clearly hear the "galloping". But it's not so easy to hear on a smallish movement.

The hairspring was covered in some goo, not sure what - so I did think it was coils sticking. I put it through the cleaning process twice, but it still didn't look spotless. Today I gave it a clean in the ultrasonic in acetone, then naphtha, then IPA. It looks a lot better now.  I'll see how it goes tomorrow.

I'm struggling to get good slow motion of the balance, to determine the lift angle, and see if any coils are sticking. My phone (Samsung A50) won't allow me to zoom when recording slo-mo. I can record through the microscope camera, then play back using VLC Video Player. But even at the slowest speed x0.25, it's hard to see what's going on.  Anyone got a better method?

[mikepilk]

I got the hairspring super clean and all coils nicely spaced.

I put a mark on the balance with tippex tape and determined lift angle is about 43°.

It started running nicely, steady plot, finally got beat error close to 0ms, amplitude  280°, 290° , 300­° - then re-banking  ahhhhhhh 

It's definitely re-banking as I can hear the galloping.

I measured the mainspring - it's the correct size.

I can't understand it - I'm going to give up on this one and put it back on the shelf 

 

Edited October 7, 2023 by mikepilk

[Neverenoughwatches]

26 minutes ago, mikepilk said:

I got the hairspring super clean and all coils nicely spaced.

I put a mark on the balance with tippex tape and determined lift angle is about 43°.

It started running nicely, steady plot, finally got beat error close to 0ms, amplitude  280°, 290° , 300­° - then re-banking  ahhhhhhh 

It's definitely re-banking as I can hear the galloping.

I measured the mainspring - it's the correct size.

I can't understand it - I'm going to give up on this one and put it back on the shelf 

 

With this potentially being a 70 odd year old movement, was the spring you removed of an equivalent material to today's bought ones. So could same size but a higher tensile strength be the cause ?

[JohnR725]

30 minutes ago, Neverenoughwatches said:

was the spring you removed of an equivalent material to today's bought ones. So could same size but a higher tensile strength be the cause ?

The modern white mainsprings as they're called are supposed to be stronger for the same thickness as an original blued steel spring.

On 10/5/2023 at 7:15 AM, mikepilk said:

new balance staff,

What would be interesting is if we had proper timing machine diagnostics. Like does this occur in dial down only what does the watch do in dial up and what happens if it's crown down? How do things look of its only wound 50% so it's not giving you a problem so we can see if there is a problem with maybe the pivots better perhaps?

It's assumed that the new balance staff is perfect. Unfortunately my experiences been that sometimes are not perfect there's the possibility at one end may be different than the other end or maybe they're just not shaped right at all. For instance images of how the pivot is supposed to be shaped it's actually supposed to be a little flat on the end because if it's not you end up with exactly the problem you're having. I did this in school when I was shaping the end of the pivot I made it nice and round and the timing machine made a really nice galloping sound.

1 hour ago, mikepilk said:

I measured the mainspring - it's the correct size.

Did you give up on the idea of going to weaker mainspring to see what would happen?

[Nucejoe]

On 10/5/2023 at 5:45 PM, mikepilk said:

I  can only think that the balance/hairspring may be wrong?

 If this was to be the case,  then hairspring must be noticably longer than original to produce the right frequency. 

 

Edited October 7, 2023 by Nucejoe

[Neverenoughwatches]

33 minutes ago, Nucejoe said:

 If this was to be the case,  then hairspring must be noticably longer than original to produce the right frequency. 

 

Help me to understand your thinking here Joe.  Are you saying a longer ( effectively weaker ) hs would add to the degree of rotation of the balance. I can understand as it has less strength to pull it back, but is also going to slow down the timing. 

[mikepilk]

It re-banks DU and DD. Vertical is OK as the amplitude drops enough. At less than full wind, the performance is good.

It's had an interesting history, as both balance hole jewels were just plain flat jewels 

Edited October 7, 2023 by mikepilk

[JohnR725]

Did we ever get a picture of the movement so we can see what were talking about?

On 10/5/2023 at 7:15 AM, mikepilk said:

I fitted a new mainspring 1.8 x 0.10 x 280 (as listed by Ranfft and BestFit).

Thinking about factory specified mainsprings. When the Elgin watch company was in business they used to have factory tours and of course in some supervisor's office there would be a book. The book that specifies everything which unfortunately has no pictures which is very sad still a book explaining what's to be shown all the details etc. I snipped out an image of the book for you something that was wondered about and maybe your watch has the same problem? We can see and I highlighted as one of the watches too much amplitude what do they do well it goes someplace where they swap it for a weaker barrel. They don't specify here but for some of their watches and the older material book they actually have weaker mainsprings. Here they just swap for a weaker barrel. I wonder if they leave a little note to stick a Post-it note the watch that they did this? What would happen in the future if you were servicing the watch a use the Factory specified mainspring?

Oh and what about something that were here we can blame it's a vintage watch using a blued steel spring there could be a lot of variation but what about newer watches like Rolex what about a 3135 it's a very common Rolex. How many mainsprings does it have an notice how one of them is what

[Nucejoe]

3 hours ago, Neverenoughwatches said:

 Are you saying a longer ( effectively weaker ) hs would add to the degree of rotation of the balance. 

Correct,   Longer HS  adds to the degree of rotation, be it of the same CGS No or weaker.

What I am saying is;   in adition to the terminal curve suggesting wrong hairspring, the length of hairspring thus radius of the coil could suggest wrong hairspring. 

Providing long enough, any hairspring on a balance wheel can produce the desired frequency, one limiting factor in matching balance-hairspring is diameter of the coil. 

Smart of Mike to interpret his observance of the unshapely terminal curve/ coil  as possible wrong hairspring.

I would try the old or a weaker new mainspring.

Rgds

 

 

 

 

 

 

[mikepilk]

That's an interesting read @JohnR725

The question is John and @Nucejoe, is the weaker spring .01 or .02 weaker in thickness?

 

1 hour ago, JohnR725 said:

Did we ever get a picture of the movement so we can see what were talking about?

 

Edited October 7, 2023 by mikepilk

[Neverenoughwatches]

7 hours ago, JohnR725 said:

When the Elgin watch company was in business they used to have factory tours and of course in some supervisor's office there would be a book. The book that specifies everything which unfortunately has no pictures which is very sad still a book explaining what's to be shown all the details etc. I snipped out an image of the book

I'm trying to understand if the book that specifies everything in some supervisor's office somehow went walkies during a factory tour that was attended by a guy called John . Considering that said John is now able to snip images from said book .

[JohnR725]

8 minutes ago, Neverenoughwatches said:

I'm trying to understand if the book that specifies everything in some supervisor's office somehow went walkies during a factory tour that was attended by a guy called John . Considering that said John is now able to snip images from said book

I would've loved to visit the factory but never did. I obtain the book from somebody who used to visit Elgin Illinois and purchase things from former factory workers. As expected from a factory internal document no copyright date but based on the history part of the factory it probably came into existence about 1955.

 

 

[Neverenoughwatches]

3 minutes ago, JohnR725 said:

I would've loved to visit the factory but never did. I obtain the book from somebody who used to visit Elgin Illinois and purchase things from former factory workers. As expected from a factory internal document no copyright date but based on the history part of the factory it probably came into existence about 1955.

 

 

Praise to former watch factory workers with incentive to aquire things with interesting information that might have otherwise been lost forever. 

[mikepilk]

18 hours ago, mikepilk said:

is the weaker spring .01 or .02 weaker in thickness?

Answering my own question :

I've just completed service/repair on a Movado 150MN which was re-banking.
(Odd that the two watches I'm currently working on have the same problem!).

The mainspring measured 1.30 x 0.11, which is incorrect. When fitted with the correct 1.30 x 0.10, the amplitude is about 270°.

So a reduction in thickness of 0.01 was enough to fix it.

[ I remember reading that wound springs can be considered as rectangular beams in bending, with moment of Inertia bd³/12
i.e. it depends on thickness cubed. So (0.10/0.11)³ = 0.75. So a reduction in strength of 25% - quite a lot ]